Scientific American Supplement, No. 595, May 28, 1887
by
Various
Part 2 out of 3
Constant of specific induction. [sigma]
1 farad. [Phi]
1 microfarad. [phi]
Quantity of electricity. Q
1 coulomb. C
Electric work (volt coulomb). _v_C
Electric effect (volt ampere, watt in one second). W
Horse power. HP
B.--MAGNETISM.
Pole of magnet pointing toward the north. N
The opposite pole. S
Force of a pole, quantity of magnetism. _m_
Distance of the poles of a magnet. _l_
Magnetic moment. M = _m.l_
Intensity of magnetization. J
Intensity of the horizontal component of terrestrial
magnetism. H
C.--ELECTRIC MEASUREMENTS.
Galvanometer and its resistance. G
Resistance of the shunt of a galvanometer. _s_
Battery and its internal resistance. B
For dynamo machines, the following designations
are proposed:
The machine itself. D
Positive terminal. +T
Negative terminal. -T
Magnet forming the field. FM
Current indicator (amperemeter). AM
Tension indicator (voltameter). MV
Electro-magnet. EM
Luminous intensity of a lamp, in candles. _c.p_.
Resistance of the armature. R_{a}
Resistance of the magnet forming the field. R_{m}
Resistance of the external circuit. R_{o}
Intensity in the armature. C_{a}
Intensity in the coils of the magnet. C_{m}
Intensity in the external circuit. C_{e}
Coefficient of self-induction. L_{s}
Coefficient of mutual induction. L_{m}
A primary battery would be represented as in Fig. 1, and a battery of
accumulators as in Fig. 2.
[Illustration: FIG. 1.]
[Illustration: FIG. 2.]
In order to designate incandescent lamps, circles would be used, and
stars for arc lamps. A system of incandescent lamps arranged in multiple
arc would be represented as in Fig. 3.
[Illustration: FIG. 3.]
Fig. 4 and the formula
R = B + Gs/(G + s) + r
would serve for the total resistance, R, of an electric circuit, upon
giving the letters the significations adopted.
[Illustration: FIG. 4.]
Such is, in brief, the present state of the question. The scientific
bodies that have taken hold of it have not as yet furnished a fully
co-ordinated work on the subject. Let us hope, however, that we shall not
have to wait long. The question is of as much interest to scientific men
as to practical ones.
A collection of identical symbols would have the advantage of permitting
us to abridge explanations in regard to the signification of terms used
in mathematical formulas. A simple examination of a formula would suffice
to teach us its contents without the aid of tiresome explanatory matter.
But in order that the language shall be precise, it will be necessary for
the words always to represent precise ideas that are universally
accepted, and for their sense not to depend upon the manner of
understanding the idea according to their arrangement in the phrase.
Nothing can be more desirable than that the societies of electricians of
all countries shall continue the study of these questions with the desire
of coming to a common understanding through a mutual sacrifice of certain
preferences and habitudes.--_E. Dieudonne, in La Lumiere Electrique_.
* * * * *
IMPROVED MICROSCOPICAL SETTLING TUBE.
By F. VANDERPOEL, of Newark, New Jersey.
In the February number of this _Journal_ the writer described a new
settling tube for urinary deposits which possessed several advantages
over the old method with conical test-glass and pipette. For several
reasons, however, the article was not illustrated, and it is for the
purpose of elucidation by means of illustration, as well as to bring
before the readers of the _Journal_ two new and improved forms of the
tube, that space in these columns is again sought. The first two of the
figures, 1 and 2, represent the tube as originally devised; 1 denoting
the tube with movable cap secured to it by means of a rubber band, and 2
the tube with a ground glass cap and stop cock. The first departure from
these forms is shown at 3, and consists of a conical tube, as before, but
provided with a perforated stopper, the side opening in which
communicates with a side tube. The perforation in the stopper, which is
easily made by a glass blower, thus allows the overflow, when the stopper
is inserted into the full tube, to pass into the side tube. The stopper
is then turned so as to cut off the urine in the latter from that in the
large tube, and the latter is thus made tight. After allowing it to
remain at rest long enough to permit subsidence of all that will settle,
the stopper is gently turned and a drop taken off the lower end upon a
slide, to be examined at leisure with the microscope. The cap, ground and
fitted upon the lower end, is put there as a precautionary measure, as
will be seen farther on.
[Illustration: VANDERPOEL'S SETTLING TUBES.]
The tube shown at 4 is, we think, an improvement upon all of the
foregoing, for upon it there is no side tube to break off, and everything
is comprised in a small space. As will be seen by referring to the
figure, there is a slight enlargement in the ground portion of the
stopper end of the tube, this protuberance coming down about one-half the
length of the stopper, which is solid and ground to fit perfectly. The
lower half, however, is provided with a small longitudinal slit or
groove, the lower end of which communicates with the interior of the
tube, while the upper end just reaches the enlargement in the side of the
latter. Thus in one position of the stopper there is a communication
between the tube and the outer air, while in all other positions the tube
is quite shut. In all these tubes care must be taken to fill them
_completely_ with the urine, and to allow no bubbles of air to remain
therein.
The first of these settling tubes was made without the ground cap on the
lower end, the latter being inserted into a small test tube for safety.
At the suggestion of Mr. J.L. Smith the test tube was made a part of the
apparatus by fitting it (by grinding) upon the conical end, and in its
present form it serves to protect the latter from dust and to prevent
evaporation of the urine (or other liquid), and consequent deposition of
salts, if, for any reason, the user should allow the tube to remain
suspended for several days.
These tubes will be found very useful for collecting and concentrating
into a small bulk the sediment contained in any liquid, whether it be
composed of urinary deposits, diatoms in process of being cleaned, or any
thing of like nature; and, as the parts are all of glass, the strongest
acids may be used, excepting, of course, hydrofluoric acid, without harm
to the tubes.--_American Microscopical Journal_.
* * * * *
[Continued from SUPPLEMENT, No. 594, page 9491.]
CLIMATE IN ITS RELATION TO HEALTH. By G.V. POORE, M.D.
[Footnote: Three lectures before the Society of Arts, London. From the
Journal of the Society.]
LECTURE III. DISEASES CAUSED BY FLOATING MATTER IN THE AIR.
The information which modern methods of research have given us with
regard to the floating matter in the air is of an importance which cannot
be overestimated.
That the air is full of organic particles capable of life and growth is
now a matter of absolute certainty. It has long been a matter of
speculation, but there is a great difference between a fact and a
speculation. An eminent historian has recently deprecated the distinction
which is conventionally drawn between science and knowledge, but,
nevertheless, such a distinction is useful, and will continue to be
drawn. A man's head may be filled with various things. His inclination
may lead him, for example, to study archaic myths in the various dialects
which first gave them birth; he may have a fancy for committing to memory
the writings of authors on astrology, or the speculations of ancient
philosophers, from Aristotle and Lucretius downward. Such a one may have
a just claim to be considered a man of learning, and far be it from me to
despise the branches of knowledge toward which his mind has a natural
bent. But in so far as his knowledge is a knowledge of fancies rather
than facts, it has no claim to be called science.
Fancies, however beautiful, cannot form a solid basis for action or
conduct, whereas a scientific fact does. It is all very well to suppose
that such and such things may be, but mere possibilities, or even
probabilities, do not breed a living faith. They often foster schism, and
give rise to disunited or opposed action on the part of those who think
that such and such things may not be.
When, however, a fancy or a speculation becomes a fact which is capable
of demonstration, its universal acceptance is only a matter of time, and
the man who neglects such facts in regulating his actions or conduct is
rightly regarded as insane all the world over.
The influence of micro-organisms on disease is emerging more and more,
day by day, from the regions of uncertainty, and what once were the
speculations of the few are now the accepted facts of the majority.
Miquel's experiments show very clearly that the number of microbes in the
air corresponds with tolerable closeness to the density of population.
From the Alpine solitudes of the Bernese Oberland to the crowded ward of
a Parisian hospital, we have a constantly ascending ratio of microbes in
the air, from zero to 28,000 per cubic meter. Their complete absence on
the Alps is mainly due to the absence of productive foci. Organic matter
capable of nourishing microbes is rare, and the dryness and cold prevent
any manifestation of vitality or increase. Whence come the large number
of microbes in the crowded places and in hospitals?
Every individual, even in health, is a productive focus for microbes;
they are found in the breath, and flourish luxuriantly in the mouth of
those especially who are negligent in the use of the tooth brush. When we
speak of "flourishing luxuriantly," what do we mean? Simply that these
microbes, under favorable circumstances, increase by simple division, and
that one becomes about 16,000,000 in twenty-four hours.
The breath, even of healthy persons, contains ammonia and organic matter
which we can smell. When the moisture of the breath is condensed and
collected, it will putrefy. Every drop of condensed moisture that forms
on the walls of a crowded room is potentially a productive focus for
microbes. Every deposit of dirt on persons, clothing, or furniture is
also a productive focus, and production is fostered in close apartments
by the warmth and moisture of the place. In hospitals productive foci are
more numerous than in ordinary dwellings.
If microbes are present in the breath of ordinary individuals, what can
we expect in the breath of those whose lungs are rotten with tubercular
disease? Then we have the collections of expectorated matter and of other
organic secretions, which all serve as productive foci. Every wound and
sore, when antiseptic precautions are not used, becomes a most active and
dangerous focus, and every patient suffering from an infective disease is
probably a focus for the production of infective particles. When we
consider, also, that hospital wards are occupied day and night, and
continuously for weeks, it is not to be wondered at that microbes are
abundant therein.
I want especially to dwell upon the fact that foci, and probably
productive foci, may exist outside the body. It is highly probable,
judging from the results of experiments, that every collection of
putrescible matter is potentially a productive focus of microbes. The
thought, of a pit or sewer filled with excremental matters mixed with
water, seething and bubbling in its dark warm atmosphere, and
communicating directly (with or without the intervention of that
treacherous machine called a trap) with a house, is enough to make one
shudder, and the long bills of mortality already chargeable to this
arrangement tell us that if we shudder we do not do so without cause. As
an instance of the way in which dangers may work in unsuspected ways, I
may mention the fact that Emmerich, in examining the soil beneath a ward
of a hospital at Amberg, discovered therein the peculiar bacillus which
causes pneumonia, and which had probably been the cause of an outbreak of
pneumonia that had occurred in that very ward.
The importance of "Dutch cleanliness" in our houses, and the abolition of
all collections of putrescible matter in and around our houses, is
abundantly evident.
It will not be without profit to examine some well-known facts, by the
aids of the additional light which has been thrown upon them by the study
of the microbes which are in the media around us.
There is no better known cause of a high death rate than overcrowding.
Overcrowding increases the death rate from infectious diseases,
especially such as whooping cough, measles, scarlet fever, diphtheria,
small-pox, and typhus. The infection of all these diseases is
communicable through the air, and where there is overcrowding, the chance
of being infected by infective particles, given off by the breath or
skin, is of course very great. Where there is overcrowding, the
collections of putrescible filth are multiplied, and with them probably
the productive foci of infective particles. Tubercular disease, common
sore throat, chicken-pox, and mumps, are also among the diseases which
are increased by overcrowding.
To come to details which are more specific, let us consider the case of
some diseases which are definitely caused by floating matter in the air.
First, let us take one which is apparently attributable to pollen.
HAY FEVER.
Among diseases which are undoubtedly caused by floating matter in the air
must be reckoned the well-known malady "hay fever," which is a veritable
scourge during the summer months to a certain percentage of persons, who
have, probably, a peculiarly sensitive organization to begin with, and
are, in a scientific sense, "irritable."
This disease has been most thoroughly and laboriously investigated by Mr.
Charles Blackley, of Manchester, who, being himself a martyr to hay
fever, spent ten years in investigating the subject, and published the
result in 1873, in a small work entitled "Experimental Researches on the
Causes and Nature of _Catarrhus aestivus_ (hay fever or hay asthma)."
Mr. Blackley had little difficulty in determining that the cause of his
trouble was the pollen of grasses and flowers, and his investigations
showed that the pollen of some plants was far more irritating than the
pollen of others. The pollen of rye, for example, produced very severe
symptoms of catarrh and asthma, when inhaled by the nose or mouth. Mr.
Blackley came to the conclusion that the action of the pollen was partly
chemical and partly mechanical, and that the full effect was not produced
until the outer envelope burst and allowed of the escape of the granular
contents.
Having satisfied himself that pollen was capable of producing all the
symptoms of hay fever, Mr. Blackley next sought to determine, by a series
of experiments, the quantity of pollen found floating in the atmosphere
during the prevalence of hay fever, and its relation to the intensity of
the symptoms. The amount of pollen was determined by exposing slips of
glass, each having an area of a square centimeter, and coated with a
sticky mixture of glycerine, water, proof spirit, and a little carbolic
acid. Mr. Blackley gives two tables, showing the average number of pollen
grains collected in twenty-four hours on one square of glass, between May
28 and August 21, in both a rural and an urban position. The maximum both
in town and country was reached on June 28, when in the town 105 pollen
grains were deposited, and in the country 880 grains. The number of
grains deposited was found to vary much, falling almost to zero during
heavy rain and rising to a maximum if the rain were followed by bright
sunshine. Mr. Blackley found that the severity of his own symptoms
closely corresponded to the number of pollen grains deposited on his
glasses. Mr. Blackley devised some very ingenious experiments to
determine the number of grains floating in the air at different
altitudes. The experiments were conducted by means of a kite, to which
the slips of glass were attached, fixed in an ingenious apparatus, by
means of which the surface of the glass was kept covered until a
considerable altitude had been reached. Mr. Blackley's first experiment
gave as a result that 104 pollen grains were deposited in the glass
attached to the kite, while only 10 were deposited on a glass near the
ground. This experiment was repeated. Again and again, and always with
the same result, there was more pollen in the upper strata of the air
than in the lower.
A very interesting experiment was performed at Filey, in June, 1870. A
breeze was blowing from the sea, and had been blowing for 12 or 15
hours. Mr. Blackley flew his kite to an elevation of 1,000 feet. The
glass attached to the kite was exposed for three hours, and on it there
were 80 grains of pollen, whereas a similar glass, exposed at the margin
of the water, showed no pollen nor any organic form. Whence came this
pollen collected on the upper glass? Probably from Holland or Denmark.
Possibly from some point nearer the center of Europe.
POTATO DISEASE.
A study of the terrible disease which so often attacks the potato crop in
this country will serve, I think, to bring forcibly before you certain
untoward conditions which may be called climatic, and which are
attributable to fungoid spores in the air.
With the potato disease you are all, probably, more or less practically
acquainted. When summer is at its height, and when the gardeners and
farmers are all looking anxiously to the progress of their crops, how
often have we heard the congratulatory remark of "How well and strong
those potatoes look!" Such a remark is most common at the end of July or
the beginning of August, when the green part, or haulm, of the plant is
looking its best, and when the rows of potatoes, with their elegant rich
foliage and bunches of blossom, have an appearance which would almost
merit their admission to the flower border. The same evening, it may be,
there comes a prolonged thunder storm, followed by a period of hot,
close, moist, muggy weather. Four-and-twenty hours later, the hapless
gardener notices that certain of his potato plants have dark spots upon
some of their leaves. This, he knows too well, is the "plague spot," and
if he examine his plants carefully, he will perhaps find that there is
scarcely a plant which is not spotted. If the thunder shower which we
have imagined be followed by a long period of drought, the plague may be
stayed and the potatoes saved; but if the damp weather continue, the
number of spotted leaves among the potatoes increases day by day, until
the spotted leaves are the majority; and then the haulm dies, gets slimy,
and emits a characteristic odor; and it will be found that the tubers
beneath the soil are but half developed, and impregnated with the disease
to an extent which destroys their value.
Now, the essential cause of the potato disease is perfectly well
understood. It is parasitical, the parasite being a fungus, the
_Peronospora infestans_, which grows at the expense of the leaves, stems,
and tubers of the plant until it destroys their vitality. If a diseased
potato leaf be examined with the naked eye, it will be seen that, on the
upper surface, there is an irregular brownish black spot, and if the
under surface of the leaf be looked at carefully, the brown spot is also
visible, but it will be seen to be covered with a very faint white bloom,
due to the growth of the fungus from the microscopic openings or
"stomata," which exist in large numbers on the under surface of most
green leaves. The microscope shows this "bloom" to be due to the
protrusion of the fungus in the manner stated, and on the free ends of
the minute branches are developed tiny egg shaped vessels, called
"conidia," in which are developed countless "spores," each one of which
is theoretically capable of infecting neighboring plants.
Now, it is right to say that, with respect to the mode of spread of the
disease, scientific men are not quite agreed. All admit that it may be
conveyed by contact, that one leaf may infect its neighbors, and that
birds, flies, rabbits, and other ground game may carry the disease from
one plant to another and from one crop to another. This is insufficient
to account for the sudden onset and the wide extent of potato
"epidemics," which usually attack whole districts at "one fell swoop."
Some of those best qualified to judge believe that the spores are carried
through the air, and I am myself inclined to trust in the opinion
expressed by Mr. William Carruthers, F.R.S., before the select committee
on the potato crop, in 1880. Mr. Carruthers' great scientific
attainments, and his position as the head of the botanical department of
the British Museum, and as the consulting naturalist of the Royal
Agricultural Society, at least demand that his opinion should be received
with the greatest respect and consideration. Mr. Carruthers said (report
on the potato crop, presented to the House of Commons, July 9, 1880,
question 143 _et seq._): "The disease, I believe, did not exist at all in
Europe before 1844.... Many diseases had been observed; many injuries to
potatoes had been observed and carefully described before 1844; but this
particular disease had not. It is due to a species of plant, and although
that species is small, it is as easily separated from allied plants as
species of flowering plants can be separated from each other. This plant
was known in South America before it made its appearance in this country.
It has been traced from South America to North America, and to Australia,
and it made its first appearance in Europe in Belgium, in 1844, and
within a very few days after it appeared in Belgium, it was noticed in
the Isle of Wight, and then within almost a few hours after that it
spread over the whole of the south of England and over Scotland.... When
the disease begins to make its appearance, the fungus produces these
large oblong bodies (_conidia_), and the question is how these bodies are
spread, and the disease scattered.... I believe that these bodies, which
are produced in immense quantities, and very speedily, within a few hours
after the disease attacks the potato, are floating in the atmosphere, and
are easily transplanted by the wind all over the country. I believe this
is the explanation of the spread of the disease in 1844, when it made its
appearance in Belgium. The spores produced in myriads were brought over
in the wind, and first attacked the potato crops in the Isle of Wight,
and then spread over the south of England. The course of the disease is
clearly traced from the south of England toward the midland counties, and
all over the island, and into Scotland and Ireland. It was a progress
northward.... This plant, the _Peronospora infestans_, will only grow on
the _Solanum tuberosum_, that is, the cultivated potato.... Just as
plants of higher organization choose their soils, some growing in the
water and some on land, so the _Peronospora infestans_ chooses its host
plant; and its soil is this species, the _Solatium tuberosum_. It will
not grow if it falls on the leaves of the oak or the beech, or on grass,
because that is not its soil, so to speak. Now, the process of growth is
simply this: When the conidia fall on the leaf, they remain there
perfectly innocent and harmless unless they get a supply of water to
enable them to germinate.... The disease makes its appearance in the end
of July or the beginning of August, when we have, generally, very hot
weather. The temperature of the atmosphere is very high, and we have
heavy showers of rain."
The warmth and moisture are, in fact, the conditions necessary for the
germination of the conidia. Their contents (zoospores) are liberated, and
quickly grow in the leaf, and soon permeate every tissue of the plant.
It was clearly established before the committee that not all potatoes
were equally liable to the disease. The liability depends upon strength
of constitution. It is well known that potatoes are usually, almost
invariably, propagated by "sets," that is, by planting tubers, or
portions of tubers, and this method of propagation is analogous to the
propagation of other forms of plants by means of "cuttings." When
potatoes are raised from seed, it is found that some of the "seedlings"
present a strength of constitution which enables them to resist the
disease for some years, even though the subsequent propagation of the
seedling is entirely from "sets." The raising of seedling potatoes is a
tedious process, but the patience of the grower is often rewarded by
success, and I may allude to the fact that the so-called "Champion
potato," raised from seed in the first instance by Mr. Nicoll, in
Forfarshire, and since propagated all over the country, has enjoyed,
deservedly as it would appear, a great reputation as a disease-resisting
potato; but all who have a practical knowledge of potato growing seem
agreed that we cannot expect its disease-resisting quality to last at
most more than twenty years from its first introduction (in 1877), and
that in time the constitution of the "Champion" will deteriorate, and it
will become a prey to disease.
There is some evidence to show, also, that the constitution of the potato
may be materially influenced by good or bad culture. Damp soils,
insufficient or badly selected manures, the selection of ill developed
potatoes for seed, and the overcrowding of the "sets" in the soil, all
seem to act as causes which predispose the potatoes to the attacks of the
parasite. Strong potatoes resist disease, just as strong children will;
while weak potatoes, equally with weak children, are liable to succumb to
epidemic influences.
The following account of some exact experiments carried out by Mr. George
Murray, of the Botanical Department of the British Museum, seems to show
that Mr. Carruthers' theory as to the diffusion of conidia through the
air is something more than a speculation:
"In the middle of August, 1876," says Mr. Murray, "I instituted the
following experiments, with the object of determining the mode of
diffusion of the conidia of _Peronospora infestans_.
"The method of procedure was to expose on the lee side of a field of
potatoes, of which only about two per cent, were diseased, ordinary
microscopic slides, measuring two inches long by one inch broad, coated
on the exposed surface with a thin layer of glycerine, to which objects
alighting would adhere, and in which, if of the nature of conidia, they
would be preserved. These slides were placed on the projecting stones of
a dry stone wall which surrounded the field, and was at least five yards
from the nearest potato plant. During the five days and nights of the
experiment, a gentle wind blew, and the weather was, on the whole, dry
and clear. Every morning, about nine o'clock, I placed fourteen slides on
the lee side of the field, and every evening, about seven o'clock, I
removed them, and placed others till the following morning at nine
o'clock. The fourteen slides exposed during the day, when examined in the
evening, showed (among other objects):
On the first day. 15 conidia.
" second day. 17 "
" third day. 27 "
" fourth day. 4 "
" fifth day. 9 "
"On none of the five nights did a single conidium alight on the slides.
This seemed to me to prove that during the day the conidia, through the
dryness of the atmosphere and the shaking of the leaves, became detatched
and wafted by the air; while during the night the moisture (in the form
of dew, and on one occasion of a slight and gently falling shower)
prevented the drying of the conidia, and thus rendered them less easy of
detachment.
"I determined the nature of the conidia (1) by comparing them with
authentic conidia directly removed from diseased plants; (2) by there
being attached to some of them portions of the characteristic
conidiaphores; and (3) by cultivating them in a moist chamber, the result
of which was, that five conidia, not having been immersed in the
glycerine, retained their vitality, which they showed by bursting and
producing zoospores in the manner characteristic of _Peronospora
infestans_."
INFLUENZA.
Let us look at another disease by the light of recent knowledge, viz.,
the epidemic influenza, concerning which I remember hearing much talk, as
a child, in 1847-48. There has been no epidemic of this disease in the
British Isles since 1847, but we may judge of its serious nature from the
computation of Peacock that in London alone 250,000 persons were stricken
down with it in the space of a few days. It is characteristic of this
disease that it invades a whole city, or even a whole country, at "one
fell swoop," resembling in its sudden onset and its extent the potato
disease which we have been considering.
The mode of its spreading forbids us to attribute it, at least in any
material degree, although it may be partially so, to contagion in the
ordinary sense, i.e., contagion passing from person to person along the
lines of human intercourse. It forbids us also to look at community of
water supply or food, or the peculiarities of soil, for the source of the
disease virus. We look, naturally, to some atmospheric condition for the
explanation. That the atmosphere is the source of the virus is made more
likely from the fact that the disease has broken out on board ship in a
remarkable way. In 1782, there was an epidemic, and on May 2 in that
year, says Sir Thomas Watson--
"Admiral Kempenfelt sailed from Spithead with a squadron, of which the
Goliah was one. The crew of that vessel were attacked with influenza on
May 29, and the rest were at different times affected; and so many of the
men were rendered incapable of duty by this prevailing sickness, that the
whole squadron was obliged to return into port about the second week in
June, not having had communication with any port, but having cruised
solely between Brest and the Lizard. In the beginning of the same month
another large squadron sailed, all in perfect health, under Lord Howe's
command, for the Dutch coast. Toward the end of the month, just at the
time, therefore, when the Goliah became full of the disease, it appeared
in the Rippon, the Princess Amelia, and other ships of the last mentioned
fleet, although there had been no intercourse with the land."
Similar events were noticed during the epidemic of 1833:
"On April 3, 1833, the very day on which I saw the first two cases that I
did see of influenza--all London being smitten with it on that and the
following day--the Stag was coming up the Channel, and arrived at two
o'clock off Berry Head on the coast of Devonshire, all on board being at
that time well. In half an hour afterward, the breeze being easterly and
blowing off the land, 40 men were down with the influenza, by six o'clock
the number was increased to 60, and by two o'clock the next day to 160.
On the self-same evening a regiment on duty at Portsmouth was in a
perfectly healthy state, but by the next morning so many of the soldiers
of the regiment were affected by the influenza that the garrison duty
could not be performed by it."
After reviewing the various hypotheses which had been put forward to
account for the disease, sudden thaws, fogs, particular winds, swarms of
insects, electrical conditions, ozone, Sir Thomas Watson goes on to say:
"Another hypothesis, more fanciful perhaps at first sight than these, yet
quite as easily accommodated to the known facts of the distemper,
attributes it to the presence of innumerable minute substances, endowed
with vegetable or with animal life, and developed in unusual abundance
under specific states of the atmosphere in which they float, and by which
they are carried hither and thither."
This hypothesis has certainly more facts in support of it now than it had
when Sir Thomas Watson gave utterance to it in 1837. And when another
epidemic of influenza occurs, we may look with some confidence to having
the hypothesis either refuted or confirmed by those engaged in the
systematic study of atmospheric bacteria. Among curious facts in
connection with influenza, quoted by Watson, is the following: "During
the raging of one epidemic, 300 women engaged in coal dredging at
Newcastle, and wading all day in the sea, escaped the complaint." Reading
this, the mind naturally turns to Dr. Blackley's glass slide exposed on
the shore at Filey, and upon which no pollen was deposited, while eighty
pollen grains were deposited on a glass at a higher elevation.
SMALL-POX.
Let us next inquire into the evidence regarding the conveyence of
small-pox through the air. In the supplement to the Tenth Report of the
Local Government Board for 1880-81 (c. 3,290) is a report by Mr. W.H.
Power on the influence of the Fulham, Hospital (for small-pox) on the
neighborhood surrounding it. Mr. Power investigated the incidence of
small-pox on the neighborhood, both before and after the establishment of
the hospital. He found that, in the year included between March, 1876,
and March, 1877, before the establishment of the hospital, the incidence
of small-pox on houses in Chelsea, Fulham and Kensington amounted to 0.41
per cent. (i.e., that one house out of every 244 was attacked by
small-pox in the ordinary way), and that the area inclosed by a circle
having a radius of one mile round the spot where the hospital was
subsequently established (called in the report the "special area") was,
as a matter of fact, rather more free from small-pox than the rest of the
district. After the establishment of the hospital in March, 1877, the
amount of small-pox in the "special area" round the hospital very notably
increased, as is shown by the table by Mr. Power, given below.
This table shows conclusively that the houses nearest the hospital were
in the greatest danger of small-pox. It might naturally be supposed that
the excessive incidence of the disease upon the houses nearest to the
hospital was due to business traffic between the hospital and the
dwellers in the neighborhood, and Mr. Power admits that he started on his
investigation with this belief, but with the prosecution of his work he
found such a theory untenable.
ADMISSIONS OF ACUTE SMALL-POX TO FULHAM HOSPITAL, AND INCIDENCE OF
SMALL-POX UPON HOUSES IN SEVERAL DIVISIONS OF THE SPECIAL AREA DURING
FIVE EPIDEMIC PERIODS.
+-------+---------------------+------------------------------------------------+
| | Incidence on every 100 houses within the |
| | special area and its divisions. |
Cases of|The epidemic periods +--------+---------+---------+---------+---------+
acute |since opening |On total|On small |On first |On second|On third |
small- |of hospital. |special | circle, | ring, | ring, | ring, |
pox. | | area. |0-1/4 mile.|1/4-1/2 mile.|1/2-3/4 mile.|3/4-1 mile.|
--------+---------------------+--------+---------+---------+---------+---------+
327 |March-December 1877 | 1.10 | 3.47 | 1.37 | 1.27 | 0.36 |
714 |January- | | | | | |
| September, 1878 | 1.80 | 4.62 | 2.55 | 1.84 | 0.67 |
679 |September 1878- | | | | | |
| October 1879 | 1.68 | 4.40 | 2.63 | 1.49 | 0.64 |
292 |October, 1879- | | | | | |
| December, 1880 | 0.58 | 1.85 | 1.06 | 0.30 | 0.28 |
515 |December 1880- | | | | | |
| April 1881 | 1.21 | 2.00 | 1.54 | 1.25 | 0.61 |
--------+---------------------+--------+---------+---------+---------+---------+
2,527 |Five periods | 6.37 | 16.34 | 9.15 | 6.15 | 2.56 |
--------+---------------------+--------+---------+---------+---------+---------+
Now, the source of infection in cases of small-pox is often more easy to
find than in cases of some other forms of infectious disease, and mainly
for two reasons:
1. That the onset of small-pox is usually sudden and striking, such as is
not likely to escape observation.
2. That the so-called incubative period is very definite and regular,
being just a fortnight from infection to eruption.
The old experiments of inoculation practiced on our forefathers have
taught us that from inoculation to the first appearance of the rash is
just twelve days. Given a case of small-pox, then one has only to go
carefully over the doings and movements of the patient on the days about
a fortnight preceding in order to succeed very often in finding the
source of infection.
In the fortnight ending February 5, 1881, forty-one houses were attacked
by small-pox in the special mile circle round the hospital, and in this
limited outbreak it was found, as previously, that the severity of
incidence bore an exact inverse proportion to the distance from the
hospital.
The greater part of these were attacked in the five days January 26-30,
1881, and in seeking for the source of infection of these cases, special
attention was directed to the time about a fortnight previous viz.,
January 12-17, 1881. The comings and goings of all who had been directly
connected with the hospital (ambulances, visitors, patients, staff,
nurses, etc.) were especially inquired into, but with an almost negative
result, and Mr. Power was reluctantly forced to the conclusion that
small-pox poison had been disseminated through the air.
During the period when the infection did spread, the atmospheric
conditions were such as would be likely to favor the dissemination of
particulate matter. Mr. Power says: "Familiar illustration of that
conveyance of particulate matter which I am here including in the term
dissemination is seen, summer and winter, in the movements of particles
forming mist and fog. The chief of these are, of course, water particles,
but these carry gently about with them, in an unaltered form, other
matters that have been suspended in the atmosphere, and these other
matters, during the almost absolute stillness attending the formation of
dew and hoar frost, sink earthward, and may often be recognized after
their deposit.
"As to the capacity of fogs to this end, no Londoner needs instruction;
and few persons can have failed to notice the immense distances that
odors will travel on the 'air breaths' of a still summer night. And there
are reasons which require us to believe particulate matter to be more
easy of suspension in an unchanged form during any remarkable calmness of
atmosphere. Even quite conspicuous objects, such as cobwebs, may be held
up in the air under such conditions. Probably there are few observant
persons of rural habits who cannot call to mind one or another still
autumn morning, when from a cloudless, though perhaps hazy, sky, they
have noted, over a wide area, steady descent of countless spider webs,
many of them well-nigh perfect in all details of their construction."
A reference to the meteorological returns issued by the registrar-general
shows that on the 12th of January, 1881, began a period of severe frost,
characterized by still, sometimes foggy, weather, with occasional light
airs from nearly all points of the compass. This state of affairs
continued till January 18, when there was a notable snow storm, and a
gale from the E.N.E. For four days, up to and inclusive of January 8,
ozone was present in more than its usual amounts. During January 9-16, it
was absent. On January 17 it reappeared, and on January 18 it was
abundant. Similar meteorological conditions (calm and no ozone) were
found to precede previous epidemics.
Mr. Power's report, with regard to Fulham, seems conclusive, and there is
a strong impression that hospitals, other than Fulham, have served as
centers of dissemination.
In the last lecture I gave you the opinion of M. Bertillon, of Paris, and
quoted figures in support of that opinion. It is a fact of some
importance to remember that small-pox is one of those diseases which has
a peculiar odor, recognizable by the expert. As to its conveyance for
long distances through the air, there are some curious facts quoted by
Professor Waterhouse, of Cambridge, Massachusetts, in a letter addressed
to Dr. Haygarth at the close of the last century. Professor Waterhouse
states that at Boston there was a small-pox hospital on one side of a
river, and opposite it, 1,500 yards away, was a dockyard, where, on a
certain misty, foggy day, with light airs just moving in a direction from
the hospital to the dockyard, ten men were working. Twelve days later all
but two of these men were down with small-pox, and the only possible
source of infection was the hospital across the river. (_To be
continued_.)
* * * * *
SUNLIGHT COLORS.
[Footnote: Lecture delivered by Capt. W. De W. Abney, R.E., P.B.S., at
the Royal Institution, on February 25, 1887.--_Nature_.]
By Capt. W. DE W. ABNEY.
Sunlight is so intimately woven up with our physical enjoyment of life
that it is perhaps not the most uninteresting subject that can be chosen
for what is--perhaps somewhat pedantically--termed a Friday evening
"discourse." Now, no discourse ought to be be possible without a text on
which to hang one's words, and I think I found a suitable one when
walking with an artist friend from South Kensington Museum the other day.
The sun appeared like a red disk through one of those fogs which the east
wind had brought, and I happened to point it out to him. He looked, and
said, "Why is it that the sun appears so red?" Being near the railway
station, whither he was bound, I had no time to enter into the subject,
but said if he would come to the Royal Institution this evening I would
endeavor to explain the matter. I am going to redeem that promise, and to
devote at all events a portion of the time allotted to me in answering
the question why the sun appears red in a fog. I must first of all appeal
to what every one who frequents this theater is so accustomed, viz., the
spectrum. I am going not to put it in the large and splendid stripe of
the most gorgeous colors before you, with which you are so well
acquainted, but my spectrum will take a more modest form of purer colors,
some twelve inches in length.
I would ask you to notice which color is most luminous. I think that no
one will dispute that in the yellow we have the most intense luminosity,
and that it fades gradually in the red on the one side and in the violet
on the other. This, then, may be called a qualitative estimate of
relative brightnesses; but I wish now to introduce to you what was novel
last year, a quantitative method of measuring the brightness of any part.
Before doing this I must show you the diagram of the apparatus which I
shall employ in some of my experiments.
[Illustration: FIG. 1.--COLOR PHOTOMETER.]
RR are rays (Fig. I) coming from the arc light, or, if we were using
sunlight, from a heliostat, and a solar image is formed by a lens, L_{1},
on the slit, S_{1} of the collimator, C. The parallel rays produced by
the lens, L_{2}, are partially refracted and partially reflected. The
former pass through the prisms, P_{1}P_{2}, and are focused to form a
spectrum by a lens, L_{3}, on D, a movable ground glass screen. The rays
are collected by a lens, L_{4}, tilted at an angle as shown, to form a
white image of the near surface of the second prism on F.
Passing a card with a narrow slit, S_{2}, cut in it in front of the
spectrum, any color which I may require can be isolated. The consequence
is that, instead of the white patch upon the screen, I have a colored
patch, the color of which I can alter to any hue lying between the red
and the violet. Thus, then, we are able to get a real patch of very
approximately homogeneous light to work with, and it is with these
patches of color that I shall have to deal. Is there any way of measuring
the brightness of these patches? was a question asked by General Festing
and myself. After trying various plans, we hit upon the method I shall
now show you, and if any one works with it he must become fascinated with
it on account of its almost childish simplicity--a simplicity, I may
remark, which it took us some months to find out. Placing a rod before
the screen, it casts a black shadow surrounded with a colored background.
Now I may cast another shadow from a candle or an incandescence lamp, and
the two shadows are illuminated, one by the light of the colored patch
and the other by the light from an incandescence lamp which I am using
tonight. [Shown.] Now one stripe is evidently too dark. By an arrangement
which I have of altering the resistance interposed between the battery
and the lamp, I can diminish or increase the light from the lamp, first
making the shadow it illuminates too light and then too dark compared
with the other shadow, which is illuminated by the colored light.
Evidently there is some position in which the shadows are equally
luminous. When that point is reached, I can read off the current which is
passing through the lamp, and having previously standardized it for each
increment of current, I know what amount of light is given out. This
value of the incandescence lamp I can use as an ordinate to a curve, the
scale number which marks the position of the color in the spectrum being
the abscissa. This can be done for each part of the spectrum, and so a
complete curve can be constructed, which we call the illumination curve
of the spectrum of the light under consideration.
Now, when we are working in the laboratory with a steady light, we may be
at ease with this method, but when we come to working with light such as
the sun, in which there may be constant variation, owing to passing, and
may be usually imperceptible, mist, we are met with a difficulty; and in
order to avoid this, General Festing and myself substituted another
method, which I will now show you. We made the comparison light part of
the light we were measuring. Light which enters the collimating lens
partly passes through the prisms and is partly reflected from the first
surface of the prism; that we utilize, thus giving a second shadow. The
reflected rays from P_{1} fall on G, a silver on glass mirror. They are
collected by L_{5}, and form a white image of the prism also at F.
The method we can adopt of altering the intensity of the comparison light
is by means of rotating sectors, which can be opened or closed at will,
and the two shadows thus made equally luminous. [Shown.] But although
this is an excellent plan for some purposes, we have found it better to
adopt a different method. You will recollect that the brightest part of
the spectrum is in the yellow, and that it falls off in brightness on
each side, so instead of opening and closing the sectors, they are set at
fixed intervals, and the slit is moved in front of the spectrum, just
making the shadow cast by the reflected beam too dark or too light, and
oscillating between the two till equality is discovered. The scale number
is then noted, and the curve constructed as before. It must be remembered
that, on each side of the yellow, equality can be established.
This method of securing a comparison light is very much better for sun
work than any other, as any variation in the light whose spectrum is to
be measured affects the comparison light in the same degree. Thus,
suppose I interpose an artificial cloud before the slit of the
spectroscope, having adjusted the two shadows, it will be seen that the
passage of steam in front of the slit does not alter the relative
intensities; but this result must be received with caution. [The lecturer
then proceeded to point out the contrast colors that the shadow of the
rod illuminated by white light assumed.]
I must now make a digression. It must not be assumed that every one has
the same sense of color, otherwise there would be no color blindness.
Part of the researches of General Festing and myself have been on the
subject of color blindness, and these I must briefly refer to. We test
all who come by making them match the luminosity of colors with white
light, as I have now shown you. And as a color blind person has only two
fundamental color perceptions instead of three, his matching of
luminosities is even more accurate than is that made by those whose eyes
are normal or nearly normal. It is curious to note how many people are
more or less deficient in color perception. Some have remarked that it is
impossible that they were color blind and would not believe it, and
sometimes we have been staggered at first with the remarkable manner in
which they recognized color to which they ultimately proved deficient in
perception. For instance, one gentleman when I asked him the name of a
red color patch, said it was sunset color. He then named green and blue
correctly, but when I reverted to the red patch he said green.
On testing further, he proved totally deficient in the color perception
of red, and with a brilliant red patch he matched almost a black shadow.
The diagram shows you the relative perceptions in the spectrum of this
gentleman and myself. There are others who only see three-quarters,
others half, and others a quarter the amount of red that we see, while
some see none. Others see less green and others less violet, but I have
met with no one that can see more than myself or General Festing, whose
color perceptions are almost identical. Hence we have called our curve of
illumination the "normal curve."
We have tested several eminent artists in this manner, and about one half
of the number have been proved to see only three quarters of the amount
of red which we see. It might be thought that this would vitiate their
powers of matching color, but it is not so. They paint what they see; and
although they see less red in a subject, they see the same deficiency in
their pigments; hence they are correct. If totally deficient, the case of
course would be different.
Let us carry our experiments a step further, and see what effect what is
known as a turbid medium has upon the illuminating value of different
parts of the spectrum. I have here water which has been rendered turbid
in a very simple manner. In it has been very cautiously dropped an
alcoholic solution of mastic. Now mastic is practically insoluble in
water, and directly the alcoholic solution comes in contact with the
water it separates out in very fine particles, which, from their very
fineness, remain suspended in the water. I propose now to make an
experiment with this turbid water.
I place a glass cell containing water in front of the slit, and on the
screen I throw a patch of blue light. I now change it for turbid water in
a cell. This thickness much dims the blue; with a still greater thickness
the blue has almost gone. If I measure the intensity of the light at each
operation, I shall find that it diminishes according to a certain law,
which is of the same nature as the law of absorption. For instance, if
one inch diminishes the light one half, the next will diminish it half of
that again, the next half of that again, while the fourth inch will cause
a final diminution of the total light of one sixteenth. If the first inch
allows only one quarter of the light, the next will only allow one
sixteenth, and the fourth inch will only permit 1/256 part to pass.
Let us, however, take a red patch of light and examine it in the same
way. We shall find that, when the greater thickness of the turbid medium
we used when examining the blue patch of light is placed in front of the
slit, much more of this light is allowed to pass than of the blue. If we
measure the light, we shall find that the same law holds good as before,
but that the proportion which passes is invariably greater with the red
than the blue. The question then presents itself: Is there any connection
between the amounts of the red and the blue which pass?
Lord Rayleigh, some years ago, made a theoretical investigation of the
subject. But, as far as I am aware, no definite experimental proof of the
truth of the theory was made till it was tested last year by General
Festing and myself. His law was that for any ray, and through the same
thickness, the light transmitted varied inversely as the fourth power of
the wave length. The wave length 6,000 lies in the red, and the wave
length 4,000 in the violet. Now 6,000 is to 4,000 as 3 to 2, and the
fourth powers of these wave lengths are as 81 to 16, or as about 5 to 1.
If, then, the four inches of our turbid medium allowed three quarters of
this particular red ray to be transmitted, they would only allow (3/4)^{5},
or rather less than one fourth, of the blue ray to pass.
Now, this law is not like the law of absorption for ordinary absorbing
media, such as colored glass for instance, because here we have an
increased loss of light running from the red to the blue, and it matters
not how the medium is made turbid, whether by varnish, suspended sulphur,
or what not. It holds in every case, so long as the particles which make
the medium turbid are small enough. And please to recollect that it
matters not in the least whether the medium which is rendered turbid is
solid, liquid, or air. Sulphur is yellow in mass, and mastic varnish is
nearly white, while tobacco smoke when condensed is black, and very
minute particles of water are colorless; it matters not what the color
is, the loss of light is _always_ the same. The result is simply due to
the scattering of light by fine particles, such particles being small in
dimensions compared with a wave of light. Now, in this trough is
suspended 1/1000 of a cubic inch of mastic varnish, and the water in it
measures about 100 cubic inches, or is 100,000 times more in bulk than
the varnish. Under a microscope of ordinary power it is impossible to
distinguish any particles of varnish; it looks like a homogeneous fluid,
though we know that mastic will not dissolve in water.
Now a wave length in the red is about 1/40000 of an inch, and a little
calculation will show that these particles are well within the necessary
limits. Prof. Tyndall has delighted audiences here with an exposition of
the effect of the scattering of light by small particles in the formation
of artificial skies, and it would be superfluous for me to enter more
into that. Suffice it to say that when particles are small enough to form
the artificial blue sky, they are fully small enough to obey the above
law, and that even larger particles will suffice. We may sum up by saying
that very fine particles scatter more blue light than red light, and that
consequently more red light than blue light passes through a turbid
medium, and that the rays obey the law prescribed by theory.
I will exemplify this once more by using the whole spectrum and placing
this cell, which contains hyposulphite of soda in solution in water, in
front of the slit. By dropping in hydrochloric acid, the sulphur
separates out in minute particles; and you will see that, as the
particles increase in number, the violet, blue, green, and yellow
disappear one by one and only red is left, and finally the red disappears
itself.
Now let me revert to the question why the sun is red at sunset. Those who
are lovers of landscape will have often seen on some bright summer's day
that the most beautiful effects are those in which the distance is almost
of a match to the sky. Distant hills, which when viewed close to are
green or brown, when seen some five or ten miles away appear of a
delicate and delicious, almost of a cobalt, blue color. Now, what is the
cause of this change in color? It is simply that we have a sky formed
between us and the distant ranges, the mere outline of which looms
through it. The shadows are softened so as almost to leave no trace, and
we have what artists call an atmospheric effect. If we go into another
climate, such as Egypt or among the high Alps, we usually lose this
effect. Distant mountains stand out crisp with black shadows, and the
want of atmosphere is much felt. [Photographs showing these differences
were shown.] Let us ask to what this is due. In such climates as England
there is always a certain amount of moisture present in the atmosphere,
and this moisture may be present as very minute particles of water--so
minute indeed that they will sink down in an atmosphere of normal
density--or as vapor. When present as vapor the air is much more
transparent, and it is a common expression to use, that when distant
hills look "so close" rain may be expected shortly to follow, since the
water is present in a state to precipitate in larger particles. But when
present as small particles of water the hills look very distant, owing to
what we may call the haze between us and them. In recent weeks every one
has been able to see very multiplied effects of such haze. The ends of
long streets, for instance, have been scarcely visible, though the sun
may have been shining, and at night the long vistas of gas lamps have
shown light having an increasing redness as they became more distant.
Every one admits the presence of mist on these occasions, and this mist
must be merely a collection of intangible and very minute particles of
suspended water. In a distant landscape we have simply the same or a
smaller quantity of street mist occupying, instead of perhaps 1,000
yards, ten times that distance. Now I would ask, What effect would such a
mist have upon the light of the sun which shone through it?
It is not in the bounds of present possibility to get outside our
atmosphere and measure by the plan I have described to you the different
illuminating values of the different rays, but this we can do: First, we
can measure these values at different altitudes of the sun, and this
means measuring the effect on each ray after passing through different
thicknesses of the atmosphere, either at different times of day or at
different times of the year, about the same hour. Second, by taking the
instrument up to some such elevation as that to which Langley took his
bolometer at Mount Whitney, and so to leave the densest part of the
atmosphere below us.
[Illustration: FIG. 2.--RELATIVE LUMINOSITIES.]
Now, I have adopted both these plans. For more than a year I have taken
measurements of sunlight in my laboratory at South Kensington, and I have
also taken the instrument up to 8,000 feet high in the Alps, and made
observations _there_, and with a result which is satisfactory in that
both sets of observations show that the law which holds with artificially
turbid media is under ordinary circumstances obeyed by sunlight in
passing through our air: which is, you will remember, that more of the
red is transmitted than of the violet, the amount of each depending on
the wave length. The luminosity of the spectrum observed at the Riffel I
have used as my standard luminosity, and compared all others with it. The
result for four days you see in the diagram.
I have diagrammatically shown the amount of different colors which
penetrated on the same days, taking the Riffel as ten. It will be seen
that on December 23 we have really very little violet and less than half
the green, although we have four fifths of the red.
The next diagram before you shows the minimum loss of light which I have
observed for different air thicknesses. On the top we have the calculated
intensities of the different rays outside our atmosphere. Thus we have
that through one atmosphere, and two, three, and four. And you will see
what enormous absorption there is in the blue end at four atmospheres.
The areas of these curves, which give the total luminosity of the light,
are 761, 662, 577, 503, and 439; and if observed as astronomers observe
the absorption of light, by means of stellar observations, they would
have had the values, 761, 664, 578, 504, and 439--a very close
approximation one to the other.
Next notice in the diagram that the top of the curve gradually inclines
to go to the red end of the spectrum as you get the light transmitted
through more and more air, and I should like to show you that this is the
case in a laboratory experiment. Taking a slide with a wide and long slot
in it, a portion is occupied by a right angled prism, one of the angles
of 45 deg. being toward the center of the slot. By sliding this prism in
front of the spectrum I can deflect outward any portion of the spectrum I
like, and by a mirror can reflect it through a second lens, forming a
patch of light on the screen overlapping the patch of light formed by the
undeflected rays. If the two patches be exactly equal, white light is
formed. Now, by placing a rod as before in front of the patch, I have two
colored stripes in a white field, and though the background remains of
the same intensity of white, the intensities of the two stripes can be
altered by moving the right angled prism through the spectrum. The two
stripes are now apparently equally luminous, and I see the point of
equality is where the edge of the right angled prism is in the green.
Placing a narrow cell filled with our turbid medium in front of the slit,
I find that the equality is disturbed, and I have to allow more of the
yellow to come into the patch formed by the blue end of the spectrum, and
consequently less of it in the red end. I again establish equality.
Placing a thicker cell in front, equality is again disturbed, and I have
to have less yellow still in the red half, and more in the blue half. I
now remove the cell, and the inequality of luminosity is still more
glaring. This shows, then, that the rays of maximum luminosity must
travel toward the red as the thickness of the turbid medium is increased.
The observations at 8,000 feet, here recorded, were taken on September
15, at noon, and of course in latitude 46 deg. the sun could not be overhead,
but had to traverse what would be almost exactly equivalent to the
atmosphere at sea level. It is much nearer the calculated intensity for
no atmosphere intervening than it is for one atmosphere. The explanation
of this is easy. The air is denser at sea level than at 8,000 feet up,
and the lower stratum is more likely to hold small water particles or
dust in suspension than is the higher.
[Illustration: FIG. 3.--PROPORTIONS OF TRANSMITTED COLORS.]
For, however small the particles may be, they will have a greater
tendency to sink in a rare air than in a denser one, and less water vapor
can be held per cubic foot. Looking, then, from my laboratory at South
Kensington, we have to look through a proportionately larger quantity of
suspended particles than we have at a high altitude when the air
thicknesses are the same. And consequently the absorption is
proportionately greater at sea level that at 8,000 feet high. This leads
us to the fact that the real intensity of illumination of the different
rays outside the atmosphere is greater than it is calculated from
observations near sea level. Prof. Langley, in this theater, in a
remarkable and interesting lecture, in which he described his journey up
Mount Whitney to about 12,000 feet, told us that the sun was really blue
outside our atmosphere, and at first blush the amount of extra blue which
he deduced to be present in it would, he thought, make it so. But though
he surmised the result from experiments made with rotating disks of
colored paper, he did not, I think, try the method of using pure colors,
and consequently, I believe, slightly exaggerated the blueness which
would result.
I have taken Prof. Langley's calculations of the increase of intensity
for the different rays, which I may say do not quite agree with mine, and
I have prepared a mask which I can place in the spectrum, giving the
different proportions of each ray as calculated by him, and this when
placed in front of the spectrum will show you that the real color of
sunlight outside the atmosphere, as calculated by Langley, can scarcely
be called bluish. Alongside I place a patch of light which is very
closely the color of sunlight on a July day at noon in England. This
comparison will enable you to gauge the blueness, and you will see that
it is not very blue, and, in fact, not bluer perceptibly than that we
have at the Riffel, the color of the sunlight at which place I show in a
similar way. I have also prepared some screens to show you the value of
sunlight after passing through five and ten atmospheres. On an ordinary
clear day you will see what a yellowness there is in the color. It seems
that after a certain amount of blue is present in white light, the
addition of more makes but little difference in the tint. But these last
patches show that the light which passes through the atmosphere when it
is feebly charged with particles does not induce the red of the sun as
seen through a fog. It only requires more suspended particles in any
thickness to induce it.
In observations made at the Riffel, and at 14,000 feet, I have found that
it is possible to see far into the ultra-violet, and to distinguish and
measure lines in the sun's spectrum which can ordinarily only be seen by
the aid of a fluorescent eye piece or by means of photography.
Circumstantial evidence tends to show that the burning of the skin, which
always takes place in these high altitudes in sunlight, is due to the
great increase in the ultra-violet rays. It may be remarked that the same
kind of burning is effected by the electric arc light, which is known to
be very rich in these rays.
Again, to use a homely phrase, "You cannot eat your cake and have it."
You cannot have a large quantity of blue rays present in your direct
sunlight and have a luminous blue sky. The latter must always be light
scattered from the former. Now, in the high Alps you have, on clear day,
a deep blue-black sky, very different indeed from the blue sky of Italy
or of England; and as it is the sky which is the chief agent in lighting
up the shadows, not only in those regions do we have dark shadows on
account of no intervening--what I will call--mist, but because the sky
itself is so little luminous. In an artistic point of view this is
important. The warmth of an English landscape in sunlight is due to the
highest lights being yellowish, and to the shadows being bluish from the
sky light illuminating them. In the high Alps the high lights are colder,
being bluer, and the shadows are dark, and chiefly illuminated by
reflected direct sunlight. Those who have traveled abroad will know what
the effect is. A painting in the Alps, at any high elevation, is rarely
pleasing, although it may be true to nature. It looks cold, and somewhat
harsh and blue.
In London we are often favored with easterly winds, and these, unpleasant
in other ways, are also destructive of that portion of the sunlight which
is the most chemically active on living organisms. The sunlight
composition of a July day may, by the prevalence of an easterly wind, be
reduced to that of a November day, as I have proved by actual
measurement. In this case it is not the water particles which act as
scatterers, but the carbon particles from the smoke.
Knowing, then, the cause of the change in the color of sunlight, we can
make an artificial sunset, in which we have an imitation light passing
through increasing thicknesses of air largely charged with water
particles. [The image of a circular diaphragm placed in front of the
electric light was thrown on the screen in imitation of the sun, and a
cell containing hyposulphite of soda placed in the beam. Hydrochloric
acid was then added; as the fine particles of sulphur were formed, the
disk of light assumed a yellow tint, and as the decomposition of the
hyposulphite progressed, it assumed an orange and finally a deep red
tint.] With this experiment I terminate my lecture, hoping that in some
degree I have answered the question I propounded at the outset--why the
sun is red when seen through a fog.
* * * * *
THE WAVE THEORY OF SOUND CONSIDERED.
By HENRY. A. MOTT, Ph.D., LL.D.
Before presenting any of the numerous difficulties in the way of
accepting the wave theory of sound as correct, it will be best to briefly
represent its teachings, so that the reader will see that the writer is
perfectly familiar with the same.
The wave theory of sound starts off with the assumption that the
atmosphere is _composed of molecules_, and that these supposed molecules
are free to vibrate when acted upon by a vibrating body. When a tuning
fork, for example, is caused to vibrate, it is _assumed_ that the
supposed molecules in front of the advancing fork are crowded closely
together, thus forming a condensation, and on the retreat of the fork are
separated more widely apart, thus forming a rarefaction. On account of
the crowding of the molecules together to form the condensation, the air
is supposed to become more dense and of a higher temperature, while in
the rarefaction the air is supposed to become less dense and of lower
temperature; but the heat of the condensation is supposed to just satisfy
the cold of the rarefaction, in consequence of which the average
temperature of the air remains unchanged.
The supposed increase of temperature in the condensation is supposed to
facilitate the transference of the sound pulse, in consequence of which,
sound is able to travel at the rate of 1,095 feet a second at 0 deg.C., which
it would not do if there was no heat generated.
In other words, the supposed increase of temperature is supposed to add
1/6 to the velocity of sound.
If the tuning fork be a _Koenig C^{3}_ fork, which makes 256 _full_
vibrations in one second, then there will be 256 sound waves in one
second of a length of 1095/256 or 4.23 feet, so that at the end of a
second of time from the commencement of the vibration, the foremost wave
would have reached a distance of 1,095 feet, at 0 deg.C.
The motion of a sound wave must not, however, be confounded with the
motion of the molecules which at any moment form the wave; for during its
passage every molecule concerned in its transference makes only a small
excursion to and fro, the length of the excursion being the amplitude of
vibration, on which the intensity of the sound depends.
Taking the same tuning fork mentioned above, the molecule would take
1/256 of a second to make a full vibration, which is the length of time
it takes for the pulse to travel the length of the sound wave.
For different intensities, the amplitude of vibration of the molecule is
roughly 1/50 to 1/1000000 of an inch. That is to say, in the case of the
same tuning fork, the molecules it causes to vibrate must either travel a
distance of 1/56 or 1/1000000 of an inch forward and back in the 1/256 of
a second or in one direction in the 1/512 of a second.
I might further state that the pitch of the sound depends on the number
of vibrations and the intensity, as already indicated by the amplitude of
stroke--the timbre or quality of the sound depending upon factors which
will be clearly set forth as we advance.
Having now clearly and correctly represented the wave theory of sound,
without touching the physiological effect perceived by means of the ear,
we will proceed to consider it.
We must first consider the state in which the supposed molecules exist
in the air, before making progress.
The present science teaches that the diameter of the supposed molecules
of the air is about 1/250000000 of an inch (Tait); that the distance
between the molecules is about 8/100000 of an inch; that the velocity of
the molecules is about 1,512 feet a second at 0 deg.C., in its free path;
that the number of molecules in a cubic inch at 0 deg.C. is
3,505,519,800,000,000,000 or 35 followed by 17 ciphers (35)^{17}; and
that the number of collisions per second that the molecules make is,
according to Boltzmann, for hydrogen, 17,700,000,000, that is to say, a
hydrogen molecule in one second has its course wholly changed over
seventeen billion times. Assuming seventeen billion or million to be
right for the supposed air molecules, we have a very interesting problem
to consider.
The wave theory of sound requires, if we expect to hear sound by means of
a C^{3} fork of 256 vibrations, that the molecules of the air composing
the sound wave must not be interfered with in such a way as to prevent
them from traveling a distance of at least 1/50 to 1/1000000 of an inch
forward and back in the 1/256 of a second. The problem we have to explain
is, how a molecule traveling at the rate of 1,512 feet a second through a
mean path of 8/100000 of an inch, and colliding seventeen billion or
million times a second, can, by the vibration of the C^{3} fork, be made
to vibrate so as to have a pendulous motion for 1/256 of a second and
vibrate through a distance of 1/50 to the 1/1000000 of an inch without
being changed or mar its harmonic motion.
It is claimed that the range of sound lies between 16 vibrations and
30,000 (about); in such extreme cases the molecules would require 1/16
and 1/30000 of a second to perform the same journey.
It must not be forgotten that a mass moving through a given distance has
the power of doing work, and the amount of energy it will exercise will
depend on _its_ velocity. Now, a molecule of oxygen or nitrogen,
according to modern science, is a _mass_ 1/250000000 of an inch in
diameter, and an oxygen molecule has been calculated to weigh
0.0000000054044 ounce. Taking this weight traveling with a velocity of
1,512 feet a second through an average distance of 8/100000 of an inch,
the battering power or momentum it would have can be shown to be in round
numbers capable of moving 1/200000 of an ounce.
Now, when the C^{3} tuning fork has been vibrating for some time, but
still sounding audibly, Prof. Carter determined that its amplitude of
stroke was only the 1/17000 of an inch, or its velocity of motion was at
the rate of 1/33 of an inch in one second, or one inch in 33 seconds
(over half a minute), or less than one foot in one hour.
Assuming one prong to weigh two ounces, we have a two-ounce mass moving
1/17000 of an inch with a velocity of 1/33 of an inch in one second. The
prong, then, has a momentum or can exercise an amount of energy
equivalent to 1/200 of an ounce, or can overcome the momentum of 1,000
molecules.
It would be difficult to discover not only how a locust can expend
sufficient energy to impart to molecules of the air, so as to set them in
a _forced_ vibration, and thus enable a pulse of the energy imparted to
control the motion of the supposed molecules of the air for a mile in all
directions, but also to estimate the amount of energy the locust must
expend.
According to the wave theory, a condensation and rarefaction are
necessary to constitute a sound wave. Surely, if a condensation is not
produced, there can be no sound wave! We have then no need to consider
anything but the condensation or compression of the supposed air
molecules, which will shorten the discussion. The property of mobility of
the air and fluidity of water are well known. In the case of water, which
is almost incompressible, this property is well marked, and
unquestionably would be very nearly the same if water were wholly
incompressible. In the case of the air, it is conceded by Tyndall,
Thomson, Daniell, Helmholtz, and others that any compression or
condensation of the air must be well marked or defined to secure the
transmission of a sound pulse. The reason for this is on account of this
very property of mobility. Tyndall says: "The prong of the fork in its
swift advancement condenses the air." Thomson says: "If I move my hand
vehemently through the air, I produce a condensation." Helmholtz says:
"The pendulum swings from right to left with a uniform motion. Near to
either end of its path it moves slowly, and in the middle fast. Among
sonorous bodies which move in the same way, only very much faster, we may
mention tuning forks." Tyndall says again: "When a common pendulum
oscillates, it tends to form a condensation in front and a rarefaction
behind. But it is only a tendency; the motion is so slow, and the air so
elastic, that it moves away in front before it is sensibly condensed, and
fills the space behind before it can become sensibly dilated. Hence waves
or pulses are not generated by the pendulum." And finally, Daniell says:
"A vibrating body, _before it can act_ as a sounding body, must produce
alternate compressions and rarefactions in the air, and these must be
well marked. If, however, the vibrating body be so small that at each
oscillation the surrounding air has time to _flow round_ it, there is at
every oscillation a local rearrangement--a local flow and reflow of the
air; but the air at a distance is almost wholly unaffected by this."
Now, as Prof. Carter has shown by experiment that a tuning fork _while
still sounding_ had only an amplitude of swing of 1/17000 of an inch, and
only traveled an aggregate distance of 1/33 of an inch in one second, or
one inch in 33 seconds, surely such a motion is neither "swift," "fast,"
nor "vehement," and is unquestionably much "slower" than the motion of a
pendulum. We have only to consider one forward motion of the prong, and
if that motion cannot condense the air, then no wave can be produced; for
after a prong has advanced and stopped moving (no matter for how short a
time), if it has not compressed the air, its return motion (on the same
side) cannot do anything toward making a compression. If one such motion
of 1/17000 of an inch in 1/512 of a second cannot compress the air, then
the remaining motions cannot. There is unquestionably a "union limit"
between mobility and compressibility, and unless this limit is passed,
mobility holds sway and prevents condensation or compression of the air;
but when this limit is passed by the exercise of sufficient energy, then
compression of the air results. Just imagine the finger to be moved
through the air at a velocity of one foot in one hour; is it possible
that any scientist who considers the problem in connection with the
mobility of the air, could risk his reputation by saying that the air
would be compressed? Heretofore it was supposed that a praeong of a tuning
fork was traveling _fast_ because it vibrated so many times in a second,
never stopping to think that its velocity of motion was entirely
dependent upon the distance it traveled. At the start the prong travels
1/20 of an inch, but in a short time, _while still sounding_, the
distance is reduced to 1/17000 of an inch. While the first motion was
quite fast, about 25 inches in a second, the last motion was only about
1/33 of an inch in the same time, and is consequently 825 times slower
motion. The momentum of the prong, the amount of work it can do, is
likewise proportionately reduced.
Some seem to imagine, without thinking, that the elasticity of the air
can add additional energy. This is perfectly erroneous; for elasticity is
a mere property, which permits a body to be compressed on the application
of a force, and to be dilated by the exercise of the force stored up in
it by the compression. No property of the air can impart any energy. If
the momentum of a molecule or a series of molecules extending in all
directions for a mile is to be overcome so as to control the character of
the movements of the molecules, then sufficient _external_ energy must be
applied to accomplish the task: and when we think that one cubic inch of
air contains 3,505,519,800,000,000,000 molecules, to say nothing about
the number in a cubic mile, which a locust can transmit sound through, we
are naturally compelled to stop and think whether the vibrations of
_supposed_ molecules have anything or can have anything to do with the
transference of sound through the air.
If control was only had of the distance the vibrating molecule travels
from its start to the end of its journey, then only the intensity of the
sound would be under subjection; but if at every _infinitesimal instant_
control was had of its amplitude of swing, then the character, timbre, or
quality of the sound is under subjection. It is evident, then, that the
blows normally given by one molecule to another in their supposed
constant bombardment must not be sufficient to alter the character of
vibration a molecule set in oscillation by a sounding body must maintain,
to preserve the timbre or quality of the sound in process of
transmission; for if any such alteration should take place, then,
naturally, while the pitch, and perhaps intensity, might be transmitted,
the quality of the sound would be destroyed.
Again, it is certain that no molecule can perform two sets of vibrations,
two separate movements, at the same time, any more than it can be in two
places at the same time.
When a band of music is playing, the molecule is supposed to make a
complex vibration, a resultant motion of all acting influences, which the
ear is supposed to analyze. It remains for the mathematician to show how
a molecule influenced by twenty or more degrees of applied energy, and
twenty or more required number of frequences of vibration at the same
time, can establish a resultant motion which will transmit the required
pitch, intensity, and timbre of each instrument.
When a molecule is acted on by various forces, a resultant motion is
unquestionably produced, but this would only tend to send the molecule
forward and back in _one_ direction, and, in fact, a direction it might
have taken in the first place if hit properly.
How any resultant can be established as regards the time necessary for
the molecule to take so as to complete a full vibration for the note
C_{11}, which requires 1/16 of a second, and for other notes up to
C''''', which only requires 1/4176 of a second, as when an orchestra is
playing, is certainly beyond human comprehension, if it is not beyond the
"transcendental mathematics" of the present day.
Unquestionably, the able mathematicians Lord Rayleigh, Stokes, or
Maxwell, if the problem was submitted to them, would start directly to
work, and deduce by so called "higher mathematics" the required motions
the molecules would have to undergo to accomplish this marvelous
task--the same as they have established the diameter of the _supposed_
molecules, their velocity, distance apart, and number of bombardments,
without any shadow of _positive_ proof that any such things as molecules
exist.
As S. Caunizzana has said: "Some of the followers of the modern school
push their faith to the borders of fanaticism; they often speak on
molecular subjects with as much dogmatic assurance as though they had
actually realized the ingenious fiction of Laplace, and had constructed a
microscope by which they could detect the molecule and count the number
of its constituent atoms."
Speaking of the "modern manufacturers of mathematical hypotheses,"
Mattieu Williams says: "It matters not to them how 'wild and visionary,'
how utterly gratuitous, any assumption may be, it is not unscientific
provided it can be vested in formulae and worked out mathematically.
"These transcendental mathematicians are struggling to carry philosophy
back to the era of Duns Scotus, when the greatest triumph of learning was
to sophisticate so profoundly an obvious absurdity that no ordinary
intellect could refute it.... The close study of _pure_ mathematics, by
directing the mind to processes of calculation rather than to phenomena,
induces that sublime indifference to facts which has characterized the
purely mathematical intellect of all ages."
Tyndall, however, states in all frankness, and without the aid of
mathematical considerations, that "when we try to visualize the motions
of the air having one thousand separate tones, to present to the eye of
the mind the battling of the pulses, direct and reverberated, the
imagination retires baffled at the attempt;" and he might have added, the
shallowness and fallacy of the wave theory of sound was made apparent.
He, however, does express himself as follows: "Assuredly, no question of
science ever stood so much in need of revision as this of the
transmission of sound through the atmosphere. Slowly but surely we
mastered the question, and the further we advance, the more plainly it
appeared that our reputed knowledge regarding it was erroneous from
beginning to end."
Until physicists are willing to admit that the physical forces of nature
are objective things--actual entities, and not mere modes of motion--a
full and clear comprehension of the phenomena of nature will never be
revealed to them. The motion of all bodies, whether small or great, is
due to the entitative force stored up in them, and the energy they
exercise is in proportion to the stored-up force.
Tyndall says that "_heat itself_, its _essence and quiddity_, IS MOTION,
AND NOTHING ELSE." Surely, no scientist who considers what motion is can
admit such a fallacious statement, for motion is simply "position in
space changing;" it is a phenomenon, the result of the application of
entitative force to a body. It is no more an entity than shadow, which is
likewise a phenomenon. Motion, _per se_, is nothing and can do nothing in
physics. Matter and force are the two great entities of the
universe--both being objective things. Sound, heat, light, electricity,
etc., are different forms of manifestation of an all-pervading force
element--substantial, yet not material.
* * * * *
[NATURE.]
THE RELATION OF TABASHEER TO MINERAL SUBSTANCES.
Mr. Thiselton Dyer has rendered a great service, not only to botanists,
but also to physicists and mineralogists, by recalling attention to the
very interesting substance known as "tabasheer." As he truly states, very
little fresh information has been published on the subject during recent
years, a circumstance for which I can only account by the fact that
botanists may justly feel some doubt as to whether it belongs to the
vegetable kingdom, while mineralogists seem to have equal ground for
hesitation in accepting it as a member of the mineral kingdom.
It is very interesting to hear that so able a physiologist as Prof. Cohn
intends to investigate the conditions under which living plants separate
this substance from their tissues. That unicellular algae, like the
Diatomaceae, living in a medium which may contain only one part in 10,000
by weight of dissolved silica, or even less than that amount, should be
able to separate this substance to form their exquisitely ornamented
frustules is one of the most striking facts in natural history, whether
we regard it in its physiological or its chemical aspects.
Sir David Brewster long ago pointed out the remarkable physical
characters presented by the curious product of the vegetable world known
as "tabasheer," though so far as I can find out it has not in recent
years received that attention from physicists which the experiments and
observations of the great Scotch philosopher show it to be worthy of.
Tabasheer seems to stand in the same relation to the mineral kingdom as
do ambers and pearls. It is in fact an _opal_ formed under somewhat
remarkable and anomalous conditions which we are able to study; and in
this aspect I have for some time past been devoting a considerable amount
of attention to the minute structure of the substance by making thin
sections and examining them under the microscope. It may be as well,
perhaps, to give a short sketch of the information upon the subject which
I have up to the present time been able to obtain, and in this way to
call attention to points upon which further research seems to be
necessary.
From time immemorial tabasheer has enjoyed a very high reputation in
Eastern countries as a drug. Its supposed medicinal virtues, like those
of the fossil teeth of China and the belemnites ("thunderbolts") of this
country, seem to have been suggested by the peculiarity of its mode of
occurrence. A knowledge of the substance was introduced into Western
Europe by the Arabian physicians, and the name by which the substance is
generally known is said to be of Arabic origin. Much of the material
which under the name of "tabasheer" finds its way to Syria and Turkey is
said, however, to be fictitious or adulterated.
In 1788 Dr. Patrick Russell, F.R.S., then resident at Vizagapatam, wrote
a letter to Sir Joseph Banks in which he gave an account of all the facts
which he had been able to collect with respect to this curious substance
and its mode of occurrence, and his interesting letter was published in
the Philosophical Transactions for 1790 (vol. lxxx., p. 273).
Tabasheer is said to be sometimes found among the ashes of bamboos that
have been set on fire (by mutual friction?). Ordinarily, however, it is
sought for by splitting open those bamboo stems which give a rattling
sound when shaken. Such rattling sounds do not, however, afford
infallible criteria as to the presence or absence of tabasheer in a
bamboo, for where the quantity is small it is often found to be closely
adherent to the bottom and sides of the cavity. Tabasheer is by no means
found in all stems or in all joints of the same stem of the bamboos.
Whether certain species produce it in greater abundance than others, and
what is the influence of soil, situation, and season upon the production
of the substance, are questions which do not seem as yet to have been
accurately investigated.
Dr. Russell found that the bamboos which produce tabasheer often contain
a fluid, usually clear, transparent, and colorless or of greenish tint,
but sometimes thicker and of a white color, and at other times darker and
of the consistency of honey. Occasionally the thicker varieties were
found passing into a solid state, and forming tabasheer.
Dr. Russell performed the interesting experiment of drawing off the
liquid from the bamboo stem and allowing it to stand in stoppered
bottles. A "whitish, cottony sediment" was formed at the bottom, with a
thin film of the same kind at the top. When the whole was well shaken
together and allowed to evaporate, it left a residue of a whitish brown
color resembling the inferior kinds of tabasheer. By splitting up
different joints of bamboo Dr. Russell was also able to satisfy himself
of the gradual deposition within them of the solid tabasheer by the
evaporation of the liquid solvent.
In 1791, Mr. James Louis Macie, F.R.S. (who afterward took the name of
Smithson), gave an account of his examination of the properties of the
specimens of tabasheer sent home by Dr. Russell (Phil. Trans., vol.
lxxxi., 1791, p. 368). These specimens came from Vellore, Hyderabad,
Masulipatam, and other localities in India. They were submitted to a
number of tests which induced Mr. Macie to believe that they consisted
principally of silica, but that before calcination some vegetable matter
must have been present. A determination of the specific gravity of the
substance by Mr. Macie gave 2.188 as the result. Another determination by
Mr. Cavendish gave 2.169.
In this same paper it is stated that a bamboo grown in a hot-house at
Islington gave a rattling noise, and on being split open by Sir Joseph
Banks yielded, not an ordinary tabasheer, but a small pebble about the
size of half a pea, externally of a dark brown or black color, and
within of a reddish brown tint. This stone is said to have been so hard
as to cut glass, and to have been in parts of a crystalline structure.
Its behavior with reagents was found to be different in many respects
from that of the ordinary tabasheer; and it was proved to contain silica
and iron. The specimen is referred to in a letter to Berthollet published
in the _Annales de Chimie_ for the same year (October, 1791). There may
be some doubt as to whether this specimen was really of the nature of
tabasheer. If such were the case, it would seem to have been a tabasheer
in which a crystalline structure had begun to be set up.
In the year 1806, MM. Foureroy and Vauquelin gave an account of a
specimen of tabasheer brought from South America in 1804 by Humboldt and
Bonpland (_Mem. de l'Inst_., vol. vi., p. 382). It was procured from a
species of bamboo growing on the west of Pichincha, and is described as
being of a milk white color, in part apparently crystalline in structure,
and in part semi-transparent and gelatinous. It was seen to contain
traces of the vegetable structure of the plant from which it had been
extracted. On ignition it became black, and emitted pungent fumes.
An analysis of this tabasheer from the Andes showed that it contained 70
per cent. of silica and 30 per cent. of potash, lime, and water, with
some organic matter. It would, perhaps, be rash to conclude from this
single observation that the American bamboo produced tabasheer of
different composition from that of the Old World; but the subject is
evidently one worthy of careful investigation.
It was in the year 1819 that Sir David Brewster published the first
account of his long and important series of observations upon the
physical peculiarities of tabasheer (Phil. Trans., vol. cix., 1819, p.
283). The specimens which he first examined were obtained from India by
Dr. Kennedy, by whom they were given to Brewster.
Brewster found the specimens which he examined to be perfectly
_isotropic_, exercising no influence in depolarizing light. When heated,
however, it proved to be remarkably _phosphorescent_. The translucent
varieties were found to transmit a yellowish and to reflect a bluish
white light--or, in other words, to exhibit the phenomenon of
_opalescence_. When tabasheer is slightly wetted, it becomes white and
opaque; but when thoroughly saturated with water, perfectly transparent.
By preparing prisms of different varieties of tabasheer, Brewster
proceeded to determine its refractive index, arriving at the remarkable
result that tabasheer "has a lower index of refraction than any other
known solid or liquid, and that it actually holds an intermediate place
between water and gaseous bodies!" This excessively low refractive power
Brewster believes to afford a complete explanation of the extraordinary
behavior exhibited by tabasheer when wholly or partially saturated with
fluids. A number of interesting experiments were performed by saturating
the tabasheer with oils of different refractive powers, and by heating it
in various ways and under different conditions, and also by introducing
carbonaceous matter into the minute pores of the substance by setting
fire to paper in which fragments were wrapped.
The mean of experiments undertaken by Mr. James Jardine, on behalf of
Brewster, for determining the specific gravity of tabasheer, gave as a
result 2.235. From these experiments Brewster concluded that the space
occupied by the pores of the tabasheer is about two and a half times as
great as that of the colloid silica itself!
From this time forward Brewster seems to have manifested the keenest
interest in all questions connected with the origin and history of a
substance possessing such singular physical properties. By the aid of Mr.
Swinton, secretary to the government at Calcutta, he formed a large and
interesting collection of all the different varieties of tabasheer from
various parts of India. He also obtained specimens of the bamboo with the
tabasheer _in situ_. In 1828 he published an interesting paper on "The
Natural History and Properties of Tabasheer" (_Edinburgh Journal of
Science_, vol. viii., 1828, p. 288), in which he discussed many of the
important problems connected with the origin of the substance. From his
inquiries and observations, Brewster was led to conclude that tabasheer
was only produced in those joints of bamboos which are in an injured,
unhealthy, or malformed condition, and that the siliceous fluid only
finds its way into the hollow spaces between the joints of the stem when
the membrane lining the cavities is destroyed or rent by disease.
Prof. Edward Turner, of the University of London, undertook an analysis
of tabasheer, the specimens being supplied from Brewster's collection
(_Edinburgh Journal of Science_, vol. viii., 1828, p. 335). His
determinations of the specific gravities of different varieties were as
follows:
Chalky tabasheer. 2.189
Translucent tabasheer. 2.167
Transparent tabasheer. 2.160
All the varieties lose air and hygroscopic water at 100 deg. C., and a larger
quantity of water and organic matter (indicated by faint smoke and an
empyreumatic odor) at a red heat. The results obtained were as follows:
Loss at 100 deg. C. Loss at red heat.
Chalky tabasheer. 0.838 per cent. 1.277 per cent.
Translucent tabasheer. 1.620 " " 3.840 " "
Transparent tabasheer. 2.411 " " 4.518 " "
Dr. Turner found the ignited Indian tabasheer to consist almost entirely
of pure silica with a minute quantity of lime and vegetable matter. He
failed to find any trace of alkalies in it.
In 1855, Guibourt (_Journ. de Pharm_. [3], xxvii., 81, 161, 252; _Phil.
Mag_, [4], x., 229) analyzed a specimen of tabasheer having a specific
gravity of 2.148. It gave the following result:
Silica. = 96.94
Potash and lime. = 0.13
Water. = 2.93
Organic matter. = trace
Guibourt criticised some of the conclusions arrived at by Brewster, and
sought to explain the source of the silica by studying the composition of
different parts of the bamboo. While the ashes of the wood contained
0.0612 of the whole weight of the wood, the pith was found to contain
0.448 per cent., the inner wood much less, and the greatest proportion
occurred in the external wood. On these determinations Guibourt founded a
theory of the mode of formation of tabasheer based on the suggestion that
at certain periods of its growth the bamboo needed less silica than at
other times, and that when not needed, the silica was carried inward and
deposited in the interior.
In the year 1857, D.W. Host van Tonningen, of Buitenzorg, undertook an
investigation of the tabasheer of Java, which is known to the natives of
that island under the name of "singkara" (_Naturkundig Tijdschrift voor
Nederlandsch Indie_, vol. xiii., 1857, p. 391). The specimens examined
were obtained from the _Bambusa apus_, growing in the Residency of
Bantam. It is described as resembling in appearance the Indian
tabasheers. Its analysis gave the following result:
Silica. = 86.387
Iron oxide. = 0.424
Lime. = 0.244
Potash. = 4.806
Organic matter. = 0.507
Water. = 7.632
------
Total. 100.000
Apart from the question of its singular mode of origin, however, and its
remarkable and anomalous physical properties, tabasheer is of much
interest to mineralogists and geologists. All the varieties hitherto
examined, with the exception of the peculiar one from the Andes, are in
composition and physical characters true opals. This is the case with all
the Indian and Java varieties. They consist essentially of silica in its
colloidal form, the water, lime, potash, and organic matter being as
small and variable in amount as in the mineral opals; and, as in them,
these substances must be regarded merely as mechanical impurities.
The tabasheers must be studied in their relations on the one hand with
certain varieties of the natural semi-opals, hydrophanes, beekites, and
floatstones, some of which they closely resemble in their physical
characters, and on the other hand with specimens of artificially
deposited colloid silica formed under different conditions. Prof. Church,
who has so successfully studied the beekites, informs me that some of
those remarkable bodies present singular points of analogy with
tabasheer.
By the study of thin sections I have, during several years, been
endeavoring to trace the minute structure of some of these substances. In
no class of materials is it more necessary to guard one's self against
errors of observation arising from changes induced in the substance
during the operations which are necessary to the preparation of
transparent sections of hard substances. Unfortunately, too, it is the
custom of the natives to prepare the substance for the market by an
imperfect calcination, and hitherto I have only been able to study
specimens procured in the markets which have been subjected to this
process. It is obviously desirable, before attempting to interpret the
structures exhibited, under the microscope, to compare the fresh and
uncalcined materials with those that have been more or less altered by
heat.
Tabasheer would seem, from Brewster's experiments, to be a very intimate
admixture of two and a half parts of air with one part of colloidal
silica. The interspaces filled with air appear, at all events, in most
cases, to be so minute that they cannot be detected by the highest powers
of the microscope which I have been able to employ. It is this intimate
admixture of a solid with a gas which probably gives rise to the curious
and anomalous properties exhibited by this singular substance.
The ultra-microscopical vesicles filled with air in all probability give
rise to the opalescence which is so marked a property of the substance.
Their size is such as to scatter and throw back the rays at the blue end
of the spectrum and to transmit those at the red end.
When the vesicles of the substance are filled with Canada balsam, and a
thin slice is cut from it, this opalescence comes out in the most
striking manner. Very thin sections are of a rich orange yellow by
transmitted light, and a delicate blue tint by reflected light. I do not
know of any substance which in such thin films displays such striking
opalescence.
That the excessively low refractive power of tabasheer is connected with
the mechanical admixture of the colloidal silica with air seems to be
proved by the experiments of Brewster, showing that with increase of
density there was an increase in the refractive index from 1.111 in
specimens of the lowest specific gravity to 1.182 in those of the highest
specific gravity. Where the surface was hard and dense, Brewster found
the refractive index to approach that of semi opal. The wonderful thing
is that a substance so full of cavities containing gas should
nevertheless be transparent.
By the kindness of Mr. F. Rutley, F.G.S., I am able to supply a drawing
taken from one of my sections of tabasheer.
The accompanying woodcut gives some idea of the interesting structures
exhibited in some sections of tabasheer, though much of the delicacy and
fidelity of the original drawing has been lost in transferring it to the
wood.
In this particular case, the faint punctation of the surface may possibly
indicate the presence of air vesicles of a size sufficiently great to be
visible under the microscope. But in many other instances I have failed
to detect any such indication, even with much higher powers. The small
ramifying tubules might at first sight be taken for some traces of a
vegetable tissue, but my colleague, Dr. Scott, assures me that they do
not in the least resemble any tissue found in the bamboo. I have myself
no doubt that it is an inorganic structure. It is not improbably
analogous to the peculiar ramifying tubules formed in a solution of water
glass when a crystal of copper sulphate is suspended in it, as shown by
Dr. Heaton (Proc. Brit. Assoc., 1869, p. 127). Similar forms also occur
on a larger scale in some agates, and the artificial cells of Traube may
probably be regarded as analogous phenomena.
The aggregates of globular bodies seen in the section so greatly resemble
the globulites of slags and natural glasses, and in their arrangement so
forcibly recall the structures seen in the well known pitchstone of
Corriegills in Arran, that one is tempted to regard them as indicating
the beginnings of the development of crystalline structure in the
tabasheer. But I have good grounds for believing the structure to have a
totally different origin. They seem in fact to be the portions of the
mass which the fluid Canada balsam has not succeeded in penetrating. By
heating they may be made to grow outward, and as more balsam is imbibed
they gradually diminish, and finally disappear.
I must postpone till a future occasion a discussion of all the structures
of this remarkable substance and of the resemblances and differences
which they present to the mineral opals on the one hand, and to those of
the opals of animal origin found in sponge spicules, radiolarians, and
the rocks formed from them, some of which have recently been admirably
investigated by Dr. G.J. Hinde (Phil. Trans., 1885, pp. 425-83).
I cannot, however, but think that it would be of the greatest service to
botanists, physicists, and mineralogists alike, if some resident in India
would resume the investigations so admirably commenced by Dr. Patrick
Russell nearly a century ago; and it is in the hope of inducing some one
to undertake this task that I have put together these notes. There are
certain problems with regard to the mode of occurrence of this singular
substance which could only be solved by an investigator in the country
where it is found.
[Illustration: SECTION OF INDIAN TABASHEER, SEEN WITH A MAGNIFYING POWER OF
250 DIAMETERS.]
Most parcels of the commercial tabasheer appear to contain different
varieties, from the white, opaque, chalk like forms through the
translucent kinds to those that are perfectly transparent. It would be of
much interest if the exact relation and modes of origin of these
different varieties could be traced. It would also be important to
determine if Brewster was right in his conclusion that the particular
internodes of a bamboo which contain tabasheer always have their inner
lining tissue rent or injured. The repetition of Dr. Russell's experiment
of drawing off the liquids from the joints of bamboos and allowing them
to evaporate is also greatly to be desired. My colleague, Prof. Rucker,
F.R.S., has kindly undertaken to re-examine the results arrived at by
Brewster in the light of more recent physical investigations, and I doubt
not that some of the curious problems suggested by this very remarkable
substance may ere long find a solution.
JOHN W. JUDD.
* * * * *
THE EDIBLE EARTH OF JAVA.
In 1883 Mr. Hekmeyer, pharmaceutist in chief of the Dutch Indies,
exhibited at Amsterdam some specimens of Javanese edible earth, both in a
natural state and in the form of various natural objects. A portion of
this collection he has placed at our disposal, and has given us some
information regarding its nature, use, etc.
These clays, which are eaten not only in Java, but also in Sumatra, New
Caledonia, Siberia, Guiana, Terra del Fuego, etc., are essentially
composed of silex, alumina, and water in variable proportions, and are
colored with various metallic oxides. They are in amorphous masses, are
unctuous to the touch, stick to the tongue, and form a fine, smooth paste
with water. The natives of Java and Sumatra prepare them in a peculiar
way. They free them of foreign substances, spread them out in thin
sheets, which they cut into small pieces and parch in an iron saucepan
over a coal fire.
Each of these little cakes, when shrunken up into a little roll, looks
somewhat like a grayish or reddish fragment of cinnamon bark. The clay is
also formed into imitations of various objects.
We have tasted this Javanese dainty, and we must very humbly confess that
we have found nothing attractive in the earthy and slightly empyreumatic
taste of this singular food. However, a sweet and slightly aromatic taste
that follows the first impression is an extenuating circumstance.
According to the account given by Labillardiere, confirmed by the
information given by Mr. Hekmeyer, the figures are often craunched by
women and children, to the latter of whom they serve as dolls, toys, and
even money-boxes, as shown by the slits formed in the upper part of the
larger objects, which are usually hollow.
We have not sufficient documents to carry us back to the origin of that
tradition that would have it that the human form has been given to
certain food preparations from remote times. Savants will not be slow to
see in this a vague relic of the horrible festivities that succeeded
human sacrifices among primitive peoples. For want of prisoners and of
designated victims, a symbolic representation would have gradually
developed, and been kept up, though losing its religious character. We
merely call brief attention to this obscure problem, not having the
pretension to solve it.--_Revue d'Ethnographie_.
* * * * *
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