Scientific American Supplement, No. 595, May 28, 1887
by
Various
Part 1 out of 3
Produced by by Don Kretz, Juliet Sutherland, Charles Franks and the
DP Team
[Illustration]
SCIENTIFIC AMERICAN SUPPLEMENT NO. 595
NEW YORK, MAY 28, 1887.
Scientific American Supplement. Vol. XXIII, No. 595.
Scientific American established 1845
Scientific American Supplement, $5 a year.
Scientific American and Supplement, $7 a year.
* * * * *
TABLE OF CONTENTS.
I. BOTANY.--The Relation of Tabasheer to Mineral Substances.--The
composition of this curious secretion of the bamboo.--Analyses
and properties of the material, according to various
observers.--Its appearance under the microscope. 1 illustration.
II. CHEMISTRY.--Apparatus for Drying Flour.--An apparatus for
determining the moisture in flour. 1 illustration.
III. ELECTRICITY.--Automatic Commutator for Incandescent
Lamps.--An apparatus for lighting automatically a new lamp to
replace one that has failed. 1 illustration.
Definitions and Designations in Electro-Technics.--Mr. Jamieson's
proposed code of electric symbols--literal and graphic. 4
illustrations.
IV. ENGINEERING.--New Dredging Machinery.--The dredger Ajax,
recently built in California.--Its dimensions and capacity. 1
illustration.
Reservoir Dams.--By DAVID GRAVELL.--The engineering details
of dams.--Typical masonry and earthwork dams of the world. 23
illustrations.
The Flexible Girder Tramway.--A new type of suspended railway--a
modification of the wire tramway system. 21 illustrations.
V. HYGIENE.--Climate in its Relation to Health.--By G.V. POORE,
M.D.--The third lecture of this series.--Consideration of the
floating matter of the air and diseases caused thereby.--Causation
of hay fever.
VI. MATHEMATICS.--Radii of Curvature Geometrically Determined.--By
Prof. C.W. MACCORD, Sc.D.--No. VII. Path of a
point on a connecting rod. 3 illustrations.
VII. MICROSCOPY.--Improved Microscopical Settling Tube.--By F.
VANDERPOEL.--New tubes for use in urinary analysis. 4
illustrations.
VIII. MISCELLANEOUS.--Apparatus for Manufacturing Bouquets.--An
ingenious machine for facilitating the construction of
bouquets. 1 illustration.
Bozerian's Refrigerant Punkas.--A fan worked by the feet, a
substitute for the Indian punka. 2 illustrations.
How to Make a Kite without a Tail.--An improved form of kite
described and illustrated. 1 illustration.
Punkas.--By J. WALLACE, C.E.--The mechanics of punkas;
experiments on their rate of swing.
The Edible Earth of Java.--An account of this curious substance,
its taste and appearance.
IX. NAVAL ENGINEERING.--Another Remarkable Torpedo Boat.--Over
twenty-eight miles an hour.--Full particulars of the trial of
one of the new Italian torpedo boats, built by Yarrow & Co.
Copeman & Pinhey's Life Rafts.--A new life raft for use on
steamers, folding into deck settees. 3 illustrations.
X. PHYSICS.--Sunlight Colors--By Capt. W. DE W. ABNEY.--A valuable
lecture on the cause of the colors of the sun, and their relative
intensities. 3 illustrations.
The Wave Theory of Sound Considered.--By HENRY A. MOTT,
Ph.D., LL.D.--Arguments against the generally accepted theory
of sound.
* * * * *
COPEMAN & PINHEY'S LIFE RAFTS.
The experiments with life saving appliances which Mr. Copeman brought
before the delegates of the Colonial Conference, on the 13th April, at
the Westminster Aquarium, had a particular interest, due to the late and
lamentable accident which befell the Newhaven-Dieppe passenger steamer
Victoria. In many cases of this nature, loss of life must rather be
attributed to panic than to a want of life saving appliances; but, as a
general rule, an abundant supply of such apparatus will tend to give
passengers confidence, and prevent the outbreak of such discreditable
scenes on the part of passengers as took place on the Victoria.
[Illustration: FIG. 1.--COPEMAN & PINHEY'S LIFE RAFTS.]
Messrs. Copeman & Pinhey have, for some years past, done good work in
this direction, and at the recent meeting of the Institution of Naval
Architects, Mr. Copeman showed several models of the latest types of
their life saving apparatus, both for use on torpedo boats and passenger
steamers. Our illustration (Fig. 1) represents the kind of rafts supplied
to her Majesty's troop ships, while Figs. 2 and 3 show deck seats
convertible into rafts, which are intended for ordinary passenger
steamers. The raft shown in Fig. 1 consists of two pontoons, joined by
strong cross beams, and fitted with mast, sail, and oars. When not in
use, the pontoons form deck seats, covered by a wooden grating, which in
our illustration forms the middle part of the raft. Each pontoon has a
compartment for storing provisions, and when rigged as a raft, there is a
railing to prevent persons being washed overboard.
[Illustration: FIG. 2.]
[Illustration: FIG. 3.]
The seat life buoy, shown in Fig. 2, serves as an ordinary deck seat,
being about 8 ft. long, and it consists of two portions, hinged at the
back. When required for use as a life buoy, it is simply thrown forward,
the seat being at the same time lifted upward, so that the top rail of
the back engages with the two clips, shown at either end of the seat, and
the whole structure then forms a rigid raft, as will be seen from Fig. 3.
Several other appliances were shown at the Westminster Aquarium on April
13, but the two rafts we have selected for illustration will give a
sufficiently correct idea of the general principles upon which the
apparatus is based.--_Industries._
* * * * *
ANOTHER REMARKABLE TORPEDO BOAT--OVER TWENTY-EIGHT MILES AN HOUR.
In a recent impression we gave some particulars of the trial trip of a
boat built for the Italian government by Messrs. Yarrow & Co., which
attained the highest speed known, namely, as nearly as possible, 28 miles
an hour. On the 14th April the sister boat made her trial trip in the
Lower Hope, beating all previous performances, and attaining a mean speed
of 25.101 knots, or over 28 miles an hour. The quickest run made with the
tide was at the rate of 27.272 knots, or 31.44 miles per hour, past the
shore. This is a wonderful performance.
In the following table we give the precise results:
+-------+---------+-------+-----+-------+-------+-------+
| | | | | | | Second|
|Boiler.|Receiver.|Vacuum.|Revs.| Speed.| Means.| Means.|
+-------+---------+-------+-----+-------+-------+-------+
| | | | per | Knots | Knots | Knots |
| lb. | lb. | in. | min.|per hr.|per hr.|per hr.|
+-------+---------+-------+-----+-------+-------+-------+
1 | 130 | 32 | 28 |373 | 22.641| 24.956| |
2 | 130 | 32 | 28 |372.7| 27.272| 25.028| 24.992|
3 | 130 | 32 | 28 |372 | 22.784| 25.028| 25.028|
4 | 130 | 32 | 28 |377 | 27.272| 25.248| 25.138|
5 | 130 | 32 | 28 |375 | 23.225| 25.248| 25.248|
6 | 130 | 32 | 28 |377 | 27.272| | |
------+-------+---------+-------+-----+-------+-------+-------+
Means | 130 | 32 | 28 |374.5| | | 25.101|
------+-------+---------+-------+-----+-------+-------+-------+
The boat is 140 ft. long, and fitted with twin screws driven by compound
engines, one pair to each propeller. These engines are of the usual type,
constructed by Messrs. Yarrow. Each has two cylinders with cranks at 90 deg..
The framing, and, indeed, every portion not of phosphor-bronze or gun
metal, is of steel, extraordinary precautions being taken to secure
lightness. Thus the connecting rods have holes drilled through them from
end to end. The low pressure cylinders are fitted with slide valves. The
high pressure valves are of the piston type, all being worked by the
ordinary link motion and eccentrics. The engine room is not far from the
mid length of the boat, and one boiler is placed ahead and the other
astern of it. Each boiler is so arranged that it will supply either
engine or both at pleasure. The boat has therefore two funnels, one
forward and the other aft, and air is supplied to the furnaces by two
fans, one fixed on the forward and the other on the aft bulkhead of the
engine room.
The fan engines have cylinders 51/2 in. diameter and 31/2 in. stroke, and
make about 1,100 revolutions per minute when at full speed, causing a
plenum in the stokeholes of about 6 in. water pressure. Double steam
steering gear is fitted, for the forward and aft rudder respectively, and
safety from foundering is provided to an unusual degree by the
subdivision of the hull into numerous compartments, each of which is
fitted with a huge ejector, capable of throwing overboard a great body of
water. A body of water equal to the whole displacement of the boat can be
discharged in less than seven minutes. There is also a centrifugal pump
provided, which can draw from any compartment. The circulating pump is
not available, because it has virtually no existence, a very small pump
on the same shaft as the centrifugal being used merely to drain the
condensers. These last are of copper, cylindrical, and fitted with pipes
through which a tremendous current of water is set up by the passage of
the boat through the sea. Thus the space and weight due to a circulating
pump is saved and complication avoided. The air and feed pumps are
combined in one casting let into the engine room floor, quite out of the
way, and worked by a crank pin in a small disk on the forward end of the
propeller shaft. This is an admirable arrangement, and works to
perfection.
The armament of the boat consists of two torpedo tubes in her bows, and a
second pair set at a small angle to each--Yarrow's patent--carried aft on
a turntable for broadside firing. There are also two quick firing 3 lb.
guns on her deck. The conning tower forward is rifle proof, and beneath
it and further forward is fixed the steering engine, and a compressing
engine, by which air is compressed for starting the torpedoes overboard
and for charging their reservoirs. A small dynamo and engine are also
provided for working a search light, if necessary. The accommodation
provided for the officers and crew is far in advance of anything hitherto
found on board a torpedo boat.
The weather on the morning of Thursday, April 14, was anything rather
than that which would be selected for a trial, or indeed any, trip on the
Thames. At 11 A.M., the hour at which the boat was to leave Messrs.
Yarrow's yard, Isle of Dogs, the wind was blowing in heavy squalls from
the northeast, accompanied by showers of snow and hail. The Italian
government was represented by Count Gandiani and several officers and
engineers. In all there were about thirty-three persons on board. The
displacement of the vessel was as nearly as might be 97 tons. A start was
made down the river at 11:15 A.M., the engines making about 180
revolutions per minute, and the boat running at some 111/2 or 12 knots.
During this time the stokehole hatches were open, but the fans were kept
running at slow speed to maintain a moderate draught. The fuel used
throughout the trip was briquettes made of the best Welsh anthracite
worked up with a little tar. The briquettes were broken up to convenient
sizes before being put in the bunkers. This fuel is not of so high
evaporative efficiency as Nixon's navigation coal, but it is more
suitable for torpedo boat work, because it gives out Very little dust,
while the coal in closed stokeholes half smothers the firemen. Watering
only partially mitigates the evil. Besides this, the patent fuel does not
clinker the tube ends--a matter of vital importance.
During the run down to Gravesend, the small quantity of smoke given out
was borne down and away from the tops of the funnels by the fierce head
wind, and now and then a heavy spray broke on the bows, wetting
everything forward. In the engine room preparations were made for taking
indicator diagrams. No attempt was made to drive the boat fast, because
high speeds are prohibited by the river authorities on account of the
heavy swell set up.
The measured mile on the Lower Hope is on the southern bank of the river,
about three miles below Gravesend. Just as the boat passed the town, in
the midst of a heavy rain squall, the stokehole hatches in the deck were
shut, and the dull humming roar of the fans showed that the fires were
being got up. The smoke no longer rose leisurely from the funnels. It
came up now with a rush and violence which showed the powerful agency at
work below. A rapid vibrating motion beneath the feet was the first
evidence that the engines were away full speed. As the boat gathered way
she seemed to settle down to her work, and the vibration almost ceased.
The measured mile was soon reached, and then in the teeth of the
northeaster she tore through the water. The tide and wind were both
against her. Had the tide and wind been opposed, there would have been a
heavy sea on. As it was, there was quite enough; the water, breaking on
her port bow, came on board in sheets, sparkling in the sun, which, the
rain squall having passed, shone out for the moment. As the wind was
blowing at least thirty miles an hour, and the boat was going at some
twenty-six miles an hour against it, the result was a moderate hurricane
on board. It was next to impossible to stand up against the fury of the
blast without holding on. The mile was traversed in less than 21/2 minutes,
however; but the boat had to continue her course down the river for
nearly another mile to avoid some barges which lay in the way, and
prevented her from turning. Then the helm was put over, and she came
round. There was no slacking of the engines, and astern of her the water
leaped from her rudder in a great upheaved, foaming mass, some 7 ft. or 8
ft. high. Brought round, she once more lay her course. This time the wind
was on her starboard quarter, or still more nearly aft. The boat went
literally as fast as the wind, and on deck it was nearly calm. The light
smoke from the funnels, no longer beaten down by wind, leaped up high
into the air. Looking over the side, it was difficult to imagine that the
boat was passing through water at all. The enormous velocity gave the
surface of the river the appearance of a sheet of steel for 1 ft. or more
outside the boat. Standing right aft, the sight was yet more remarkable.
Although two 6 ft. screws were revolving at nearly 400 revolutions per
minute almost under foot, not a bubble of air came up to break the
surface. There was no wave in her wake; about 70 ft. behind her rose a
gentle swelling hill.
Her wake was a broad smooth brown path, cut right through the rough
surface of the river. On each side of this path rose and broke the angry
little seas lashed up by the scourging wind. Along the very center of the
brown track ran a thin ridge of sparkling foam, some 2 ft. high and some
20 ft. long, caused by the rudder being dragged through the water. There
was scarcely any vibration. The noise was not excessive. A rapid whirr
due to the engines, and a rythmical clatter due to the relief valve on
one of the port engine cylinders not being screwed down hard enough, and
therefore lifting a little in its seat at each stroke, made the most of
it. The most prominent noise perhaps was the hum of the fans. Standing
forward, the deck seems to slope away downward aft, as indeed it does,
for it is to be noted that at these high speeds the forefoot of the boat
is always thrown up clean out of the water--and the whole aspect of the
boat: the funnels vomiting thin brown smoke, and occasionally, when a
fire door is opened, a lurid pillar of flame for a moment; the whirr in
the engine room; the dull thunder of the fans, produce an impression on
the mind not easily expressed, and due in some measure no doubt to the
exhilaration caused by the rapid motion through the air.
The best way to convey what we mean is to say that the whole craft seems
to be alive, and a perfect demon of energy and strength. Many persons
hold that a torpedo boat is likely to be more useful in terrifying an
enemy than in doing him real harm, and we can safely say that the captain
of an ironclad who saw half a dozen of these vessels bearing down on him,
and did not wish himself well out of a scrape, has more nerve than most
men.
The second mile was run in far less time than that in which what we have
written concerning it can be read, and then the boat turned again, and
once more the head wind with all its discomforts was encountered. Events
repeated themselves, and so at last the sixth trip was completed, and the
boat proceeded at a leisurely pace back again to Poplar. Mr. Crohn,
representing Messrs. Yarrow on board, and all concerned, might well feel
satisfied. We had traveled at a greater speed than had ever before been
reached by anything that floats, and there was no hitch or impediment or
trouble of any kind.
The Italian government may be congratulated on possessing the two fastest
and most powerful torpedo boats in the world. We believe, however, that
Messrs. Yarrow are quite confident that, with twin screw triple expansion
engines, they can attain a speed of 26 knots an hour, and we have no
reason to doubt this.--_The Engineer._
* * * * *
RESERVOIR DAMS.
[Footnote: Paper, with slight abbreviation, read by Mr. David Gravell,
Assoc. M. Inst. C.E., before the Society of Civil and Mechanical
Engineers. The paper brings together in a convenient form the sections
and salient facts concerning many dams. It was illustrated by numerous
diagrams, from which our engravings have been prepared.--_The Engineer._]
By DAVID GRAVELL.
The construction of dams, in some form or other, may probably rank among
the very earliest of engineering works. Works of this character are not
infrequently referred to in the accounts of the earliest historians; but
it is to be feared that they are not always perfectly trustworthy. The
subscribers to the Mudie of the period had to be considered, and their
taste for the marvelous was probably not much inferior to that of our own
day. When, therefore, Herodotus describes the reservoir of Moeris as
formed for the control of the river floods of Nile-nourished Egypt, and
of another constructed by Nebuchadnezzar at Sippara, of 140 miles in
circumference, we must make allowances. But there is no question as to
the existence in the East at the present day, and especially in India and
Ceylon, of the remains of what may correctly be termed stupendous works;
and the date of the construction of which, as regards India, is in many
cases prehistoric. In Spain also the Moors, whose occupation of the
peninsula terminated in the thirteenth century, have left reservoir dams
of great magnitude, situated mostly in the south-eastern provinces of
Murcia and Alicante, and many of which are still serviceable.
In India and Ceylon the greater number of the ancient dams or bunds are
now in ruins, and this can occasion but little surprise, considering the
meteorological condition of these countries. In Ceylon, for instance, the
whole rainfall of the year occurs within a period of six to eight weeks,
and often amounts to as much as 12 in. in the twenty-four hours, and has
been known, comparatively recently, to reach nearly 19 in., the latter an
amount only 2 in. or 3 in. less than the average rainfall of Lincolnshire
for the whole year. In London it is only 25 in. and in the wettest
district in Great Britain, viz., Cumberland, averages not more than 70
in. per annum.
The rainfall in Bombay is from 80 in. to 100 in. per annum, and
throughout India may be taken as from 50 in. to 130 in., varying, as is
the general rule, in direct ratio with the altitude, and limited to a few
weeks in the year. Notwithstanding this, there still exist in the Madras
Presidency a not inconsiderable number of ancient bunds which serve their
intended purpose at the present day as well as ever. Slight mistakes did
occasionally occur, as they ever will till no more dams are wanted, as is
proved by the remains of some works in Ceylon, where the failure was
evidently due to error, possibly due to the instruments being out of
adjustment, as their base is at a higher level than the bed of the stream
at the point where water from the latter was to be diverted to afford the
supply.
Among the most remarkable of these ancient works is the Horra-Bera tank,
the bund of which is between three and four miles in length and from 50
to 70 ft. in height, and although now in ruins would formerly impound a
reservoir lake of from eight to ten miles long and three to four miles
broad. There is also the Kala-Weva tank, with a bund of twelve miles in
length, which would, if perfect, create a lake of forty miles in
circumference. Both of these ruined works are situated in Ceylon. The
third embankment of a similar character is that of the Cummum tank,
situated in the Madras Presidency, and which, though ranking among the
earliest works of Hindoo history, is still in such a condition as to
fulfill its original intention. The area of the reservoir is about
fifteen square miles, the dam about 102 ft. high, with a breadth at the
crest of 76 ft., and of the section shown in the diagram.
The by-wash is cut in the solid rock altogether clear of the dam; the
outlet culverts, however, are carried under the bank. We will now
consider generally the methods employed in determining the site,
dimensions, and methods of construction of reservoir dams adapted to the
varying circumstances and requirements of modern times, with a few
references to some of the more important works constructed or in
progress, which it will be endeavored to make as concise and burdened
with as few enumerations of dimensions as possible.
The amount of the supply of water required, and the purposes to which it
is to be applied, whether for household, manufacturing, or irrigation
uses, are among the first considerations affecting the choice of the site
of the reservoir, and is governed by the amount of rainfall available,
after deducting for evaporation and absorption, and the nature of the
surface soil and vegetation. The next important point is to determine the
position of the dam, having regard to the suitability of the ground for
affording a good foundation and the impoundment of the requisite body of
water with the least outlay on embankment works.
It has been suggested that the floods of the valley of the Thames might
be controlled by a system of storage reservoirs, and notice was
especially drawn to this in consequence of the heavy floods of the winter
of 1875. From evidence given before the Royal Commission on Water Supply,
previous to that date it was stated that a rainfall of 1 in. over the
Thames basin above Kingston would give, omitting evaporation and
absorption, a volume of 53,375,000,000 gallons. To prevent floods, a
rainfall of at least 3 in. would have to be provided against, which would
mean the construction of reservoirs of a storage capacity of say
160,000,000,000 gallons. Mr. Bailey Denton, in his evidence before that
commission, estimated that reservoirs to store less than one tenth that
quantity would cost L1,360,000, and therefore a 3 in. storage as above
would require an outlay of, say, L15,000,000 sterling; and it will be
seen that 3 in. is by no means too great a rainfall to allow for, as in
July of 1875, according to Mr. Symons, at Cirencester, 3.11 in. fell
within twenty-four hours. Supposing serious attention were to be given to
such a scheme, there would, without doubt, be very great difficulty in
finding suitable situations, from an engineering and land owner's point
of view, for the requisite dams and reservoir areas.
In Great Britain and many European countries rain gauges have been
established at a greater or less number of stations for many years past,
and data thereby afforded for estimating approximately the rainfall of
any given district or catchment basin. The term "watershed" is one which
it appears to me is frequently misapplied; as I understand it, watershed
is equivalent to what in America is termed the "divide," and means the
boundary of the catchment area or basin of any given stream, although I
believe it is frequently made use of as meaning the catchment area
itself. When saying that the rain gauges already established in most of
the older civilized countries afford data for an approximate estimate
only, it is meant that an increase in the number of points at which
observations are made is necessary, previous to the design of a reservoir
dam on the catchment area above, the waters of which are proposed to be
impounded, and should be continuous for a series of five or six years,
and these must be compared with the observations made with the old
established rain gauges of the adjacent district, say for a period of
twenty years previously, and modified accordingly. This is absolutely
necessary before an accurate estimate of the average and maximum and
minimum rainfall can be arrived at, as the rainfall of each square mile
of gathering ground may vary the amount being affected by the altitude
and the aspect as regards the rainy quarter.
But this information will be of but little service to the engineer
without an investigation of the loss due to evaporation and absorption,
varying with the season of the year and the more or less degree of
saturation of the soil; the amount of absorption depending upon the
character of the ground, dip of strata, etc., the hydrographic area
being, as a rule, by no means equal to the topographic area of a given
basin. From this cursory view of the preliminary investigations necessary
can be realized what difficulties must attend the design of dams for
reservoirs in newly settled or uncivilized countries, where there are no
data of this nature to go on, and where if maps exist they are probably
of the roughest description and uncontoured; so that before any project
can be even discussed seriously special surveys have to be made, the
results of which may only go to prove the unsuitability of the site under
consideration as regards area, etc. The loss due to evaporation,
according to Mr. Hawksley, in this country amounts to a mean of about 15
in.; this and the absorption must vary with the geological conditions,
and therefore to arrive at a satisfactory conclusion regarding the amount
of rainfall actually available for storage, careful gaugings have to be
made of the stream affected, and these should extend over a lengthened
period, and be compounded with the rainfall. A certain loss of water, in
times of excessive floods, must, in designing a dam, be ever expected,
and under favorable conditions may be estimated at 10 per cent. of the
total amount impounded.
As regards the choice of position for the dam of a reservoir, supposing
that it is intended to impound the water by throwing an obstruction
across a valley, it may be premised that to impound the largest quantity
of water with the minimum outlay, the most favorable conditions are
present where a more or less broad valley flanked by steep hills suddenly
narrows at its lower end, forming a gorge which can be obstructed by a
comparatively short dam. The accompanying condition is that the nature of
the soil, i.e., the character, strata, and lie of the rock, clay, etc.,
as the case may be, is favorable to assuring a good foundation. In Great
Britain, as a rule, dams for reservoirs have been constructed of
earthwork with a puddle core, deemed by the majority of English engineers
as more suitable for this purpose than masonry.
Earthwork, in some instances combined with masonry, was also a form usual
in the ancient works of the East, already referred to; but it would
appear from the experience of recent years that masonry dams are likely
to become as common as those of earthwork, especially in districts
favorable to the construction of the former, where the natural ground is
of a rocky character, and good stone easily obtained.
As to the stability of structures of masonry for this purpose, as
compared with earthwork, experience would seem to leave the question an
open one. Either method is liable to failure, and there certainly are as
many cases on record of the destruction of masonry dams as there are of
those constructed of earthwork, as instanced in Algeria within the past
few years. As regards masonry dams, the question of success does not seem
so much to depend upon their design, as far as the mere determination of
the suitable profile or cross section is concerned, as that has been very
exhaustively investigated, and fairly agreed upon, from a mathematical
point of view, but to be principally due to the correctness of the
estimate of the floods to be dealt with, and a sufficient provision of
by-wash allowed for the most extreme cases; and, lastly, perhaps the most
important of all, the securing a thoroughly good foundation, and a
careful execution of the work throughout.
These remarks equally apply to earthwork dams, as regards sufficient
provision of by-wash, careful execution of work, and security of
foundation, but their area of cross section, supposing them to be
water-tight, on account of the flatness of their slopes and consequent
breadth of base, is, of course, far in excess of that merely required for
stability; but in these latter, the method adopted for the water supply
discharge is of the very greatest importance, and will be again referred
to.
Before commencing the excavation for the foundations of a dam, it is most
essential that the character of the soil or rock should be examined
carefully, by sinking a succession of small shafts, not mere borings,
along the site, so that the depth to which the trench will have to be
carried, and the amount of ground water likely to be encountered, can be
reliably ascertained, as this portion of the work cannot be otherwise
estimated, and as it may bear a very large proportion of the total
expense of construction, and in certain cases may demonstrate that the
site is altogether unsuitable for the proposed purpose.
The depth to which puddle trenches have been carried, for the purpose of
penetrating water-bearing strata, and reaching impenetrable ground, in
some cases, has been as much as 160 ft. below the natural surface of the
ground, and the expense of timbering, pumping, and excavation in such an
instance can be easily imagined. This may be realized by referring to
Fig. 4, giving a cross-section of the Yarrow dam, in which the bottom of
the trench is there only 85 ft. below the ground surface. In the Dale
Dyke dam, Fig. 2, the bottom of the trench was about 50 ft. below the
ground surface.
There is one other point which should be mentioned in connection with the
form of the base of the puddle trench--that instead of cutting the bottom
of the trench at the sides of the valley in steps, it should be merely
sloped, so that the puddle, in setting, tends to slide down each inclined
plane toward the bottom of valley, thereby becoming further compressed;
whereas, should the natural ground be cut in steps, the puddle in setting
tends to bulge at the side of each riser, as it may be termed, and so
cause fissures. It will be noticed that the slopes of these earthwork
dams vary from 7 to 1 to 2 to 1.
The depths to which some puddle trenches are carried has been objected to
by some engineers, and among them Sir Robert Rawlinson, as excessive and
unnecessary, and, in the opinion of the latter, the same end might be
obtained by going down to a depth say of 30 ft. only, and putting in a
thick bed of concrete, and also carrying up the concrete at the back of
the puddle trench, with a well for collecting water, and a pipe leading
the same off through the back of the dam to the down stream side. An
arrangement of this kind is shown in the Yarrow dam, Fig. 4.
The thickness of the puddle wall varies considerably in the different
examples given in the diagrams before you, a fair average being the Row
bank of the Paisley Water Works, Fig. 6; and although in instances of
dams made early in the century, such as the Glencorse dam--Fig. 5--of the
Edinburgh Water Works, the puddle was of very considerable thickness, and
it would appear rightly so. This practice does not seem to have been
followed in many cases, as, for instance, again referring to the Dale
Dyke dam, Fig. 2, where the thickness of the top was only 4 ft., with a
batter of 1 in 16 downward, giving a thickness of 16 ft. at the base. For
a dam 95 ft. in height this is very light, compared with that of the
Vehui dam at Bombay, of which the engineer was Mr. Conybeare--Fig.
7--where the puddle wall is 10 ft. wide at the top, with a batter
downward of 1 in 8, the Bann reservoir--Fig. 8--of Mr. Bateman's design,
where the puddle is 8 ft. broad at the top, and other instances. The same
dimension was adopted for the puddle wall of the Harelaw reservoir, at
Paisley, by Mr. Alexander Leslie, an engineer of considerable experience
in dam construction.
There appears to be a question as to what the composition of puddle
should be, some advocating a considerable admixture of gravel with clay.
There is no doubt that clay intended for puddle should be exposed to the
weather for as long previous to use as possible, and subject to the
action of the air at any rate, of sunshine if there be any, or of frost.
When deposited in the trench, it should be spread in layers of not more
than 6 in. in thickness, cut transversely in both directions, thoroughly
watered, and worked by stamping.
The position of the puddle wall is, as a rule, in the center of the bank
and vertical; but laying a thickness of puddle upon the inner or up
stream slope, say 3 ft. thick, protected by a layer of gravel and
pitching, has been advocated as preventing any portion of the dam from
becoming saturated. There are, however, evident objections to this
method, as the puddle being comparatively unprotected would be more
liable to damage by vermin, such as water rats, etc.; and in case of the
earthwork dam at the back settling, as would certainly be the case,
unless its construction extended over a very lengthened period, the
puddle would be almost certain to become fissured and leaky; in addition,
the comparative amounts of puddle used in this manner, as compared with
the vertical wall, would be so much increased. With the puddle wall in
the position usually adopted, unequal settlement of the bank on either
side is less liable to affect the puddle, being vertical.
It would be interesting to refer to the embankment of the Bann, or Lough
Island Reavy reservoir, Fig. 8, designed by Mr. Bateman, now nearly fifty
years ago, where a layer of peat was adopted both on the slope, 15 in.
thick, and in front or on the up stream side of the puddle wall, 3 ft.
thick. The object was, that should the puddle become fissured and leaky,
the draught so created would carry with it particles of peat, which would
choke up the cracks and so reduce the leakage that the alluvial matter
would gradually settle over it and close it up. On the same diagram will
be noticed curved lines, which are intended to delineate the way in which
the earthwork of the embankment was made up. The layers were 3 ft. in
thickness, laid in the curved layers as indicated.
It is a moot question whether, in making an earthwork embankment,
dependence, as far as stanchness is concerned, should be placed upon the
puddle wall alone or upon the embankments on either side, and especially
upon the up-stream side in addition. Supposing the former idea prevails,
then it can be of little moment as to how or of what material the bank on
either side is made up--whether of earth or stone--placed in thin layers
or tipped in banks of 3 ft. or 4 ft. high; but the opinion of the
majority of engineers seems to be in favor of making the banks act not
merely as buttresses to the puddle wall, and throwing the whole onus, as
it may be termed, of stanchness upon that, but also sharing the
responsibility and lessening the chances of rupture thereby. But to
insure this, the material must be of the very best description for the
purpose. Stones, if allowed at all--and in the author's opinion they
should not be--should be small, few, and far between. Let those that are
sifted out be thrown into the tail of the down stream slope. They will do
no harm there, but the layers of earth must not approach 3 ft. in
thickness nor 1 ft.--the maximum should be six in., and this applies also
to the puddle. Let the soil be brought on by say one-horse carts, spread
in six inch layers, and well watered. The traffic of the carts will
consolidate it, and in places where carts cannot traverse it should be
punned. In the Parvy reservoir dam a roller was employed for this
purpose. It comprised a small lorry body holding about a yard and a half
of stone, with two axles, on each of which was keyed a row of five or six
wheels.
At the Oued Meurad dam, in Algeria, 95 ft. high, constructed about 23
years ago, the earthwork layers were deposited normal to the outer slope,
and as the bank was carried up the water was admitted and allowed to rise
to near the temporary crest, and as soon as the bank had settled, the
earthwork continued another grade, and the same process repeated.
It was the practice until comparatively recently to make the discharge
outlet by laying pipes in a trench under the dam, generally at the lowest
point in the valley, or constructing a culvert in the same position and
carrying the pipes through this, and in the earlier works the valves or
sluices regulating the outflow were placed at the tail of the down stream
bank, the pipes under the bank being consequently at all times subject to
the pressure of the full head of the water in the reservoir. An instance
of the first mentioned method is afforded by the Dale Dyke reservoir,
Fig. 2, where two lines of pipes of 18 in. diameter were laid in a trench
excavated in the rock and resting upon a bed of puddle 12 in. in
thickness, and surrounded by puddle; the pipes were of cast iron, of the
spigot and faucet type, probably yarned and leaded at the joints as
usual, and the sluice valves were situated at the outer end of the pipes.
As the failure of this embankment was, as we all know, productive of such
terrible consequences, it may be of interest to enter a little more fully
into the details of its construction. It was situated at Bradfield, six
or seven miles from Sheffield, and at several hundred feet higher level.
Its construction was commenced in 1858, the puddle trench was probably
taken down to a depth of 40 ft. to 50 ft., a considerable amount of water
being encountered. This trench was 15 ft. to 20 ft. broad at the top, and
of course had to be crossed by the before mentioned line of pipes; and
although the trench was filled with puddle, and the gullet cut in the
rock already mentioned for carrying the pipes under the site of the dam
was "padded" with a layer of 12 in. of puddle, we can imagine that the
effect of the weight of the puddle wall and bank upon this line of pipes
would be very different at the point where they crossed the puddle trench
to what it would be where they were laid in the rock gullet and partially
protected from pressure by the sides of the latter. At the trench
crossing there would be a bed of puddle 50 ft. in thickness beneath the
pipe, in the gullet a bed of 1 ft. in thickness. So much as regards the
laying of the pipes.
The embankment had scarcely been completed when, on March 11, 1864, a
storm of rain came on and nearly filled it up to the by-wash, when the
bank began slowly to subside. The engineer was on the crest at the very
time, and remained until the water was running over his boots; he then
rushed down the other slope and was snatched out of the way as the bank
burst, and the whole body of water, about 250,000,000 gallons, rushed out
through the trench, carrying with it in the course of about twenty
minutes 92,000 cubic yards, or say one fourth of the total mass of
earthwork, causing the death of 250 human beings, not to mention cattle,
and destruction of factories, dwellings, and bridges, denuding the rock
of its surface soil, and, as it were, obliterating all the landmarks in
its course. The greatest depth of the bank from ground level to crest was
95 ft., the top width 12 ft., and the slopes, both on the up stream and
down stream sides, 21/2 to 1, and the area of the reservoir 78 acres.
Mr.--now Sir Robert--Rawlinson, together with Mr. Beadmore, were called
in to make a report, to lay before Parliament, upon this disaster; and
having made a careful examination of the ruins, and taken evidence, they
were of opinion that the mode of laying the pipes, and in such an
unprotected way, was faulty, and that subsidence of the pipes probably
occurred at the crossing of the puddle trench. A fissure in the puddle
was created, affording a creep for the water, which, once set up, would
rapidly increase the breach by scour; and this event was favored by the
manner in which the bank had been constructed and the unsuitability of
the material used, which, in the words of one engineer, had more the
appearance of a quarry tip than of a bank intended to store water. This
opinion of the cause of failure was, however, not adopted universally by
engineers, the line of pipes when examined being found to be, although
disjointed, fairly in line; and there having occurred a land slip in the
immediate neighborhood, it was suggested that the rupture might be caused
by a slip also having taken place here, especially as the substratum was
of flagstone rock tilted at a considerable angle. The formation was
millstone grit. This catastrophe induced an examination to be made of
other storage reservoir dams in the same district, and a report on the
subject was presented to Parliament by Sir Robert Rawlinson.
[Illustration: TYPICAL MASONRY AND EARTHWORK DAMS OF THE WORLD.]
The dam of Stubden reservoir, of the Bradford water supply, also on the
millstone grit, was constructed about 1859, and caused considerable
anxiety for a length of time, as leakage occurred in the culvert carrying
the pipes, under the embankment at a point a short distance on the down
stream side of the puddle trench. This was repaired to some extent by
lining with cast iron plates; and an entirely independent outlet was made
by driving a curved tunnel into the hill side clear of the ends of the
dam and lining it with cast iron plates. In this tunnel was then laid the
main of 2 ft. diameter, and as the original culvert again became leaky,
the water had to be lowered, the old masonry pulled out, and the space
filled in with puddle.
The Leeming compensation reservoir of the same water supply, with a dam
of 50 ft. in height, and culvert outlet, had to be treated somewhat in
the same manner, as, although the reservoir had never been filled with
water, in 1875, when it was examined previous to filling, it was found
that the culvert was cracked in all directions; and it was deemed best to
fill it up with Portland cement concrete, and drive a tunnel outlet
through the hill side, as described in the case of the Stubden reservoir.
The Leeshaw dam, which was being constructed at that time upon the same
lines, viz., with culvert outlet under the dam, was, at the advice of Sir
Robert Rawlinson, altered to a side tunnel outlet clear of the dam.
Some years previous to the failure of the Dale Dyke reservoir there
occurred, in 1852, a failure of a similar character--though, as far as
the author is aware, unattended by such disastrous results--at the
Bilberry reservoir at Holmfirth, near Huddersfield, which had never been
filled previous to the day of its failure, and arose from the dam having
sunk, and being allowed to remain at a level actually below that of the
by-wash; so that when the storm occurred, the dam was topped and
destroyed. An after examination proved that the bank was badly
constructed and the foundation imperfect.
Besides the above instances, there have been numerous failures within
recent times of earthwork dams in Spain, the United States, Algeria, and
elsewhere, such as that which occurred at Estrecho de Rientes, near
Lorca, in Murcia, where a dam 150 ft. high, the construction of which for
irrigation purposes was commenced in 1755 and completed in 1789, was
filled for the first time in February, 1802, and two months later gave
way, destroying part of the town of Lorca and devastating a large tract
of the most fertile country, and causing the death of 600 people. The
immediate cause of failure in this case the author has been unable to
ascertain. In Algeria the Sig and Tlelat dams were destroyed in 1865; and
in the United States of America, at Williamsburg, Hampshire Co.,
Massachusetts, in 1874, an earthwork dam gave way, by which 159 lives
were lost and much damage done to property. In another case, viz., that
of the Worcester dam, in the United States of America--impounding a
volume of 663,330,000 gallons, and 41 ft. high, 50 ft. broad at the
crest, and formed with a center wall of masonry, with earthwork on each
side--which gave way in 1875, four years after its completion; here, as
in almost all other instances of failure, the leakage commenced at a
point where the pipes traverse the dam. In this case they were carried in
a masonry culvert, and the leak started at about 20 ft. on the up stream
side of the central wall. The opinion of Mr. McAlpine as to the cause of
failure, which agrees with that of the most eminent of our own water
engineers, was to the effect that "earthen dams rarely fail from any
fault in the artificial earthwork, and seldom from any defect in the
natural soil. The latter may leak, but not so as to endanger the dam. In
nine tenths of the cases, the dam is breached along the line of the water
outlet passages."
The method of forming the discharge outlet by the construction of a
masonry culvert in the open has no doubt many advantages over that of
tunnel driving through the hill side clear of the dam, permitting as it
does of an easy inspection and control of the work as it proceeds; but a
slight leakage in the instance of a side tunnel probably means nothing
more than the waste of so much water, whereas in the case of the culvert
traversing the site of the bank, the same amount or less imperils the
stability of the bank, and in ninety-nine cases out of a hundred would,
if not attended to, sooner or later be the cause of its destruction. I
think the majority will therefore agree that the method of discharge
outlets under the site of embankments should not be tolerated where it is
possible to make an outlet in the flank of the hill, to one side, and
altogether clear of the dam.
At Fig. 9 is a diagram of the Roundwood dam of the Vartry Water Works,
supplying Dublin, which is a fair specimen of the class of earthwork dam
with the outlet pipes carried in a culvert under the embankment, and
which, perhaps, is one of the most favorable specimens of this method of
construction, as the inlet valves are on the up stream of the dam, and
consequently when necessary the water can be cut off from the length of
pipes traversing the dam. A short description will be given. This dam is
66 ft. high at the deepest point and 28 ft. wide at the crest, having to
carry a public road. The slope on the inner face is 3 to 1, and on the
outer 21/2 to 1. The by-wash is 6 ft. below the crest, which is about the
average difference. The storage capacity of the reservoir is
2,400,000,000 gallons, or sufficient for 200 days' supply to the city.
The puddle wall is 6 ft. wide at the top and 18 ft. at ground level, the
bottom of the puddle trench about 40 ft. below the surface of the ground.
The culvert was formed by cutting a gullet 14 ft. wide with nearly
vertical sides through the rock, and covering it with a semicircular arch
4 ft. in thickness. Through this tunnel are laid a 33 in. and 48 in.
main; the former for the water supply, and the latter for scouring or for
emptying the reservoir on an emergency. There is a plugging of brickwork
in cement under the center of the dam in the line of the puddle wall, and
then stop walls built at the end of the plugging, projecting 25 ft.
beyond the sides of the culvert and 8 ft. above, the space between them
being filled up with cement concrete tied into the rock, and on this the
puddle wall rests. This bank, like almost all others pierced by outlet
pipes or culverts, was not destined to be perfect. In 1867, four years
after the completion, spurts of water showed themselves in the culvert
in front of the puddle wall, which began to settle, and the water had to
be drawn off to admit of repairs. Diagram No. 10 shows a structure of a
different character to any of these already described. This character of
work is adopted on the North Poudre Irrigation Canal, in N.E. Colorado.
Timber is there plentiful, and a dam of this character can be rapidly
constructed, although probably not very durable, owing to liability to
decay of timber. That represented is about 25 ft. high.
The author has now concluded the consideration of earthwork dams, and
proposes making a few remarks upon those of masonry or concrete, with
reference to some of the most important, as shown on the diagrams. Their
stability, unlike those of earthwork, may be considerably increased where
the contour and nature of the ground is favorable by being curved in
plan, convex toward the water, and with a suitable radius. They are
especially suitable for blocking narrow rocky valleys, and as such
situations must, from the character of the ground, be liable to sudden
and high floods, great care is necessary to make sufficient provision for
overflow.
When of masonry, the stones should be bonded, not merely as they would be
in an ordinary vertical wall, where the direction of the stress is
perpendicular, but each course should be knit in with that above and
below it in a somewhat similar manner to what is termed "random" work.
And lastly, if hydraulic mortar be used, a sufficient time should elapse
after construction before being subjected to strain, or in other words,
before water is allowed to rise in the reservoir. For this latter reason,
and also the liability to damage by sudden floods during the progress of
the works, dams of Portland cement concrete, on account of their quick
consolidation, possess advantages over those of hydraulic masonry apart
from the necessity in the latter instance of constant supervision to
prevent "scamping" by leaving chinks and spaces vacant, especially where
large masses of stone or Cyclopean rubble are used.
Again, should the dam be drowned by flood during its erection, no harm
would accrue were it composed of Portland cement concrete, whereas should
it be of hydraulic mortar masonry, the wall would probably be destroyed
or, at all events, considerably injured by the mortar being washed out of
the joints. Portland cement, however, is only suitable for situations
where the foundation is absolutely firm, as, should there be the
slightest settlement, fissures would certainly be produced.
As regards foundations, the dam of the Puentes reservoir in Spain is
somewhat remarkable--see Fig. 12. Its height is 164 ft., and the profile
or cross section is of precisely the same character as that of the
Alicante dam, the latter being 135 ft. in height, 65 ft. wide at the
crest, and 65 ft. at the base, and erected about 300 years ago. At the
Puentes dam the flanks of the valley were reliable, but, as must be
frequently the case in such situations, the bed of the valley was
composed to a great depth of gravel, _debris_, and shaky strata. The
difficulty was overcome by throwing an arch, or arches, across the
valley, the abutments being formed by the solid rock on each side, and
building the dam upon this arching and filling in below the latter down
to a sufficient depth with walling.
Bearing in mind the sudden and great floods to which dams constructed in
such situations must be subjected, and, if the valley be very narrow, the
probability that sufficient space at the side for a by-wash will be
difficult to obtain, it would seem reasonable that in the calculation for
their section allowance should be made for the possible condition of the
whole length of the dam being converted into a weir, over which the
waters may flow without risk of injury to the dam, to a depth of, say, at
least twice that ever probable.
The topping of dams by floods is not uncommon, and if the extra strain
thus induced has not been allowed for, their destruction is nearly
certain, as instanced in more than one case in Algeria, where, although
the average rainfall is only 15 in. yearly, a depth of 61/4 in., or more
than one-third of the annual total, has been known to fall in twenty-four
hours.
The Habra dam--see Fig. No. 13--completed in 1871, was destroyed by a
sudden flood of this kind in December, 1881. This reservoir, with a
storage capacity of 6,600,000,000 gallons, was intended for the
irrigation of a cultivated bordering on the Mediterranean and the storage
of floods. The height of the dam was 116.7 ft. and was provided with a
by-wash of 394 ft. in length, and outlets for irrigation formed by four
cast iron pipes of 311/2 in. diameter through the dam. It was composed of
rubble set in hydraulic mortar, the latter composed of two parts of sand
to one of hydraulic lime.
For getting rid of the large deposits of sand to which all reservoirs in
that country are liable, two scouring outlets were provided of the same
description as those in the old Moorish dams. The profile was calculated
from Delocre's formula, and was correct in this respect, supposing the
by-wash to have been sufficient. But as it was otherwise, and the flood
swept over the crest to the depth of about 3 ft., the enormous extra
strain thus induced overthrew the dam and caused the destruction of
several villages and the death of 209 persons. It must be mentioned that
when the reservoir was filling, the water percolated through the masonry,
giving the face wall the appearance of a huge filter, which at the time
was attributed to the porous nature of the sandstone used in
construction, but which more probably was due to the washing of the green
mortar out of the joints.
At the Hamiz dam, also in Algeria, the water was admitted in 1884, but it
showed immediately signs of weakness, so that the water had to be run out
and an immense retaining wall erected to strengthen the main dam. Algeria
seems to have been singularly unfortunate as regards the success of works
of this description. Water was admitted to the Cheurfas reservoir in
January, 1885, and it at once began to make its way through permeable
ground at one end of the dam. The flushing sluice in the deepest part of
the dam had become jammed, so that the pressure could not be relieved,
and in February 30 ft. length of the dam was carried away, causing a
flood in the river below. At some distance down stream was the Sig
reservoir. The flood rushing down, topped this dam by 18 ft. and
overthrew it also.
Allusion has been made to provision for scouring out sand and deposit,
especially in the dams of Algeria and of Spain. The amount of sand, etc.,
brought down by the floods is something enormous, and the question of the
best means of getting rid of it has occupied much attention. In the old
Moorish reservoirs the flushing gallery, piercing the lower part of the
dam, was closed by iron doors on the down stream face and blocked with
timber at the upper end. When required to be flushed out, laborers passed
through the gallery and broke down the timber barrier, the silt forming a
wall sufficiently thick to resist the pressure of the water for the time
being, and allow of the retreat of the Forlorn Hope--if the latter had
luck--before giving way.
One method adopted in Algeria, which has the advantage of permitting the
sediment to be utilized together with the irrigation, this sediment being
very fertilizing, is to pump air down through hose extending to the
bottom of the reservoir, the pumps being actuated by steam power or
turbine, and the sediment thus stirred up and run off with the water
through the irrigation pipes. As an example of one of the early types of
masonry dams in France, reference may be made to Fig. 13, on which is
shown an elevation and cross section of the Lampy dam, forming a large
reservoir for feeding the Languedoc canal.
I will now refer to some of the most notable masonry dams in existence,
commencing with France, where perhaps the finest is that known as the
Furens, in connection with the St. Etienne Water Works, constructed
between the years 1859-66, and designed by the engineers Graiff and
Grandchamps. It is curved in plan, struck with a radius of 828 ft. from a
center on the down stream side, and founded upon compact granite, the
footings being carried down to a depth of 3 ft. 3 in. below the surface
of the rock. It is of rubble masonry, in hydraulic mortar, carried up in
courses of 5 ft. in depth.
The height is 170 ft. on the up stream side and 184 ft. high on the lower
side, with a breadth of 9 ft. 8 in. at the crest and 110 ft. at the base,
and the cross section is so designed that the pressure is nearly constant
in all parts, and nowhere exceeds 93 lb. to the square inch--13,392 lb.
to the square foot. The contents is equal to 52,000 cubic yards of
masonry, and the cost of erection was L36,080. The capacity of the
reservoir is equal to 352,000,000 gallons.
The reservoir discharges into two tunnels (see Fig. 11), driven one above
the other through a hill into an adjacent valley. The lower tunnel
contains three cast iron pipes, with a masonry stopping of 36 ft. long.
Two of these pipes are 16 in. diameter, with regulating valves, and
discharge into a well, from whence the water can be directed for the town
supply or into the river. The third pipe, of 81/2 in. diameter, is always
open, and serves to remove any deposit in the reservoir, and to furnish a
constant supply for the use of manufacturers.
The author drew attention to the difference in the section of the Furens
dam, Fig. 11, as compared with that of Alicante, and of Puentes, which is
similar to the latter. These two last illustrate the ancient Moorish
type, and the former that of the present day. The Gileppe dam at
Verviers, in Belgium, Fig. 14, although quite recently erected, viz.,
between the years 1869 and 1875, differs very much from the Furens type,
in so far as it is of very much larger sectional area in proportion to
its height, but this is accounted for by the desire of the engineer, M.
Bodson, to overcome the opposition to its construction, and meet the
objections and combat the fears of those whose interests--and those
serious ones, no doubt--would be affected in the event of its rupture,
the body of water stored being 2,701,687,000 gallons, or about eight
times as much as the capacity of the Furens reservoir.
In addition to this, there was another reason, which was quite sufficient
in itself to account for the extra substantiality of the dam. This
reservoir is for supplying water to the cloth factories of Verviers, on
the Belgian-German frontier. It is curved in plan to a radius of 1,640
ft., with a length of 771 ft., and the additional strength of the
structure due to so flat a curve is probably slight.
It is built of rubble masonry, with ashlar facework, laid in hydraulic
mortar. The total amount of masonry is 325,000 cubic yards. There are two
weirs, at a level of 6 ft. below the crest, each 82 ft. wide. The total
height, including the foundations, which are carried down from 3 ft. to 5
ft. into the rock, is 154 ft., and the breadth of the crest, which
carries a road, is 49 ft. 3 in., and at the base 216 ft. The outlet pipes
are carried through tunnels, which are driven on the curve into the hill
side a considerable distance clear of each end of the dam.
Another very important structure is the Villar dam, Fig. 15, in
connection with the water supply of Madrid, and situated on the river
Lozoya. The storage capacity of this reservoir is very considerable,
viz., 4,400,000,000, or nearly thirteen times as great as that of Furens.
The height of the dam is 162 ft., with a breadth of 14 ft. 9 in. at the
crest. It is built on the curve to a radius of 440 ft., and the length of
the dam measured along the crest is 546 ft., of which 197 ft. is by-wash,
thus describing nearly one-fifth of a circle, and consequently well
designed to resist pressure. The dam is built of rubble masonry in
hydraulic mortar, and cost L80,556.
The Stony Creek lower reservoir dam of the Geelong water supply, Fig. 16,
colony of Victoria, is interesting as being constructed of concrete, in
the proportion of 1 to 81/2. Its erection occupied eighteen months, and
cost about L18,000. It is curved in plan to a radius of 300 ft., and the
greatest depth or head of water is 52 ft. 4 in. The width at the crest is
only 2 ft. 8 in., although surmounted by a heavy coping of bluestone 3
ft. 3 in. broad and 1 ft. 9 in. deep. There being no facility for making
a by-wash at the side, the center of the dam is dished to form a weir 30
ft. long. There are both outlet and scour pipes, and valves of 2 ft.
diameter, and the capacity of the reservoir is 143,145,834 gallons.
The Paramatta dam, in New South Wales, built of masonry in hydraulic
mortar, is another instance of a dam built on the curve, and which has
resisted a flood of water 4 ft. in depth over the crest; and in the case
of a dam of about 40 ft. high across the river Wyre, in connection with
the Lancaster Water Works, made of cement concrete in proportion of 4 to
1, there has, according to Mr. Mansergh, frequently been a depth of 5 ft.
of flow over it. This dam is built to a radius of 80 ft. only, and as it
measures 100 ft. along the crest, must include about the fifth of a
circle.
There now remain only two other examples of masonry dams, the first being
that in connection with the Liverpool water supply, and known as the
Vyrnwy dam, Fig. 17, this being thrown across a stream of that name in
North Wales. It is now under construction, and when completed will
impound an area of 1,115 acres.
The dam will be 1,255 ft. long, and formed of Cyclopean rubble set in
cement mortar, and the interstices or spaces between the large masses of
stone, which are rough hewn and not squared, are filled with cement
concrete. The proportion of the cement mortar is 21/2 to 1. These masses of
stone weigh from two to eight tons each, and it is expected that the wall
will be of a most solid description, as great care is being taken to fill
up all spaces. The face next to the water is cemented. The area of the
cross section shown on the diagram, which is at one of the deepest
points, is 8,972 square feet, and the height from foundation to flood
level is 129 ft., the breadth at the base being 117 ft. 9 in.
The existing dam of the New York water supply, Fig. 18, known as the
Croton reservoir, is shown on the diagram. Its capacity is 364,000,000
gallons and the area 279 acres. The height is 78 ft. and width at crest 8
ft. 6 in., and is built of masonry in hydraulic mortar. The face walls
are of stone laid in courses of 14 in. to 26 in., and are vertical on the
up stream side, and with a batter of 1 in 21/2 on the down. The hearting is
of concrete for a depth of 45 ft. from the top, and the remaining depth
is in Cyclopean rubble.
At Fig. 19 is shown the section of the Quaker Bridge dam, which when
completed will be the largest structure of the kind in existence. It is
situated on the Croton River, which is a tributary of the Hudson, about
four miles below the present Croton dam. The length will be 1,300 ft. and
the height 170 ft. above the river bed, or 277 ft. above the foundation.
The water by-wash is 7 ft. below the crest, and the dam is 26 ft. broad
at the crest and 216 ft. at the base. The capacity of the reservoir will
be 32,000,000,000 gallons, or nearly a hundred times as great as that of
Furens. The geological formation at the site is sienitic gneiss. The cost
of the dam is estimated at L500,000.
[Illustration: TYPICAL MASONRY AND EARTHWORK DAMS OF THE WORLD.]
The accompanying table gives the pressures to which various dams are
subjected, and it may be noted with regard to the weight of water,
generally assumed as 62.4 lb. per cubic foot, that it will, in some
districts, in time of flood, carry so much matter in suspension as to be
increased to as much as 75 lb. weight, or an addition of 20 per cent.,
which, it may be easily imagined, will affect the conditions of stability
very seriously.
TABLE OF MAXIMUM PRESSURES.
Lb. per sq. in.
Gileppe (Verviers). 88
Furens (St. Etienne). 93
Puentes. 112
De Ban. 113
St. Chamond. 114
Alicante. 154
Hamiz (Algeria)--failed. 157
Habra (Algeria)--failed. 185
A diagram comparing the section derived from Molesworth's formula and
those of Furens, Gileppe, Vyrnwy, and Quaker Bridge, is given at Fig. 20,
the limit of pressure assumed for the masonry being 93 lb. per square
inch, which is that of the Furens, the Gileppe being 88.
* * * * *
NEW DREDGING MACHINERY.
We illustrate the new dredger Ajax, recently built for Mr. Geo. F. Smith,
of Stockton, Cal.
The dredger has now been working for two weeks at Wakefield, and, we are
informed, is giving entire satisfaction; having been repeatedly timed to
be discharging clay at the rate of 220 cubic yards per hour.
[Illustration: THE NEW DREDGER AJAX.]
The Ajax is almost a duplicate of the last dredger designed by Mr. Ferris
for levee building on Roberts Island, with such modifications and
improvements as have suggested themselves in the two years it has been
working.
The hull, oval in plan, is 36 ft. 10 in. by 60 ft. over all; it has four
solid fore and aft bulkheads, and a well hole 5 x 12 ft. at one end for
the bucket ladder.
The main engine is 10 x 24, operating, by bevel gearing and a 31/2 in.
vertical shaft, a 4 sided upper tumbler with 21 in. sides. This engine
works also a gypsy shaft for swinging, and the conveyer that carries the
mud ashore. A steam hoist with 6 x 11 engines raises and lowers the
bucket ladder. The buckets, at 4 foot centers, have a struck capacity of
5 cubic feet, and are speeded to deliver from 18 to 20 a minute,
according to the character of the material being handled. They are of
boiler iron, with a 5 in. steel nosing. The links are of wrought iron,
with cast bushings. The lower tumbler is hexagonal, on a 4 in. shaft.
The conveyer, projecting 72 ft. from the center of the boat, consists of
a 5 ply rubber belt 36 in. wide; running over iron drums at each end and
intermediate iron friction rollers at 3 foot centers. Ratchet and pinion
on each side of conveyer ladder give means for taking up the slack of the
belt and adjusting the drums to maintain them parallel.
This conveyer is the important feature of the dredge. It is entirely
satisfactory in its working and delivers its material, as nearly as may
be, in a dry state upon the levee. It was feared the rubber belt would be
shortlived, but a 4 ply belt ran continuously for over two years on the
Roberts Island dredge before it needed replacing.
The boiler is of the marine type, 52 in. by 10 ft. 6 in., with 3 in.
tubes and 14 in. flues; and burns about 1,400 lb. of steam coal in a day
of 12 hours. There are three pumps aboard--a hand force pump for washing
boiler, a plunger pump for boiler feed, and an Evans steam pump to throw
a jet of water into the delivery hopper when digging in any very
tenacious material. All three are connected with the boiler.
Water tanks below deck serve to trim the boat and furnish a supply for
the boiler. The dredger cuts by swinging on a center spud 16 in. in
diameter, and moves forward from 8 to 10 ft. at each fleet.
The Roberts Island dredger, of which the Ajax is an improved copy,
handles steadily 700 yards per day of 12 hours, in the stiffest and most
tenacious clay in which it has been worked; and ranges from that average
to 1,500 yards per day in soft, peaty mud.
The Ajax was built by Farrington, Hyatt & Co., of the Stockton Iron
Works.
This type of dredger can be built for about $12,500, and we are informed
can be relied on for a monthly average of 26,000 yards in any material
met with in the overflowed lands near Stockton, delivered 50 ft. ashore,
at a height of 10 or 12 ft. above the ground line.--_Min. and Sci.
Press_.
* * * * *
THE FLEXIBLE GIRDER TRAMWAY.
This is an ingenious proposition for utilizing a modification of the wire
tramway system for overcoming obstacles (while retaining the ordinary
wire tramway or any light railway on other parts of the line), made by
Mr. Charles Ball, of London.
The flexible girder tramway is an improved system of constructing a
modification of the well known and extensively used rope or wire tramway,
and it is claimed that it will revolutionize the transport of the
products of industrial operations from the place of production to the
works or manufactory, railway station, shipping ports, or place of
consumption; and that in the result the introduction of the flexible
girder tramway will in many cases enable profits to be earned in
businesses which have hitherto been unremunerative. It is declared to be
at once simple, cheap, durable, and efficient. The improvement consists
in the employment, in addition to the usual tram wire (a hempen rope, a
wire rope, or a metallic or other rod), along which the load is
transported, of a second or suspension wire or rope to which the tram
wire is connected by tension rods or their equivalent at intervals
between the rigid supports or piers, the object being to diminish or
distribute the sagging or deflection of the tram wire, and thus lessen
the steepness of the gradients over which the load has to be transported.
The combined tram wire, tension rods, suspension wire, and accessories
are, for convenience, designated a "flexible girder."
Another improvement consists in using, when a double line is employed,
stretchers or crossheads to keep the flexible girders nearly parallel to
each other, so that when necessary the load to be transported may be
suspended from or borne by both tram wires jointly or simultaneously,
thus permitting a load of greater weight than that for which each single
tram wire is intended to be carried over the system. One indisputable
claim for confidence in the flexible girder principle is said to be that,
although the peculiar combination of parts constitutes a striking and
valuable novelty, it contains nothing that has not been proved by the
experience of years--nay, generations--to be useful, economic, and
reliable. The usual practice followed in erecting suspension bridges is
applicable in mounting the line, and the carriers, supports, and
carriages may be of any of the usual forms. For the rapid removal of
limited loads wire tramways are in universal favor, and are recognized
not only as very economic and quickly constructed, but also as being in
many cases the only means of transport available except by the adoption
of elaborate and costly engineering works.
It has, it seems, been suggested by some who have examined the
construction of the flexible girder tramway for mineral and produce
traffic that it would be an additional advantage if arrangements were
made for the carriage of small loads--half a dozen or so--of passengers,
the primary intention being to carry the workpeople backward and forward
between comparatively inaccessible mines, works, or plantations and a
neighboring village or town. Compared with every other system where the
line over which the load travels is elevated, the flexible girder tramway
is claimed to possess many advantages--the center of gravity is kept well
down, the liability of the wheels leaving the line is reduced to the
minimum, the gradients are the easiest that can be obtained, there is an
entire absence of jolting and extremely little vibration, and the motion
is altogether smooth and regular; yet it is very questionable whether,
when human life is at stake, any but an ordinary ground line should be
relied upon. A living freight is far more liable than a dead freight to
move during the journey; and as the safety of all overhead lines depends
upon what is scientifically designated "unstable equilibrium," the
flexible girder tramway is not recommendable for passenger lines,
although it can, of course, be fitted for passenger traffic, a suitable
vehicle and ten or a dozen good stout workmen coming well within a
two-ton load, which can be readily carried.
[Illustration: BALL'S FLEXIBLE WIRE TRAMWAY.]
Rope traction or animal traction--practically speaking--is alone
available for wire tramways (that is to say, if the trains are each to be
propelled by its own locomotive--whether steam, springs, or
electricity--the cost of construction and maintenance becomes so serious
that overhead lines, however well designed, are no longer economic); and
experience gained with rope traction in numerous collieries in the North
of England and Lancashire districts--where it is highly appreciated--has
shown that, all circumstances considered, the endless rope is preferable.
The chief objection urged against wire tramways as hitherto constructed
has been that the "sag" of the rope has sometimes caused annoyance to
those using the property passed over, and has always added much to the
cost of traction, owing to the increased power required for moving the
load; this has also resulted in vastly increased wear and tear and the
rapid deterioration and destruction of the wire rope. The flexible girder
system so reduces the "sag" that the maximum economy and durability are
obtained, and the gradients over which the load has to travel can be made
as easy and regular as those upon an ordinary railway. This advantage
will be the more readily appreciated when it is considered that with a
given load on a gradient of 1 in 30 the resistance due to gravity alone
is 200 per cent. greater than on a gradient of 1 in 150, and that the
retardation and wear and tear due to friction, greater curves, and
imperfections increase still more rapidly with increase of gradient, soon
rendering the old sagging wire line practically worthless.
To construct an entire line of flexible girders would be not only
unnecessary, but so costly as to neutralize any advantage which it may
possess, yet for surmounting occasional obstacles the claim made for
it--that it will sometimes permit of a line otherwise impracticable being
cheaply made--seems justified. One can readily imagine a light narrow
gauge line costing L1,000 per mile being laid, for example, between a
mine and the shipping place, and that a swamp, river, or valley would
cost more to bridge over than the whole line besides. If at this obstacle
the trucks or carriages could be lifted bodily, passed along the flexible
girder, and again placed on the line the other side of the obstacle, the
advantage to be derived is obvious; and as the flexible girder is really
little more than a suspension bridge _minus_ the platform, and having but
two suspension wires, the cost and the difficulties should both be very
small.--_Industrial Review_.
* * * * *
BOZERIAN'S REFRIGERANT PUNKAS.
Punkas (also called pankasor tankas) are apparatus that serve for fanning
rooms throughout the entire extent of English India. These devices
consist of a light wooden frame covered with canvas, from the bottom of
which depends a fringe. These frames are suspended from the ceiling in
such a way as to occupy nearly the entire width and length of the room.
To the base of the frame is attached a cord which passes over a wheel,
and which is pulled by a Hindoo domestic. After the frame has been
lifted, a weight fastened to the lower part causes it to fall back again.
The result of the continuous motion of this colossal fan is a coolness
that is highly appreciated in a country where the temperature is at times
incredibly high, and where, without the factitious breeze created by the
punka, living would not be endurable. This breeze prevents perspiration,
or evaporates the same as soon as it is formed. Sometimes it sinks to a
light zephyr; then, if you are reading or writing, you may continue your
work, but in a distracted way, with a moist brow, and with a feeling of
annoyance that soon makes you leave book or pen.
[Illustration: FIG. 1.--TENT OR TABLE FAN OR PUNKA.]
Looking around you, you find the punka immovable. The bahi still holds
the cord that pulls it, but it is because he has tied it to his hand. He
has gently slid to the floor in a squatting posture. He is asleep and you
are burning. A vigorous exclamation brings him to his feet all standing,
and he begins to pull the punka with all his might, and you have a
feeling of ease and coolness. It is like the passage from an attack of
fever to a state of comfort in an intermittent disease. So the punka is
seen everywhere--in the temple and court room and other public places, as
well as in private dwellings. It is one of the first things to astonish
the European upon his arrival in India, and it is not long before he has
to bless the happy invention.
Although, in a country where the temperature generally reaches, and even
often exceeds, 40 deg. C., it is absolutely necessary to obtain by every
means possible a factitious coolness without which the Indies would not
be habitable for Europeans; and although there is no hesitancy in putting
up these punkas everywhere to be maneuvered by bahis, the elevation of
the temperature is not such in France that we are obliged to have
recourse to such processes. But, without being forced thereto by nature,
it is none the less true that we are often the more incommoded by heat in
that we are not accustomed to it, and that in southern France, at certain
hours of the day, such heat becomes absolutely unbearable. We can, it is
true, obtain a little air by moving a fan, but, aside from the fact that
this exercise soon becomes tiresome, it prevents the use of the hand that
is fanning.
[Illustration: FIG 2.--AN APARTMENT FAN.]
The new apparatus which have just been devised by Mr. G. Bozerian permit
of one's fanning himself all day long if he wants to, without any
fatigue, and while he is eating, reading, writing, etc.
In one of these apparatus, designed to be used in the open air (Fig. 1),
we find a table, a tent, and a fan combined; but as each part is
independent, we can have the table and fan without tent, or the fan and
pedals alone without table or tent. Under the tent there is arranged a
frame which pivots freely in apertures formed in the uprights that
support both the tent and table. This frame is connected, through two
levers, with the pedals upon which one's feet rest. The motion of the
pedals is an alternating one like those of sewing machines; but while in
the case of the latter a pressure has to be exerted that soon becomes
very tiresome, the motion in Mr. Bozerian's apparatus is so easy that it
is only necessary to raise the toes of each foot in succession in order
to produce a swing of the fan through the weight alone of the foot that
is pressing. The frame, which when at rest hangs perpendicularly,
describes about a quarter of a circle when the extremity of the foot is
raised about an inch. In consequence of the absence of passive
resistances, motion occurs without any stress, and almost mechanically,
giving air not only to him who is actuating the fan, but also to his
vis-a-vis.
Fig. 2 represents an apartment apparatus designed to be placed in front
of a table or desk, in order that one can fan himself while eating or
writing. Being mounted upon casters, it can be readily moved about from
one place to another. At the extremity of a wooden support, whose height
may be varied at will, there is arranged a flexible fan whose handle is
fixed near a pulley. A small piece of lead forms the counterpoise of the
fan, which is thus completely balanced. Over the pulley runs a cord, each
end of which is attached to a pedal. It will be seen that the alternate
motion of these pedals must cause a rotation of the pulley in one
direction or the other, and that consequently the fan will rise or fall
more or less rapidly, and give a quantity of air that varies according to
the rapidity with which the toes are moved.--_La Nature_.
* * * * *
PUNKAS.
[Footnote: Extract from a lecture recently delivered at Bombay.]
By J. WALLACE, C.E.
The function of a punka is to cause a current of air to pass the human
body so that the animal heat may escape more rapidly. This has nothing to
do with ventilation; for if the punka were used in a closed room, it
would still produce a cooling effect on the skin.
Let us for a moment examine into what takes place in this operation, for
a clear idea of the cause of our sensations of heat is absolutely
necessary to enable us to go directly to the simplest and best form of
remedy. The heat we feel, and which sometimes renders us uncomfortable,
is produced _within us_ by the slow combustion of the food we eat.
This heat continues to escape from the whole surface of the body during
the whole lifetime, and if anything occurs to arrest it to any great
extent, the result is fatal.
In cold weather, and especially when there is much wind, the animal heat
escapes very rapidly from the body, and extra clothing is used, not for
any heat it imparts, but simply because it interrupts the escape of the
heat, and thus maintains the temperature of the skin--that part of us
which is most sensible of change of temperature. It is a wonderful fact
that the heat of the interior of the body varies very little in a healthy
man between India and Greenland.
The skin may bear a good many degrees of change of temperature with
impunity, but the blood will only suffer a very small variation from the
normal temperature of 98-4/10 deg. Fahrenheit without serious consequences.
Well, to keep the skin at an agreeable temperature in India we generally
wear a minimum of clothing, and when there is no breeze, we try to
produce one with the punka.
The escape of animal heat from the body forms a subject which is much
more complicated, and much more important, than the one we have met to
consider, but it is impossible within the limits of our time to refer to
it, except in the measure that is strictly necessary to elucidate the
principles that should control the construction of the punka.
It has often been said that every engineer on his arrival in India sets
about improving this useful apparatus; but if we may judge from the
endless variety of forms which may be seen in shops and offices, in
public and in private buildings, no general principle of construction has
been recognized, and the punka, as we see it, seems to depend, for its
form, more upon the taste of the workman who makes it than on anything
else.
We shall begin by directing our attention to the suspended punka, which
is usually hung from the ceiling, and put in movement by a cord. The
object of this class of punka is to produce a downward current of air by
swinging to and fro, and the best punka is the one which throws downward
the greatest quantity of air with the smallest applied force.
The swinging punka is one of the simplest forms of mechanism; it can be
fitted up with the most primitive materials, and however badly made, it
will always have _some_ effect. This fact has its good and its bad
aspects; it brings a certain comfort within the reach of all, but it
removes a great part of that _necessity_ which, as we all know, is the
mother of invention.
There are some very important natural laws which are illustrated in the
punka. The first is that which governs the movement of the pendulum. The
number of swings it makes per minute depends on the length of the
suspending cords; a pendulum three feet long will swing 621/2 times per
minute, and a pendulum six feet long will swing 441/4 times per minute.
Whether the swings are long ones or short ones, the number per minute is
still the same. You cannot, therefore, alter the natural rate of movement
of a punka unless you pull it at both sides.
The next law is that which determines that the angles of incidence and of
reflection are equal. This in simple language means that it is useless to
expect a good downward current of air from a slow moving and heavy punka,
with long suspending cords which keep it nearly always in a vertical
position to its plane of movement. Striking the air squarely as it does
in its forward and backward movement, it throws almost as much air upward
as downward, and of course all the air that is propelled in any other
than a downward direction represents just so much power wasted.
One more law, and then we may proceed to demonstration.
As the air weighs 0.072 lb. per cubic foot at 82 deg. Fahrenheit, and as a
considerable quantity of air is put in motion, the power required to
drive a punka depends upon the quantity of air it puts in motion in a
given time.
The _useful effect_ is a separate matter; it depends on the amount of air
thrown in a downward direction.
To summarize; all punkas of the same size or surface, and going at the
same speed, require the same amount of pulling. The best one is that
which will throw down more air than any other of the same size.
To obtain the greatest result from the power expended in driving it, the
punka should be placed as near as possible to the person to be cooled,
as the loss of effect, due to distance, increases not in direct ratio,
but in proportion to the square of the distance between punka and person.
If at two feet of distance he receives one eighth of the total effect, he
will at four feet of distance obtain only one thirty-second part.
In practice, the punka should just clear his head when standing, and the
weighting of the curtain should be of some yielding material, so as not
to damage any person who might stand in its course.
We shall now proceed to examine several forms of punka, all made to the
same size, and, for purposes of comparison, we shall drive them all at
the same speed. And in order that their effects may be visible to you, I
have prepared an indicator which resembles more than anything else the
keyboard of a piano. It consists of a series of balanced levers with
blades or keys attached, forming a keyboard four feet long. The levers,
each three feet long, are delicately hung on fine brass centers, and each
lever is counterbalanced by a weight hung in a vessel of water, which
acts as a hydraulic brake, and checks any spasmodic movement in the
apparatus.
On the end of each blade is fixed a disk of white Bristol board four
inches in diameter, forming a row which faces the audience.
This apparatus is so sensitive that a slight change in the humidity of
the atmosphere is sufficient to throw it out of balance.
The power required to drive a punka is nearly all due to the resistance
of the air; that part due to the force of gravity, and the friction of
the suspending joints, is scarcely worth counting. We may readily observe
the effect of the resistance of the air by swinging two pendulums of
equal length and having each a large cardboard disk attached. One of the
disks shall present its edge to the line of movement, and the other its
face.
_Exp. 1._--They are now swinging, and being both of the same gravity
length, they should swing together and for an equal length of time. This
they would do in a vacuum, but you have already observed that one of them
is lagging, and will evidently soon come to a standstill. It is the one
_facing_ the air.
If punkas were pulled from both sides, they might be made very much
lighter than they are at present, but for the sake of simplicity a single
pull is preferred. They must, therefore, be made of such a weight that
they will swing nearly as far on the opposite side as they are pulled on
the near side; any greater weight is useless and only serves to wear out
the suspending cords, which, by the way, are nearly always too numerous
and too thick for their purpose.
_Exp. 2._--Here is a panel punka which we shall try to use without the
customary swing bar. It is of calico stretched on a light wooden frame,
and you will be able to judge if it swings equally on each side of the
post which supports it. The irregularity of its movement shows that it is
too light, so we shall add, by way of swing bar, a bar of round iron one
and a quarter inch thick.
_Exp. 3._--It is now swinging regularly, and experiments have already
proved that the swing bar should not be lighter than this one, which
weighs four and a sixth lb. per foot of length. Iron is the best material
for this purpose, as it offers the smallest surface to the resistance of
the air. The length of the suspending cords is usually a matter of
accident in the construction of a punka, but a little attention to the
subject will soon convince us that it is one of the most important
considerations.
The limit of movement of a punka is to be found in the man who pulls it.
Twenty-four pulls a minute of a length of 36 inches give in practice a
speed of 168 linear feet to the punka curtain. This speed is found to
produce a current sufficiently rapid for practical purposes, and
twenty-four pulls or beats per minute correspond to a length of
suspending cord of fifty inches.
* * * * *
HOW TO MAKE A KITE WITHOUT A TAIL.
The following is the method of making a kite without a tail: All the
calculations necessary in order to obtain the different proportions are
based upon the length of the stick, A'A, employed. Such length being
found, we divide it by ten, and thus obtain what is called the unit of
length. With such unit it is very easy to obtain all the proportions. The
bow, K'K, consists of two pieces of osier each 51/2 units in length, that
form, through their union, a total length of 7 units.
[Illustration: KITE WITHOUT A TAIL.]
After the bow has been constructed according to these measurements, it
only remains to fix it to the stick in such a way that it shall be two
units distant from the upper end of the stick. The balance, CC', whose
accuracy contributes much to the stability of the whole in the air,
consists of a string fixed at one end to the junction, D, of the bow and
stick, and at the other to the stick itself at a distance of three units
from the lower extremity. Next, a cord, B, is passed around the frame,
and the whole is covered with thin paper.
Before raising the kite, the string, which hangs from K', is made fast at
K in such a way as to cause the bow to curve backward. This curvature is
increased or diminished according to the force of the wind.
Nothing remains to be done but to attach the cord to the balance, and
raise the kite.--_La Nature_.
* * * * *
APPARATUS FOR DRYING FLOUR.
The accompanying drawing represents a simple but effective apparatus for
drying flour and ascertaining the quantity of water contained therein. It
consists of four pieces, the whole being made of block tin. A is a simple
saucepan for containing the water. B is the lid, which only partially
covers the top of the pan, to which it is fixed by two slots, a hole
being left in the middle for the placing of the vessel which contains the
flour to be operated upon, and is dropped in in the same way as the pan
containing the glue is let into an ordinary glue pot. C is the spout,
which serves as an outlet for the steam arising from the boiling water. D
is the vessel in which the flour is placed to be experimented upon; and
EE are the funnels of the lid which covers the said vessel, and which
serve as escapes for the steam arising from the moisture contained in the
flour.
[Illustration: APPARATUS FOR DRYING FLOUR]
_Directions for use_.--Partially fill the pan with water and allow it to
boil. Place a given quantity of flour in the inner vessel, D, taking care
first to weigh it. Subject it to the action of the boiling water until it
is perfectly dry, which will be indicated by the steam ceasing to issue
from the funnels. Then weigh again, and the difference in the weight will
represent the quantity of moisture contained in it, dried at a
temperature of 212 degrees Fahr., that of boiling water.--_The Miller_.
* * * * *
APPARATUS FOR MANUFACTURING BOUQUETS.
For some years past, the sale of flowers has been gradually increasing.
Into the larger cities, such as Paris for example, they are introduced by
the car load, and along about the first of January the consumption of
them is extraordinary. All choice flowers are now being cultivated by
improved methods that assure of an abundant production of them. What
twenty years ago would have appeared to be an antiquated mechanism, viz.,
an apparatus for making bouquets, has now become a device of prime
necessity by reason of the exigencies of an excessive demand.
Mr. Myard, a gardener of Chalon-sur-Saone, and vice-president of the
horticultural society of that city, has devised a curious apparatus,
which we represent herewith from a photograph.
This bouquet machine, which the inventor styles a _bouquetiere_, consists
of a stationary rod (shown to the right of the figure), upon which slides
a spool wound with twine, and the lower part of which is provided with
three springs for keeping the twine taut. A horizontal arm at the top
supports a guide or pattern whose curve is to be followed, on placing the
flowers in position. This arm is removed or turned aside after the
binding screw has been loosened, in order that the rod to the left that
carries the bouquet may be taken out. A guide, formed of a steel ribbon,
is fixed to the arm and to its movable rod by means of binding screws,
which permit of its being readily elongated. This central rod can be
raised or lowered at will, and, owing to these combinations, every
desired form of bouquet may be obtained.
[Illustration: APPARATUS FOR MAKING BOUQUETS.]
The rod to the left is provided with a steel pivot, and contains several
apertures, into which a pin enters, thus rendering it easy to begin
bouquets at different heights.
The bouquet is mounted upon the rod to the left, as shown in the figure.
The pin passes through the rod and enters a loop formed at the extremity
of the twine, and thus serves as a point of support, and prevents the
bouquet from falling, no matter what its weight is. When the pin is
removed in order that the bouquet may be taken out, the loop escapes.
At the lower part of the rod upon which the bouquet is mounted, there is
a collar with three branches, by means of which a rotary motion is given
to the flowers through the aid of the hand. The twine used for tying is
thus wound around the stems. When the apparatus is in motion, the twine
unwinds from the spool, and winds around the rod that carries the
flowers, and twists about and holds every stem.
An experienced operator can work very rapidly with this little apparatus,
which has been constructed with much care and ingenuity, and which enters
into a series of special mechanisms that is always of interest to know
about.
The manufacturer was advised to construct his apparatus so that it could
be run by foot power, but, after some trials, it was found that the
addition of a pedal and the mechanism that it necessitates was absolutely
superfluous, the apparatus working very well such as it is.--_La Nature_.
* * * * *
[Continued from SUPPLEMENT, No. 567, page 9057.]
RADII OF CURVATURE GEOMETRICALLY DETERMINED.
By Prof. C.W. MACCORD, Sc.D.
NO. VII.--PATH OF A POINT ON A CONNECTING ROD.
The motion of the connecting rod of a reciprocating steam engine is very
clearly understood from the simple statement that one end travels in a
circle and the other in a right line. From this statement it is also
readily inferred that the path of any point between the centers of the
crank and crosshead pins will be neither circular nor straight, but an
elongated curve. This inference is so far correct, but the very common
impression that the middle point of the rod always describes an ellipse
is quite erroneous. The variation from that curve, while not conspicuous
in all cases, is nevertheless quite sufficient to prevent the use of this
movement for an elliptograph. To this there is, abstractly, one
exception. Referring to Fig. 22 in the preceding article, it will be seen
that if the crank OH and the connecting HE are of equal length, any point
on the latter or on its prolongation, except E, H, and F, will describe
an exact ellipse. But the proportions are here so different from anything
used in steam engines (the stroke being four times the length of the
crank), that this particular arrangement can hardly be considered as what
is ordinarily understood by a "crank and connecting rod movement," such
as is shown in Fig. 23.
The length DE of the curve traced by the point P will evidently be equal
to A'B', the stroke of the engine, and that again to AB, the throw of the
crank. The highest position of P will be that shown in the figure,
determined by placing the crank vertically, as OC. At that instant the
motions of C and C' are horizontal, and being inclined to CC' they must
be equal. In other words, the motion is one of translation, and the
radius of curvature at P is infinite.
To find the center of curvature at D, assume the crank pin A to have a
velocity A_a_. Then, since the rod is at that instant turning about the
farther end A', we will have D_d_ for the motion of D. The instantaneous
axis of the connecting rod is found by drawing perpendiculars to the
directions of the simultaneous motions of its two ends, and it therefore
falls at A', in the present position. But the perpendicular to the motion
of the crank pin is the line of the crank itself, and consequently is
revolving about O with an angular velocity represented by AO_a_. The
motion of A' is in the direction A'B', but its velocity at the instant is
zero. Hence, drawing a vertical line at A', limited by the prolongation
of _a_O, we have A'_a_' for the motion of the instantaneous axis.
Therefore, by drawing _a_'_d_, cutting the normal at _x_, we determine
D_x_, the radius of curvature.
Placing the crank in the opposite position OB, we find by a construction
precisely similar to the above, the radius of curvature E_z_ at the other
extremity of the axis of the curve. It will at once be seen that E_z_ is
less than D_x_, and that since the normal at P is vertical and infinite,
the evolute of DPE will consist of two branches _x_N, _z_M, to which the
vertical normal PL is a common asymptote. These two branches will not be
similar, nor is the curve itself symmetrical with respect to PL or to any
transverse line; all of which peculiarities characterize it as something
quite different from the ellipse.
[Illustration: FIG. 23.]
[Illustration: FIG. 24.]
[Illustration: FIG. 25.]
Moreover, in Fig. 22, the locus of the instantaneous axis of the trammel
bar (of which the part EH corresponds to the connecting rod, when a crank
OH is added to the elliptograph there discussed) was found to be a
circle. But in the present case this locus is very different. Beginning
at A', the instantaneous axis moves downward and to the right, as the
crank travels from A in the direction of the arrow, until it becomes
vertical, when the axis will be found upon C'R, at an infinite distance
below AB', the locus for this quarter of the revolution being a curve
A'G, to which C'R is an asymptote. After the crank pin passes C, the axis
will be found above AB' and to the right of C'R, moving in a curve HB',
which is the locus for the second quadrant. Since the path of P is
symmetrical with respect to DE, the completion of the revolution will
result in the formation of two other curves, continuous and symmetrical
with those above described, the whole appearing as in Fig. 24, the
vertical line through C' being a common asymptote.
In order to find the radius of curvature at any point on the generated
curve, it is necessary to find not only the location of the instantaneous
axis, but its motion. This is done as shown in Fig. 25. P being the given
point, CD is the corresponding position of the connecting rod, OC that of
the crank. Draw through D a perpendicular to OD, produce OC to cut it in
E, the instantaneous axis. Assume C A perpendicular to OC, as the motion
of the crank. Then the point E in OC produced will have the motion EF
perpendicular to OE, of a magnitude determined by producing OA to cut
this perpendicular in F. But since the _intersection_ E of the crank
produced is to be with a vertical line through the other end of the rod,
the instantaneous axis has a motion which, so far as it depends upon the
movement of C only, is in the direction DE. Therefore EF is a component,
whose resultant EG is found by drawing FG perpendicular to EF. Now D is
moving to the left with a velocity which may be determined either by
drawing through A a perpendicular to CD, and through C a horizontal line
to cut this perpendicular in H, or by making the angle DEI equal to the
angle CEA, giving on DO the distance DI, equal to CH. Make EK = DI or
CH, complete the rectangle KEGL, and its diagonal ES is, finally, the
motion of the instantaneous axis.
EP is the normal, and the actual motion of P is PM, perpendicular to EP,
the angle PEM being made equal to CEA. Find now the component EN of the
motion ES, which is perpendicular to EP. Draw NM and produce it to cut EP
produced in R the center of curvature at P.
This point evidently lies upon the branch _z_M of the evolute in Fig. 23.
The process of finding one upon the other branch _x_N is shown in the
lower part of the diagram, Fig. 25. The operations being exactly like
those above described, will be readily traced by the reader without
further explanation.
* * * * *
AUTOMATIC COMMUTATOR FOR INCANDESCENT LAMPS.
Incandescent electric lighting, already pushed to such a degree of
perfection in the details of construction and installation, continually
finds new exigencies that have to be satisfied. As it is more and more
firmly established, it has to provide for all the comforts of existence
by simple solutions of problems of the smaller class.
Take for example this case: Suppose a room, such as an office, lighted by
a single lamp. The filament breaks; the room becomes dark. The bell push
is not always within reach of the arm, and it is by haphazard that one
has to wander around in the dark. This is certainly an unpleasant
situation. The comfort we seek for in our houses is far from being
provided.
M. Clerc, the well known inventor of the sun lamp, has tried to overcome
troubles of this sort, and has attained a simple, elegant, and at the
same time cheap solution. The cut shows the arrangement. The apparatus is
connected at the points, BB', with the lighting circuit. The current
entering by the terminal, B', passes through the coils of a bobbin, S,
before reaching the points of attachment, a and b, of the lamp, L, the
normally working one. Thence the circuit runs to B. Within the coil, S,
is a small hollow cylinder, T, of thin sheet iron, which is raised
parallel with the axis of the bobbin during the passage of the current
through the latter. At its base the cylinder is prolonged into two little
rods, h and h', which plunge into two mercury cups, G and G'. The cut
shows that one of the cups, G', is connected to the terminal, B', and the
other, G, to the terminal, a', of the other lamp, L'. An inspection of
the cut shows just what ensues when an accident happens to the first lamp
while burning. The first circuit being broken at ab, the magnetizing
action of the current in the bobbin ceases, the cylinder, T, descends,
and the rods, h and h', dip into the mercury. It follows that the
current, always starting from the terminal, B', will by means of the
cups, G and G', pass through the lamp, L', to go by the original return
wire to B.
[Illustration]
The substitution of the lamp, L, for L' is almost instantaneous. It can
scarcely be perceived. It goes without saying that such an arrangement of
automatic commutation is applicable to lamps with two or more filaments
of which only one is to be lighted at a time. The apparatus costs little,
and can be made as ornamental as desired. No exaggeration is indulged in
if we pronounce it simple and ingenious. It may be used in a great
variety of eases. The diameter of the wire is 55/100 (22 mm.), its length
eighteen meters (60 feet), its resistance one ohm; 3/4 ampere is needed to
work it, and less than a watt is absorbed by it.--_Electricite_.
* * * * *
DEFINITIONS AND DESIGNATIONS IN ELECTROTECHNICS.
We may discourse for some time to come upon the uniformity of electric
language, for universal agreement is far from being established. An
important step toward the unity of this language was taken in 1881 by the
congress of Paris, which rendered the use of the C.G.S. system definitive
and universal. This labor was completed in 1884 by the meeting of a new
congress at Paris, at which a definition of the C.G.S. and practical
units was distinctly decided upon. That the unit of light defined by the
congress has not rapidly come into favor is due to the fact that its
practical realization is not within everybody's reach.
The work of unification should not come to a standstill on so good a
road. How many times in scientific works or in practical applications do
we find the same physical magnitude designated by different names, or
even the use of the same expression to designate entirely different
things!
The result is an increase of difficulties and confusions, not only for
persons not thoroughly initiated into these notions, but also for adepts,
even, in this new branch of the engineer's art. The effects of such
confusion make themselves still further felt in the reading of foreign
publications. Thus, for example, in Germany that part of a dynamo
electric machine that is called in France the _induit_ (armature) is
sometimes styled _anker_, and more rarely _armatur_. The _north pole_ of
a freely suspended magnetized needle is the one that points toward the
geographical north of the earth. In France, and by some English authors,
this pole is called the _south_ one. Among electricians of the same
country, what by one is called _electro-motive force_ is by another
styled _difference of potential_, by a third _tension_, and even
_difference of tension_.
Our confrere Ruhlmann, of the _Elektrotechnische Zeitschrift_, gives a
still more remarkable example yet of such confusion. The word
_polarization_, borrowed from optics, where it has an unequivocal sense,
serves likewise to designate the development of the counter
electro-motive force of galvanic elements, and also that essentially
different condition of badly conducting substances that is brought about
by the simultaneous influence of quantities of opposite electricity.
In Germany, the word _induction_, coupled with the word _wire_, for
example, according to the formation of compound words in that language,
may also have a double meaning, and it is by the sense alone of the
phrase that we learn whether we have to do with an induced wire or an
inducting one. The examples might be multiplied.
At its session of November 5, 1884, the International Society of
Electricians, upon a motion of Mr. Hospitalier, who had made a
communication upon this question, appointed a committee to study it and
report upon it. The English Society of Electricians likewise took the
subject into consideration, and one of its most active and distinguished
members, Mr. Jamieson, presented the result of his labors at the May
session of the society in 1885.
A discussion arose in which the committee of the International Society of
Electricians was invited to take part. The committee was represented by
its secretary, Mr. Hospitalier, who expressed himself in about these
words: "The committee on electric notations presided over by Mr. Blauvelt
has finished a part of its task, that relative to abbreviations,
notations, and symbols. It will soon take up the second part, which
relates to definitions and agreements." He broadly outlined the
committee's ideas as follows:
In all physical magnitudes that are made use of, we have: (1) the
physical magnitude itself, aside from the units that serve to measure it;
(2) the C.G.S. unit that serves to measure such grandeur (granted the
adoption of the C.G.S. system); (3) practical units, which, in general,
have a special name for each kind of magnitude, and are a decimal
multiple or sub-multiple of the C.G.S. unit, except for time and angles;
(4) finally, decimal multiples and sub-multiples of these practical
units, that are in current use.
The committee likewise decided always to adopt a large capital to
designate the physical magnitude; a small capital to designate the C.G.S.
unit, when it has a special name; a "lower case" letter for the
abbreviation of each practical unit; and prefixes, always the same, for
the decimal multiples and sub-multiples of the practical units.
Thus, for example, work would be indicated by the letter W (initial of
the word); the C.G.S. unit is the _erg_, which would be written without
abbreviation, on account of its being short; and the practical units
would be the kilogrammeter (_kgm_), the grammeter (_gm_), etc. The
multiples would be the _meg-erg_, the tonne-meter (_t-m_), etc.
Mr. Jamieson's propositions have been in great part approved. Some
criticisms, however, were made during the course of the discussion, and
it is for this reason that the scheme still remains open to improvements.
The proposed symbols are as follows:
A.--PRACTICAL ELECTRIC UNITS.
Total resistance of a circuit. R
Internal resistance of a source of current. r_{1}
Resistance of the separate parts of a current. _r__{1}, _r__{2}, etc.
Specific resistance. [rho]
1 ohm. [omega]
1 megohm. [Omega]
Intensity of a current. C
Magnitude of 1 ampere. A
1 milliampere. [alpha]
Electro-motive force. E
Magnitude of 1 volt. _v_
Capacity. K
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