The Botanic Garden
by
Erasmus Darwin
Part 4 out of 7
There is an apple described in Bradley's work which is said to have one
side of it a sweet fruit which boils soft, and the other side a sour
fruit which boils hard, which Mr. Bradley so long ago as the year 1721
ingeniously ascribes to the farina of one of these apples impregnating
the other, which would seem the more probable if we consider that each
division of an apple is a separate womb, and may therefore have a
separate impregnation like puppies of different kinds in one litter. The
same is said to have occurred in oranges and lemons, and grapes of
different colours.]
485 "Thus when in holy triumph Aaron trod,
And offer'd on the shrine his mystic rod;
First a new bark its silken tissue weaves,
New buds emerging widen into leaves;
Fair fruits protrude, enascent flowers expand,
490 And blush and tremble round the living wand.
XIII. 1. "SYLPHS! on each Oak-bud wound the wormy galls,
With pigmy spears, or crush the venom'd balls;
Fright the green Locust from his foamy bed,
Unweave the Caterpillar's gluey thread;
495 Chase the fierce Earwig, scare the bloated Toad,
Arrest the snail upon his slimy road;
Arm with sharp thorns the Sweet-brier's tender wood,
And dash the Cynips from her damask bud;
Steep in ambrosial dews the Woodbine's bells,
500 And drive the Night-moth from her honey'd cells.
So where the Humming-bird in Chili's bowers
On murmuring pinions robs the pendent flowers;
Seeks, where fine pores their dulcet balm distill,
And sucks the treasure with proboscis-bill;
505 Fair CYPREPEDIA with successful guile
Knits her smooth brow, extinguishes her smile;
A Spiders bloated paunch and jointed arms
Hide her fine form, and mask her blushing charms;
In ambush sly the mimic warrior lies,
510 And on quick wing the panting plunderer flies.
[_Fair Cyprepedia_. l. 505. The cyprepedium from South America is
supposed to be of larger size and brighter colours than that from North
America from which this print is taken; it has a large globular nectary
about the size of a pidgeon's egg of a fleshy colour, and an incision or
depression on its upper part, much resembling the body of the large
American spider; this globular nectary is attached to divergent slender
petals not unlike the legs of the same animal. This spider is called by
Linneus Arenea avicularia, with a convex orbicular thorax, the center
transversely excavated, he adds that it catches small birds as well as
insects, and has the venemous bite of a serpent. System Nature, Tom. I.
p. 1034. M. Lonvilliers de Poincy, (Histoire Nat. des Antilles, Cap.
xiv. art. III.) calls it Phalange, and describes the body to be the size
of a pidgeon's egg, with a hollow on its back like a navel, and mentions
its catching the humming-bird in its strong nets.
The similitude of this flower to this great spider seems to be a
vegetable contrivance to prevent the humming-bird from plundering its
honey. About Matlock in Derbyshire the fly-ophris is produced, the
nectary of which so much resembles the small wall-bee, perhaps the apis
ichneumonea, that it may be easily mistaken for it at a small distance.
It is probable that by this means it may often escape being plundered.
See note on lonicera in the next poem.
A bird of our own country called a willow-wren (Motacilla) runs up the
stem of the crown-imperial (Frittillaria coronalis) and sips the
pendulous drops within its petals. This species of Motacilla is called
by Ray Regulus non cristatus. White's Hist. of Selborne.]
[Illustration: _Cypripedium. London, Published Dec'r 1st 1791 by J.
Johnson, St. Paul's Church Yard._]
2. "Shield the young Harvest from devouring blight,
The Smut's dark poison, and the Mildew white;
Deep-rooted Mould, and Ergot's horn uncouth,
And break the Canker's desolating tooth.
515 First in one point the festering wound confin'd
Mines unperceived beneath the shrivel'd rin'd;
Then climbs the branches with increasing strength,
Spreads as they spread, and lengthens with their length;
--Thus the slight wound ingraved on glass unneal'd
520 Runs in white lines along the lucid field;
Crack follows crack, to laws elastic just,
And the frail fabric shivers into dust.
[_Shield the young harvest_. l. 511. Linneus enumerates but four
diseases of plants; Erysyche, the white mucor or mould, with sessile
tawny heads, with which the leaves are sprinkled, as is frequent on the
hop, humulus, maple, acer, &c. Rubigo, the ferrugineous powder sprinkled
under the leaves frequent in lady's mantle, alchemilla, &c.
Clavus, when the seeds grow out into larger horns black without, as in
rye. This is called Ergot by the french writers.
Ustulago, when the fruit instead of seed produces a black powder, as in
barley, oats, &c. To which perhaps the honey-dew ought to have been
added, and the canker, in the former of which the nourishing fluid of
the plant seems to be exsuded by a retrograde motion of the cutaneous
lymphatics, as in the sweating sickness of the last century. The latter
is a phagedenic ulcer of the bark, very destructive to young apple-
trees, and which in cherry-trees is attended with a deposition of gum
arabic, which often terminates in the death of the tree.]
[_Ergot's horn_. l. 513. There is a disease frequently affects the rye
in France, and sometimes in England in moist seasons, which is called
Ergot, or horn seed; the grain becomes considerably elongated and is
either straight or crooked, containing black meal along with the white,
and appears to be pierced by insects, which were probably the cause of
the disease. Mr. Duhamel ascribes it to this cause, and compares it to
galls on oak-leaves. By the use of this bad grain amongst the poor
diseases have been produced attended with great debility and
mortification of the extremities both in France and England. Dict.
Raison. art. Siegle. Philosop. Transact.]
[_On glass unneal'd_. l. 519. The glass makers occasionally make what
they call _proofs_, which are cooled hastily, whereas the other glass
vessels are removed from warmer ovens to cooler ones, and suffered to
cool by slow degrees, which is called annealing, or nealing them. If an
unnealed glass be scratched by even a grain of sand falling into it, it
will seem to consider of it for some time, or even a day, and will then
crack into a thousand pieces.
The same happens to a smooth surfaced lead-ore in Derbyshire, the
workmen having cleared a large face of it scratch it with picks, and in
a few hours many tons of it crack to pieces and fall, with a kind of
explosion. Whitehurst's Theory of Earth.
Glass dropped into cold water, called Prince Rupert's drops, explode
when a small part of their tails are broken off, more suddenly indeed,
but probably from the same cause. Are the internal particles of these
elastic bodies kept so far from each other by the external crust that
they are nearly in a state of repulsion into which state they are thrown
by their vibrations from any violence applied? Or, like elastic balls in
certain proportions suspended in contact with each other, can motion
once began be increased by their elasticity, till the whole explodes?
And can this power be applied to any mechanical purposes?]
XIV. I. "SYLPHS! if with morn destructive Eurus springs,
O, clasp the Harebel with your velvet wings;
525 Screen with thick leaves the Jasmine as it blows,
And shake the white rime from the shuddering Rose;
Whilst Amaryllis turns with graceful ease
Her blushing beauties, and eludes the breeze.--
SYLPHS! if at noon the Fritillary droops,
530 With drops nectareous hang her nodding cups;
Thin clouds of Gossamer in air display,
And hide the vale's chaste Lily from the ray;
Whilst Erythrina o'er her tender flower
Bends all her leaves, and braves the sultry hour;--
535 Shield, when cold Hesper sheds his dewy light,
Mimosa's soft sensations from the night;
Fold her thin foilage, close her timid flowers,
And with ambrosial slumbers guard her bowers;
O'er each warm wall while Cerea flings her arms,
540 And wastes on night's dull eye a blaze of charms.
[Illustration: _Erythrina Corallodendron. London Published Dec'r 1st by
J. Johnson St. Paul's Church Yard._]
[_With ambrosial slumbers_. l. 538. Many vegetables during the night do
not seem to respire, but to sleep like the dormant animals and insects
in winter. This appears from the mimosa and many other plants closing
the upper sides of their leaves together in their sleep, and thus
precluding that side of them from both light and air. And from many
flowers closing up the polished or interior side of their petals, which
we have also endeavoured to shew to be a respiratory organ.
The irritability of plants is abundantly evinced by the absorption and
pulmonary circulation of their juices; their sensibility is shewn by the
approaches of the males to the females, and of the females to the males
in numerous instances; and, as the essential circumstance of sleep
consists in the temporary abolition of voluntary power alone, the sleep
of plants evinces that they possess voluntary power; which also
indisputably appears in many of them by closing their petals or their
leaves during cold, or rain, or darkness, or from mechanic violence.]
2. Round her tall Elm with dewy fingers twine
The gadding tendrils of the adventurous Vine;
From arm to arm in gay festoons suspend
Her fragrant flowers, her graceful foliage bend;
545 Swell with sweet juice her vermil orbs, and feed
Shrined in transparent pulp her pearly seed;
Hang round the Orange all her silver bells,
And guard her fragrance with Hesperian spells;
Bud after bud her polish'd leaves unfold,
550 And load her branches with successive gold.
So the learn'd Alchemist exulting sees
Rise in his bright matrass DIANA'S trees;
Drop after drop, with just delay he pours
The red-fumed acid on Potosi's ores;
555 With sudden flash the fierce bullitions rise,
And wide in air the gas phlogistic flies;
Slow shoot, at length, in many a brilliant mass
Metallic roots across the netted glass;
Branch after branch extend their silver stems,
560 Bud into gold, and blossoms into gems.
[_Diana's trees_, l. 552. The chemists and astronomers from the earliest
antiquity have used the same characters to represent the metals and the
planets, which were most probably outlines or abstracts of the original
hieroglyphic figures of Egypt. These afterwards acquired niches in their
temples, and represented Gods as well as metals and planets; whence
silver is called Diana, or the moon, in the books of alchemy.
The process for making Diana's silver tree is thus described by Lemeri.
Dissolve one ounce of pure silver in acid of nitre very pure and
moderately strong; mix this solution with about twenty ounces of
distilled water; add to this two ounces of mercury, and let it remain at
rest. In about four days there will form upon the mercury a tree of
silver with branches imitating vegetation.
1. As the mercury has a greater affinity than silver with the nitrous
acid, the silver becomes precipitated; and, being deprived of the
nitrous oxygene by the mercury, sinks down in its metallic form and
lustre. 2. The attraction between silver and mercury, which causes them
readily to amalgamate together, occasions the precipitated silver to
adhere to the surface of the mercury in preference to any other part of
the vessel. 3. The attraction of the particles of the precipitated
silver to each other causes the beginning branches to thicken and
elongate into trees and shrubs rooted on the mercury. For other
circumstances concerning this beautiful experiment see Mr. Keir's
Chemical Dictionary, art. Arbor Dianae; a work perhaps of greater
utility to mankind than the lost Alexandrian Library; the continuation
of which is so eagerly expected by all, who are occupied in the arts, or
attached to the sciences.]
So sits enthron'd in vegetable pride
Imperial KEW by Thames's glittering side;
Obedient sails from realms unfurrow'd bring
For her the unnam'd progeny of spring;
565 Attendant Nymphs her dulcet mandates hear,
And nurse in fostering arms the tender year,
Plant the young bulb, inhume the living seed,
Prop the weak stem, the erring tendril lead;
Or fan in glass-built fanes the stranger flowers
570 With milder gales, and steep with warmer showers.
Delighted Thames through tropic umbrage glides,
And flowers antarctic, bending o'er his tides;
Drinks the new tints, the sweets unknown inhales,
And calls the sons of science to his vales.
575 In one bright point admiring Nature eyes
The fruits and foliage of discordant skies,
Twines the gay floret with the fragrant bough,
And bends the wreath round GEORGE'S royal brow.
--Sometimes retiring, from the public weal
580 One tranquil hour the ROYAL PARTNERS steal;
Through glades exotic pass with step sublime,
Or mark the growths of Britain's happier clime;
With beauty blossom'd, and with virtue blaz'd,
Mark the fair Scions, that themselves have rais'd;
585 Sweet blooms the Rose, the towering Oak expands,
The Grace and Guard of Britain's golden lands.
XV. SYLPHS! who, round earth on purple pinions borne,
Attend the radiant chariot of the morn;
Lead the gay hours along the ethereal hight,
590 And on each dun meridian shower the light;
SYLPHS! who from realms of equatorial day
To climes, that shudder in the polar ray,
From zone to zone pursue on shifting wing,
The bright perennial journey of the spring;
595 Bring my rich Balms from Mecca's hallow'd glades,
Sweet flowers, that glitter in Arabia's shades;
Fruits, whose fair forms in bright succession glow
Gilding the Banks of Arno, or of Po;
Each leaf, whose fragrant steam with ruby lip
600 Gay China's nymphs from pictur'd vases sip;
Each spicy rind, which sultry India boasts,
Scenting the night-air round her breezy coasts;
Roots whose bold stems in bleak Siberia blow,
And gem with many a tint the eternal snow;
605 Barks, whose broad umbrage high in ether waves
O'er Ande's steeps, and hides his golden caves;
--And, where yon oak extends his dusky shoots
Wide o'er the rill, that bubbles from his roots;
Beneath whose arms, protected from the storm
610 A turf-built altar rears it's rustic form;
SYLPHS! with religious hands fresh garlands twine,
And deck with lavish pomp HYGEIA'S shrine.
"Call with loud voice the Sisterhood, that dwell
On floating cloud, wide wave, or bubbling well;
615 Stamp with charm'd foot, convoke the alarmed Gnomes
From golden beds, and adamantine domes;
Each from her sphere with beckoning arm invite,
Curl'd with red flame, the Vestal Forms of light.
Close all your spotted wings, in lucid ranks
620 Press with your bending knees the crowded banks,
Cross your meek arms, incline your wreathed brows,
And win the Goddess with unwearied vows.
"Oh, wave, HYGEIA! o'er BRITANNIA'S throne
Thy serpent-wand, and mark it for thy own;
625 Lead round her breezy coasts thy guardian trains,
Her nodding forests, and her waving plains;
Shed o'er her peopled realms thy beamy smile,
And with thy airy temple crown her isle!"
The GODDESS ceased,--and calling from afar
630 The wandering Zephyrs, joins them to her car;
Mounts with light bound, and graceful, as she bends,
Whirls the long lash, the flexile rein extends;
On whispering wheels the silver axle slides,
Climbs into air, and cleaves the crystal tides;
635 Burst from its pearly chains, her amber hair
Streams o'er her ivory shoulders, buoy'd in air;
Swells her white veil, with ruby clasp confined
Round her fair brow, and undulates behind;
The lessening coursers rise in spiral rings,
640 Pierce the slow-sailing clouds, and stretch their shadowy wings.
CONTENTS
OF
THE NOTES.
CANTO I.
Rosicrucian machinery. 73
All bodies are immersed in the matter of heat. Particles of bodies do
not touch each other. 97
Gradual progress of the formation of the earth, and of plants and
animals. Monstrous births 101
Fixed stars approach towards each other, they were projected from chaos
by explosion, and the planets projected from them 105
An atmosphere of inflammable air above the common atmosphere principally
about the poles 123
Twilight fifty miles high. Wants further observations 126
Immediate cause of volcanos from steam and other vapours. They prevent
greater earthquakes 152
Conductors of heat. Cold on the tops of mountains 176
Phosphorescent light in the evening from all bodies 177
Phosphoric light from calcined shells. Bolognian stone. Experiments of
Beccari and Wilson 182
Ignis fatuus doubtful 189
Electric Eel. Its electric organs. Compared to the electric Leyden phial
202
Discovery of fire. Tools of steel. Forests subdued. Quantity of food
increased by cookery 212
Medusa originally an hieroglyphic of divine wisdom 218
Cause of explosions from combined heat. Heat given out from air in
respiration. Oxygene looses less heat when converted into nitrous acid
than in any other of its combinations 226
Sparks from the collision of flints are electric. From the collision of
flint and steel are from the combustion of the steel 229
Gunpowder described by Bacon. Its power. Should be lighted in the
centre. A new kind of it. Levels the weak and strong 242
Steam-engine invented by Savery. Improved by Newcomen. Perfected by Watt
and Boulton 254
Divine benevolence. The parts of nature not of equal excellence 278
Mr. Boulton's steam-engine for the purpose of coining would save many
lives from the executioner 281
Labours of Hercules of great antiquity. Pillars of Hercules. Surface of
the Mediteranean lower than the Atlantic. Abyla and Calpe. Flood of
Deucalion 297
Accumulation of electricity not from friction 335
Mr. Bennet's sensible electrometer 345
Halo of saints is pictorial language 358
We have a sense adapted to perceive heat but not electricity 365
Paralytic limbs move by electric influence 367
Death of Professor Richman by electricity 373
Lightning drawn from the clouds. How to be safe in thunder storms 383
Animal heat from air in respiration. Perpetual necessity of respiration.
Spirit of animation perpetually renewed 401
Cupid rises from the egg of night. Mrs. Cosway's painting of this
subject 413
Western-winds. Their origin. Warmer than south-winds. Produce a thaw
430
Water expands in freezing. Destroys succulent plants, not resinous ones.
Trees in valleys more liable to injury. Fig-trees bent to the ground in
winter 439
Buds and bulbs are the winter cradle of the plant. Defended from frost
and from insects. Tulip produces one flower-bulb and several leaf-bulbs,
and perishes. 460
Matter of heat is different from light. Vegetables blanched by exclusion
of light. Turn the upper surface of their leaves to the light. Water
decomposed as it escapes from their pores. Hence vegetables purify air
in the day time only. 462
Electricity forwards the growth of plants. Silk-worms electrised spin
sooner. Water decomposed in vegetables, and by electricity 463
Sympathetic inks which appear by heat, and disappear in the cold. Made
from cobalt 487
Star in Cassiope's chair 515
Ice-islands 100 fathoms deep. Sea-ice more difficult of solution. Ice
evaporates producing great cold. Ice-islands increase. Should be
navigated into southern climates. Some ice-islands have floated
southwards 60 miles long. Steam attending them in warm climates 529
Monsoon cools the sands of Abyssinia 547
Ascending vapours are electrised plus, as appears from an experiment of
Mr. Bennet. Electricity supports vapour in clouds. Thunder showers from
combination of inflammable and vital airs 553
CANTO II.
Solar volcanos analogous to terrestrial and lunar ones. Spots of the sun
are excavations 14
Spherical form of the earth. Ocean from condensed vapour. Character of
Mr. Whitehurst 17
Granite the oldest part of the earth. Then limestone. And lastly, clay,
iron, coal, sandstone. Three great concentric divisions of the globe
35
Formation of primeval islands before the production of the moon.
Paradise. The Golden Age. Rain-bow. Water of the sea originally fresh
36
Venus rising from the sea an hieroglyphic emblem of the production of
the earth beneath the ocean 47
First great volcanos in the central parts of the earth. From steam,
inflammable gas, and vital air. Present volcanos like mole-hills 68
Moon has little or no atmosphere. Its ocean is frozen. Is not yet
inhabited, but may be in time 82
Earth's axis changed by the ascent of the moon. Its diurnal motion
retarded. One great tide 84
Limestone produced from shells. Spars with double refractions. Marble.
Chalk 93
Antient statues of Hercules. Antinous. Apollo. Venus. Designs of
Roubiliac. Monument of General Wade. Statues of Mrs. Damer 101
Morasses rest on limestone. Of immense extent 116
Salts from animal and vegetable bodies decompose each other, except
marine salt. Salt mines in Poland. Timber does not decay in them. Rock-
salt produced by evaporation from sea-water. Fossil shells in salt
mines. Salt in hollow pyramids. In cubes. Sea-water contains about one-
thirtieth of salt 119
Nitre, native in Bengal and Italy. Nitrous gas combined with vital air
produces red clouds, and the two airs occupy less space than one of them
before, and give out heat. Oxygene and azote produce nitrous acid 143
Iron from decomposed vegetables. Chalybeat springs. Fern-leaves in
nodules of iron. Concentric spheres of iron nodules owing to polarity,
like iron-filings arranged by a magnet. Great strata of the earth owing
to their polarity 183
Hardness of steel for tools. Gave superiority to the European nations.
Welding of steel. Its magnetism. Uses of gold 192
Artificial magnets improved by Savery and Dr. Knight, perfected by Mr.
Michel. How produced. Polarity owing to the earth's rotatory motion. The
electric fluid, and the matter of heat, and magnetism gravitate on each
other. Magnetism being the lightest is found nearest the axis of the
motion. Electricity produces northern lights by its centrifugal motion
193
Acids from vegetable recrements. Flint has its acid from the new world.
Its base in part from the old world, and in part from the new. Precious
stones 215
Diamond. Its great refraction of light. Its volatibility by heat. If an
inflammable body. 228
Fires of the new world from fermentation. Whence sulphur and bitumen by
sublimation, the clay, coal, and flint remaining 275
Colours not distinguishable in the enamel-kiln, till a bit of dry wood
is introduced 283
Etrurian pottery prior to the foundations of Rome. Excelled in fine
forms, and in a non-vitreous encaustic painting, which was lost till
restored by Mr. Wedgwood. Still influences the taste of the inhabitants
291
Mr. Wedgwood's cameo of a slave in chains, and of Hope 315
Basso-relievos of two or more colours not made by the antients. Invented
by Mr. Wedgwood 342
Petroleum and naptha have been sublimed. Whence jet and amber. They
absorb air. Attract straws when rubbed. Electricity from electron the
greek name for amber 353
Clefts in granite rocks in which metals are found. Iron and manganese
found in all vegetables. Manganese in limestone. Warm springs from steam
rising up the clefts of granite and limestone. Ponderous earth in
limestone clefts and in granite. Copper, lead, iron, from descending
materials. High mountains of granite contain no ores near their summits.
Transmutation of metals. Of lead into calamy. Into silver 398
Armies of Cambytes destroyed by famine, and by sand-storms 435
Whirling turrets of sand described and explained 478
Granite shews iron as it decomposes. Marble decomposes. Immense quantity
of charcoal exists in limestone. Volcanic slags decompose, and become
clay 523
Millstones raised by wooden pegs 524
Hannibal made a passage by fire over the Alps 534
Passed tense of many words twofold, as driven or drove, spoken or spoke.
A poetic licence 609
CANTO III.
Clouds consist of aqueous spheres, which do not easily unite, like
globules of quicksilver, as may be seen in riding through water. Owing
to electricity. Snow. Hailstones rounded by attrition and dissolution of
their angles. Not from frozen drops of water 15
Dew on points and edges of grass, or hangs over cabbage-leaves, needle
floats on water 18
Mists over rivers and on mountains. Halo round the moon. Shadow of a
church-steeple upon a mist. Dry mist, or want of transparency of the
air, a sign of fair-weather 20
Tides on both sides of the earth. Moon's tides should be much greater
than the earth's tides. The ocean of the moon is frozen 61
Spiral form of shells saves calcareous matter. Serves them as an organ
of hearing. Calcareous matter produced from inflamed membranes. Colours
of shells, labradore-stone from mother-pearl. Fossil shells not now
found recent 66
Sea-insects like flowers. Actinia 82
Production of pearls, not a disease of the fish. Crab's eyes. Reservoirs
of pearly matter 84
Rocks of coral in the south-sea. Coralloid limestone at Linsel, and
Coalbrook Dale 90
Rocks thrown from mountains, ice from glaciers, and portions of earth,
or morasses, removed by columns of water. Earth-motion in Shropshire.
Water of wells rising above the level of the ground. St. Alkmond's well
near Derby might be raised many yards, so as to serve the town. Well at
Sheerness, and at Hartford in Connecticut 116
Moonsoons attended with rain Overflowing of the Nile. Vortex of
ascending air. Rising of the Dogstar announces the floods of the Nile.
Anubis hung out upon their temples 129
Situations exempt from rain. At the Line in Lower Egypt. On the coast of
Peru 138
Giesar, a boiling fountain in Iceland. Water with great degrees of heat
dissolves siliceous matter. Earthquake from steam 150
Warm springs not from decomposed pyrites. From steam rising up fissures
from great depths 166
Buxton bath possesses 82 degrees of heat. Is improperly called a warm
bath. A chill at immersion, and then a sensation of warmth, like the eye
in an obscure room owing to increased sensibility of the skin 184
Water compounded of pure air and inflammable air with as much matter of
heat as preserves it fluid. Perpetually decomposed by vegetables in the
sun's light, and recomposed in the atmosphere 204
Mythological interpretation of Jupiter and Juno designed as an emblem of
the composition of water from two airs 260
Death of Mrs. French 308
Tomb of Mr. Brindley 341
Invention of the pump. The piston lifts the atmosphere above it. The
surrounding atmosphere presses up the water into the vacuum. Manner in
which a child sucks 366
Air-cell in engines for extinguishing fire. Water dispersed by the
explosion of Gunpowder. Houses preserved from fire by earth on the
floors, by a second ceiling of iron-plates or coarse mortar. Wood
impregnated with alabaster or flint 406
Muscular actions and sensations of plants 460
River Achelous. Horn of Plenty 495
Flooding lands defends them from vernal frosts. Some springs deposit
calcareous earth. Some contain azotic gas, which contributes to produce
nitre. Snow water less serviceable 540
CANTO IV.
Cacalia produces much honey, that a part may be taken by insects without
injury 2
Analysis of common air. Source of azote. Of Oxygene. Water decomposed by
vegetable pores and the sun's light. Blood gives out phlogiston and
receives vital air. Acquires heat and the vivifying principle 34
Cupid and Psyche 48
Simoom, a pestilential wind. Described. Owing to volcanic electricity.
Not a whirlwind 65
Contagion either animal or vegetable 82
Thyrsis escapes the Plague 91
Barometer and air-pump, Dew on exhausting the receiver though the
hygrometer points to dryness. Rare air will dissolve or acquire more
heat, and more moisture, and more electricity 128
Sound propagated best by dense bodies, as wood, and water, and earth.
Fish in spiral shells all ear 164
Discoveries of Dr. Priestley. Green vegetable matter. Pure air contained
in the calces of metals, as minium, manganese, calamy, ochre 166
Fable of Proserpine an antient chemical emblem 178
Diving balloons supplied with pure air from minium. Account of one by
Mr. Boyle 195
Mr. Day. Mr. Spalding 217
Captain Pierce and his daughters 219
Pestilential winds of volcanic origin. Jordan flows through a country of
volcanos 294
Change of wind owing to small causes. If the wind could be governed, the
products of the earth would be doubled, and its number of inhabitants
increased 308
Mr. Kirwan's treatise on temperature of climates 342
Seeds of plants. Spawn of fish. Nutriment lodged in seeds. Their
preservation in their seed-vessels 355
Fixed stars approach each other 369
Fable of the Phoenix 377
Plants visible within bulbs, and buds, and seeds 383
Great Egg of Night 406
Seeds shoot into the ground. Pith. Seed-lobes. Starch converted into
sugar. Like animal chyle 411
Light occasions the actions of vegetable muscles. Keeps them awake
422
Vegetable love in Parnassia, Nigella. Vegetable adultery in Collinsonia
456
Strong vegetable shoots and roots bound with wire, in part debarked,
whence leaf-buds converted into flower-buds. Theory of this curious fact
463
Branches bent to the horizon bear more fruit 466
Engrafting of a spotted passion-flower produced spots upon the stock.
Apple soft on one side and hard on the other 483
Cyprepedium assumes the form of a large spider to affright the humming-
bird. Fly-ophris. Willow-wren sucks the honey of the crown-imperial
505
Diseases of plants four kinds. Honey-dew 511
Ergot a disease of rye 513
Glass unannealed. Its cracks owing to elasticity. One kind of lead-ore
cracks into pieces. Prince Rupert's drops. Elastic balls 519
Sleep of plants. Their irritability, sensibility, and voluntary motions
538
ADDITIONAL NOTES.
NOTE I.--METEORS.
_Etherial Forms! you chase the shooting stars,
Or yoke the vollied lightnings to your cars._
CANTO I. l. 115.
There seem to be three concentric strata of our incumbent atmosphere; in
which, or between them, are produced four kinds of meteors; lightning,
shooting stars, fire-balls, and northern lights. First, the lower region
of air, or that which is dense enough to resist by the adhesion of its
particles the descent of condensed vapour, or clouds, which may extend
from one to three or four miles high. In this region the common
lightning is produced from the accumulation or defect of electric matter
in those floating fields of vapour either in respect to each other, or
in respect to the earth beneath them, or the dissolved vapour above
them, which is constantly varying both with the change of the form of
the clouds, which thus evolve a greater or less surface; and also with
their ever-changing degree of condensation. As the lightning is thus
produced in dense air, it proceeds but a short course on account of the
greater resistance which it encounters, is attended with a loud
explosion, and appears with a red light.
2. The second region of the atmosphere I suppose to be that which has
too little tenacity to support condensed vapour or clouds; but which yet
contains invisible vapour, or water in aerial solution. This aerial
solution of water differs from that dissolved in the matter of heat, as
it is supported by its adhesion to the particles of air, and is not
precipitated by cold. In this stratum it seems probable that the meteors
called shooting stars are produced; and that they consist of electric
sparks, or lightning, passing from one region to another of these
invisible fields of aero-aqueous solution. The height of these shooting
stars has not yet been ascertained by sufficient observation; Dr.
Blagden thinks their situation is lower down in the atmosphere than that
of fireballs, which he conjectures from their swift apparent motion, and
ascribes their smallness to the more minute division of the electric
matter of which they are supposed to consist, owing to the greater
resistance of the denser medium through which they pass, than that in
which the fire-balls exist. Mr. Brydone observed that the shooting stars
appeared to him to be as high in the atmosphere, when he was near the
summit of mount Etna, as they do when observed from the plain. Phil.
Tran. Vol. LXIII.
As the stratum of air, in which shooting stars are supposed to exist is
much rarer than that in which lightning resides, and yet much denser
than that in which fire-balls are produced, they will be attracted at a
greater distance than the former, and at a less than the latter. From
this rarity of the air so small a sound will be produced by their
explosion, as not to reach the lower parts of the atmosphere; their
quantity of light from their greater distance being small, is never seen
through dense air at all, and thence does not appear red, like lightning
or fire balls. There are no apparent clouds to emit or to attract them,
because the constituent parts of these aero-aqueous regions may possess
an abundance or deficiency of electric matter and yet be in perfect
reciprocal solution. And lastly their apparent train of light is
probably owing only to a continuance of their impression on the eye; as
when a fire-stick is whirled in the dark it gives the appearance of a
compleat circle of fire: for these white trains of shooting stars
quickly vanish, and do not seem to set any thing on fire in their
passage, as seems to happen in the transit of fire-balls.
3. The second region or stratum of air terminates I suppose where the
twilight ceases to be refracted, that is, where the air is 3000 times
rarer than at the surface of the earth; and where it seems probable that
the common air ends, and is surrounded by an atmosphere of inflammable
gas tenfold rarer than itself. In this region I believe fire-balls
sometimes to pass, and at other times the northern lights to exist. One
of these fire-balls or draco volans, was observed by Dr. Pringle and
many others on Nov. 26, 1758, which was afterwards estimated to have
been a mile and a half in circumference, to have been about one hundred
miles high, and to have moved towards the north with a velocity of near
thirty miles in a second of time. This meteor had a real tail many miles
long, which threw off sparks in its course, and the whole exploded with
a sound like distant thunder. Philos. Trans. Vol. LI.
Dr. Blagden has related the history of another large meteor, or fire-
ball, which was seen the 18th of August, 1783, with many ingenious
observations and conjectures. This was estimated to be between 60 and 70
miles high, and to travel 1000 miles at the rate of about twenty miles
in a second. This fire-ball had likewise a real train of light left
behind it in its passage, which varied in colour; and in some part of
its course gave off sparks or explosions where it had been brightest;
and a dusky red streak remained visible perhaps a minute. Philos. Trans.
Vol. LXXIV.
These fire-balls differ from lightning, and from shooting stars in many
remarkable circumstances; as their very great bulk, being a mile and a
half in diameter; their travelling 1000 miles nearly horizontally; their
throwing off sparks in their passage; and changing colours from bright
blue to dusky red; and leaving a train of fire behind them, continuing
about a minute. They differ from the northern lights in not being
diffused, but passing from one point of the heavens to another in a
defined line; and this in a region above the crepuscular atmosphere,
where the air is 3000 tines rarer than at the surface of the earth.
There has not yet been even a conjecture which can account for these
appearances!--One I shall therefore hazard; which, if it does not
inform, may amuse the reader.
In the note on l. 123, it was shewn that there is probably a supernatant
stratum of inflammable gas or hydrogene, over the common atmosphere; and
whose density at the surface where they meet, must be at least ten times
less than that upon which it swims; like chemical ether floating upon
water, and perhaps without any real contact. 1. In this region, where
the aerial atmosphere terminates and the inflammable one begins, the
quantity of tenacity or resistance must be almost inconceivable; in
which a ball of electricity might pass 1000 miles with greater ease than
through a thousandth part of an inch of glass. 2. Such a ball of
electricity passing between inflammable and common air would set fire to
them in a line as it patted along; which would differ in colour
according to the greater proportionate commixture of the two airs; and
from the same cause there might occur greater degrees of inflammation,
or branches of fire, in some parts of its course.
As these fire-balls travel in a defined line, it is pretty evident from
the known laws of electricity, that they must be attracted; and as they
are a mile or more in diameter, they must be emitted from a large
surface of electric matter; because large nobs give larger sparks, less
diffused, and more brightly luminous, than less ones or points, and
resist more forceably the emission of the electric matter. What is there
in nature can attract them at so great a distance as 1000 miles, and so
forceably as to detach an electric spark of a mile diameter? Can
volcanos at the time of their eruptions have this effect, as they are
generally attended with lightning? Future observations must discover
these secret operations of nature! As a stream of common air is carried
along with the passage of electric aura from one body to another; it is
easy to conceive, that the common air and the inflammable air between
which the fire-ball is supposed to pass, will be partially intermixed by
being thus agitated, and so far as it becomes intermixed it will take
fire, and produce the linear flame and branching sparks above described.
In this circumstance of their being attracted, and thence passing in a
defined line, the fire-balls seem to differ from the coruscations of the
aurora borealis, or northern lights, which probably take place in the
same region of the atmosphere; where the common air exists in extreme
tenuity, and is covered by a still rarer sphere of inflammable gas, ten
times lighter than itself.
As the electric streams, which constitute these northern lights, seem to
be repelled or radiated from an accumulation of that fluid in the north,
and not attracted like the fireballs; this accounts for the diffusion of
their light, as well as the silence of their passage; while their
variety of colours, and the permanency of them, and even the breadth of
them in different places, may depend on their setting on fire the
mixture of inflammable and common air through which they pass; as seems
to happen in the transit of the fire-balls.
It was observed by Dr. Priestley that the electric shock taken through
inflammable air was red, in common air it is blueish; to these
circumstances perhaps some of the colours of the northern lights may
bear analogy; though the density of the medium through which light is
seen must principally vary its colour, as is well explained by Mr.
Morgan. Phil. Trans. Vol. LXXV. Hence lightning is red when seen through
a dark cloud, or near the horizon; because the more refrangible rays
cannot permeate so dense a medium. But the shooting stars consist of
white light, as they are generally seen on clear nights, and nearly
vertical: in other situations their light is probably too faint to come
to us. But as in some remarkable appearances of the northern lights, as
in March, 1716, all the prismatic colours were seen quickly to succeed
each other, these appear to have been owing to real combustion; as the
density of the interposed medium could not be supposed to change so
frequently; and therefore these colours must have been owing to
different degrees of heat according to Mr. Morgan's theory of
combustion. In Smith's Optics, p. 69. the prismatic colours, and optical
deceptions of the northern lights are described by Mr. Cotes.
The Torricellian vacuum, if perfectly free from air, is said by Mr.
Morgan and others to be a perfect non-conductor. This circumstance
therefore would preclude the electric streams from rising above the
atmosphere. But as Mr. Morgan did not try to pass an electric shock
through a vacuum, and as air, or something containing air, surrounding
the transit of electricity may be necessary to the production of light,
the conclusion may perhaps still be dubious. If however the streams of
the northern lights were supposed to rise above our atmosphere, they
would only be visible at each extremity of their course; where they
emerge from, or are again immerged into the atmosphere; but not in their
journey through the vacuum; for the absence of electric light in a
vacuum is sufficiently proved by the common experiment of shaking a
barometer in the dark; the electricity, produced by the friction of the
mercury in the glass at its top, is luminous if the barometer has a
little air in it; but there is no light if the vacuum be complete.
The aurora borealis, or northern dawn, is very ingeniously accounted for
by Dr. Franklin on principles of electricity. He premises the following
electric phenomena: 1. that all new fallen snow has much positive
electricity standing on its surface. 2. That about twelve degrees of
latitude round the poles are covered with a crust of eternal ice, which
is impervious to the electric fluid. 3. That the dense part of the
atmosphere rises but a few miles high; and that in the rarer parts of it
the electric fluid will pass to almost any distance.
Hence he supposes there must be a great accumulation of positive
electric matter on the fresh fallen snow in the polar regions; which,
not being able to pass through the crust of ice into the earth, must
rise into the rare air of the upper parts of our atmosphere, which will
the least resist its passage; and passing towards the equator descend
again into the denser atmosphere, and thence into the earth in silent
streams. And that many of the appearances attending these lights are
optical deceptions, owing to the situation of the eye that beholds them;
which makes all ascending parallel lines appear to converge to a point.
The idea, above explained in note on l. 123, of the existence of a
sphere of inflammable gas over the aerial atmosphere would much favour
this theory of Dr. Franklin; because in that case the dense aerial
atmosphere would rise a much less height in the polar regions,
diminishing almost to nothing at the pole itself; and thus give an
easier passage to the ascent of the electric fluid. And from the great
difference in the specific gravity of the two airs, and the velocity of
the earth's rotation, there must be a place between the poles and the
equator, where the superior atmosphere of inflammable gas would
terminate; which would account for these streams of the aurora borealis
not appearing near the equator; add to this that it is probable the
electric fluid may be heavier than the magnetic one; and will thence by
the rotation of the earth's surface ascend over the magnetic one by its
centrifugal force; and may thus be induced to rise through the thin
stratum of aerial atmosphere over the poles. See note on Canto II. l.
193. I shall have occasion again to mention this great accumulation of
inflammable air over the poles; and to conjecture that these northern
lights may be produced by the union of inflammable with common air,
without the assistance of the electric spark to throw them into
combustion.
The antiquity of the appearance of northern lights has been doubted; as
none were recorded in our annals since the remarkable one on Nov. 14,
1574, till another remarkable one on March 6, 1716, and the three
following nights, which were seen at the same time in Ireland, Russia,
and Poland, extending near 30 degrees of longitude and from about the
50th degree of latitude over almost all the north of Europe. There is
however reason to believe them of remote antiquity though inaccurately
described; thus the following curious passage from the Book of
Maccabees, (B. II. c. v.) is such a description of them, as might
probably be given by an ignorant and alarmed people. "Through all the
city, for the space of almost forty days, there were seen horsemen
running in the air, in cloth of gold, and armed with lances, like a band
of soldiers; and troops of horsemen in array encountering and running
one against another, with shaking of shields and multitude of pikes, and
drawing of swords, and casting of darts, and glittering of golden
ornaments and harness."
NOTE II.--PRIMARY COLOURS.
_Cling round the aerial bow with prisms bright,
And pleased untwist the sevenfold threads of light._
CANTO I. l. 117.
The manner in which the rainbow is produced was in some measure
understood before Sir Isaac Newton had discovered his theory of colours.
The first person who expressly shewed the rainbow to be formed by the
reflection of the sunbeams from drops of falling rain was Antonio de
Dominis. This was afterwards more fully and distinctly explained by Des
Cartes. But what caused the diversity of its colours was not then
understood; it was reserved for the immortal Newton to discover that the
rays of light consisted of seven combined colours of different
refrangibility, which could be seperated at pleasure by a wedge of
glass. Pemberton's View of Newton.
Sir Isaac Newton discovered that the prismatic spectrum was composed of
seven colours in the following proportions, violet 80, indigo 40, blue
60, green 60, yellow 48, orange 27, red 45. If all these colours be
painted on a circular card in the proportions above mentioned, and the
card be rapidly whirled on its center, they produce in the eye the
sensation of white. And any one of these colours may be imitated by
painting a card with the two colours which are contiguous to it, in the
same proportions as in the spectrum, and whirling them in the same
manner. My ingenious friend, Mr. Galton of Birmingham, ascertained in
this manner by a set of experiments the following propositions; the
truth of which he had preconceived from the above data.
1. Any colour in the prismatic spectrum may be imitated by a mixture of
the two colours contiguous to it.
2. If any three successive colours in the prismatic spectrum are mixed,
they compose only the second or middlemost colour.
3. If any four succesive colours in the prismatic spectrum be mixed, a
tint similar to a mixture of the second and third colours will be
produced, but not precisely the same, because they are not in the same
proportion.
4. If beginning with any colour in the circular spectrum, you take of
the second colour a quantity equal to the first, second, and third; and
add to that the fifth colour, equal in quantity to the fourth, fifth,
and sixth; and with these combine the seventh colour in the proportion
it exists in the spectrum, white will be produced. Because the first,
second, and third, compose only the second; and the fourth, fifth, and
sixth, compose only the fifth; therefore if the seventh be added, the
same effect is produced, as if all the seven were employed.
5. Beginning with any colour in the circular spectrum, if you take a
tint composed of a certain proportion of the second and third, (equal in
quantity to the first, second, third, and fourth,) and add to this the
sixth colour equal in quantity to the fifth, sixth, and seventh, white
will be produced.
From these curious experiments of Mr. Galton many phenomena in the
chemical changes of colours may probably become better understood;
especially if, as I suppose, the same theory must apply to transmitted
colours, as to reflected ones. Thus it is well known, that if the glass
of mangonese, which is a tint probably composed of violet and indigo, be
mixed in a certain proportion with the glass of lead, which is yellow;
that the mixture becomes transparent. Now from Mr. Galton's experiments
it appears, that in reflected colours such a mixture would produce
white, that is, the same as if all the colours were reflected. And
therefore in transmitted colours the same circumstances must produce
transparency, that is, the same as if all the colours were transmitted.
For the particles, which constitute the glass of mangonese will transmit
red, violet, indigo, and blue; and those of the glass of lead will
transmit orange, yellow, and green; hence all the primary colours by a
mixture of these glasses become transmitted, that is, the glass becomes
transparent.
Mr. Galton has further observed that five successive prismatic colours
may be combined in such proportions as to produce but one colour, a
circumstance which might be of consequence in the art of painting. For
if you begin at any part of the circular spectrum above described, and
take the first, second, and third colours in the proportions in which
they exist in the spectrum; these will compose only the second colour
equal in quantity to the first, second, and third; add to these the
third, fourth, and fifth in the proportion they exist in the spectrum,
and these will produce the fourth colour equal in quantity to the third,
fourth, and fifth. Consequently this is precisely the same thing, as
mixing the second and fourth colours only; which mixture would only
produce the third colour. Therefore if you combine the first, second,
fourth, and fifth in the proportions in which they exist in the
spectrum, with double the quantity of the third colour, this third
colour will be produced. It is probable that many of the unexpected
changes in mixing colours on a painter's easle, as well as in more fluid
chemical mixtures, may depend on these principles rather than on a new
arrangement or combination of their minute particles.
Mr. Galton further observes, that white may universally be produced by
the combination of one prismatic colour, and a tint intermediate to two
others. Which tint may be distinguished by a name compounded of the two
colours, to which it is intermediate. Thus white is produced by a
mixture of red with blue-green. Of orange with indigo-blue. Of Yellow
with violet-indigo. Of green with red-violet. Of blue with Orange-red.
Of indigo with yellow-orange. Of violet with green-yellow. Which he
further remarks exactly coincides with the theory and facts mentioned by
Dr. Robert Darwin of Shrewsbury in his account of ocular spectra; who
has shewn that when one of these contrasted colours has been long
viewed, a spectrum or appearance of the other becomes visible in the
fatigued eye. Philos. Trans. Vol. LXXVI. for the year 1786.
These experiments of Mr. Galton might much assist the copper-plate
printers of callicoes and papers in colours; as three colours or more
might be produced by two copper-plates. Thus suppose some yellow figures
were put on by the first plate, and upon some parts of these yellow
figures and on other parts of the ground blue was laid on by another
copper-plate. The three colours of yellow, blue, and green might be
produced; as green leaves with yellow and blue flowers.
NOTE III.--COLOURED CLOUDS.
_Eve's silken couch with gorgeous tints adorn,
Or fire the arrowy throne of rising morn._
CANTO I. l. 119.
The rays from the rising and setting sun are refracted by our spherical
atmosphere, hence the most refrangible rays, as the violet, indigo, and
blue are reflected in greater quantities from the morning and evening
skies; and the least refrangible ones, as red and orange, are last seen
about the setting sun. Hence Mr. Beguelin observed that the shadow of
his finger on his pocket-book was much bluer in the morning and evening,
when the shadow was about eight times as long as the body from which it
was projected. Mr. Melville observes, that the blue rays being more
refrangible are bent down in the evenings by our atmosphere, while the
red and orange being less refrangible continue to pass on and tinge the
morning and evening clouds with their colours. See Priestley's History
of Light and Colours, p. 440. But as the particles of air, like those of
water, are themselves blue, a blue shadow may be seen at all times of
the day, though much more beautifully in the mornings and evenings, or
by means of a candle in the middle of the day. For if a shadow on a
piece of white paper is produced by placing your finger between the
paper and a candle in the day light, the shadow will appear very blue;
the yellow light of the candle upon the other parts of the paper
apparently deepens the blue by its contrast; these colours being
opposite to each other, as explained in note II.
Colours are produced from clouds or mists by refraction, as well as by
reflection. In riding in the night over an unequal country I observed a
very beautiful coloured halo round the moon, whenever I was covered with
a few feet of mist, as I ascended from the vallies; which ceased to
appear when I rose above the mist. This I suppose was owing to the
thinness of the stratum of mist, in which I was immersed; had it been
thicker, the colours refracted by the small drops, of which a fog
consists, would not have passed through it down to my eye.
There is a bright spot seen on the cornea of the eye, when we face a
window, which is much attended to by portrait painters; this is the
light reflected from the spherical surface of the polished cornea, and
brought to a focus; if the observer is placed in this focus, he sees the
image of the window; if he is placed before or behind the focus, he only
sees a luminous spot, which is more luminous and of less extent, the
nearer he approaches to the focus. The luminous appearance of the eyes
of animals in the dusky corners of a room, or in holes in the earth, may
arise in some instances from the same principle; viz. the reflection of
the light from the spherical cornea; which will be coloured red or blue
in some degree by the morning, evening, or meridian light; or by the
objects from which that light is previously reflected. In the cavern at
Colebrook Dale, where the mineral tar exsudes, the eyes of the horse,
which was drawing a cart from within towards the mouth of it, appeared
like two balls of phosphorus, when he was above 100 yards off, and for a
long time before any other part of the animal was visible. In this case
I suspect the luminous appearance to have been owing to the light, which
had entered the eye, being reflected from the back surface of the
vitreous humour, and thence emerging again in parallel rays from the
animals eye, as it does from the back surface of the drops of the
rainbow, and from the water-drops which lie, perhaps without contact, on
cabbage-leaves, and have the brilliancy of quicksilver. This accounts
for this luminous appearance being best seen in those animals which have
large apertures in their iris, as in cats and horses, and is the only
part visible in obscure places, because this is a better reflecting
surface than any other part of the animal. If any of these emergent rays
from the animals eye can be supposed to have been reflected from the
choroid coat through the semi-transparent retina, this would account for
the coloured glare of the eyes of dogs or cats and rabits in dark
corners.
NOTE IV.--COMETS.
_Alarm with comet-blaze the sapphire plain,
The wan stars glimmering through its silver train._
CANTO I. l. 133.
There have been many theories invented to account for the tails of
comets. Sir Isaac Newton thinks that they consist of rare vapours raised
from the nucleus of the comet, and so rarefied by the sun's heat as to
have their general gravitation diminished, and that they in consequence
ascend opposite to the sun, and from thence reflect the rays of light.
Dr. Halley compares the light of the tails of comets to the streams of
the aurora borealis, and other electric effluvia. Philos. Trans. No.
347.
Dr. Hamilton observes that the light of small stars are seen
undiminished through both the light of the tails of comets, and of the
aurora borealis, and has further illustrated their electric analogy, and
adds that the tails of comets consist of a lucid self-shining substance
which has not the power of refracting or reflecting the rays of light.
Essays.
The tail of the comet of 1744 at one time appeared to extend above 16
degrees from its body, and must have thence been above twenty three
millions of miles long. And the comet of 1680, according to the
calculations of Dr. Halley on November the 11th, was not above one semi-
diameter of the earth, or less than 4000 miles to the northward of the
way of the earth; at which time had the earth been in that part of its
orbit, what might have been the consequence! no one would probably have
survived to have registered the tremendous effects.
The comet of 1531, 1607, and 1682 having returned in the year 1759,
according to Dr. Halley's prediction in the Philos. Trans. for 1705,
there seems no reason to doubt that all the other comets will return
after their proper periods. Astronomers have in general acquiesced in
the conjecture of Dr. Halley, that the comets of 1532, and 1661 are one
and the same comet, from the similarity of the elements of their orbits,
and were therefore induced to expect its return to its perihelium 1789.
As this comet is liable to be disturbed in its ascent from the sun by
the planets Jupiter and Saturn, Dr. Maskelyne expected its return to its
perihelium in the beginning of the year 1789, or the latter end of the
year 1788, and certainly sometime before the 27th of April, 1789, which
prediction has not been fulfilled. Phil. Trans. Vol. LXXVI.
NOTE V.--SUN'S RAYS.
_Or give the sun's phlogistic orb to roll._
CANTO I. l. 136.
The dispute among philosophers about phlogiston is not concerning the
existence of an inflammable principle, but rather whether there be one
or more inflammable principles. The disciples of Stahl, which till
lately included the whole chemical world, believed in the identity of
phlogiston in all bodies which would flame or calcine. The disciples of
Lavoisier pay homage to a plurality of phlogistons under the various
names of charcoal, sulphur, metals, &c. Whatever will unite with _pure_
air, and thence compose an acid, is esteemed in this ingenious theory to
be a different kind of phlogistic or inflammable body. At the same time
there remains a doubt whether these inflammable bodies, as metals,
sulphur, charcoal, &c. may not be compounded of the same phlogiston
along with some other material yet undiscovered, and thus an unity of
phlogiston exist, as in the theory of Stahl, though very differently
applied in the explication of chemical phenomena.
Some modern philosophers are of opinion that the sun is the great
fountain from which the earth and other planets derive all the
phlogiston which they possess; and that this is formed by the
combination of the solar rays with all opake bodies, but particularly
with the leaves of vegetables, which they suppose to be organs adapted
to absorb them. And that as animals receive their nourishment from
vegetables they also obtain in a secondary manner their phlogiston from
the sun. And lastly as great masses of the mineral kingdom, which have
been found in the thin crust of the earth which human labour has
penetrated, have evidently been formed from the recrements of animal and
vegetable bodies, these also are supposed thus to have derived their
phlogiston from the sun.
Another opinion concerning the sun's rays is, that they are not luminous
till they arrive at our atmosphere; and that there uniting with some
part of the air they produce combustion, and light is emitted, and that
an etherial acid, yet undiscovered, is formed from this combustion.
The more probable opinion is perhaps, that the sun is a phlogistic mass
of matter, whose surface is in a state of combustion, which like other
burning bodies emits light with immense velocity in all directions; that
these rays of light act upon all opake bodies, and combining with them
either displace or produce their elementary heat, and become chemically
combined with the phlogistic part of them; for light is given out when
phlogistic bodies unite with the oxygenous principle of the air, as in
combustion, or in the reduction of metallic calxes; thus in presenting
to the flame of a candle a letter-wafer, (if it be coloured with red-
lead,) at the time the red-lead becomes a metallic drop, a flash of
light is perceived. Dr. Alexander Wilson very ingeniously endeavours to
prove that the sun is only in a state of combustion on its surface, and
that the dark spots seen on the disk are excavations or caverns through
the luminous crust, some of which are 4000 miles in diameter. Phil.
Trans. 1774. Of this I shall have occasion to speak again.
NOTE VI.--CENTRAL FIRES.
_Round her still centre tread the burning soil,
And watch the billowy Lavas, as they boil._
CANTO I. l. 139.
M. de Mairan in a paper published in the Histoire de l'Academie de
Sciences, 1765, has endeavoured to shew that the earth receives but a
small part of the heat which it possesses, from the sun's rays, but is
principally heated by fires within itself. He thinks the sun is the
cause of the vicissitudes of our seasons of summer and winter by a very
small quantity of heat in addition to that already residing in the
earth, which by emanations from the centre to the circumference renders
the surface habitable, and without which, though the sun was constantly
to illuminate two thirds of the globe at once, with a heat equal to that
at the equator, it would soon become a mass of solid ice. His reasonings
and calculations on this subject are too long and too intricate to be
inserted here, but are equally curious and ingenious and carry much
conviction along with them.
The opinion that the center of the earth consists of a large mass of
burning lava, has been espoused by Boyle, Boerhave, and many other
philosophers. Some of whom considering its supposed effects on
vegetation and the formation of minerals have called it a second sun.
There are many arguments in support of this opinion, 1. Because the
power of the sun does not extend much beyond ten feet deep into the
earth, all below being in winter and summer always of the same degree of
heat, viz. 48, which being much warmer than the mildest frost, is
supposed to be sustained by some internal distant fire. Add to this
however that from experiments made some years ago by Dr. Franklin the
spring-water at Philadelphia appeared to be of 52° of heat, which seems
further to confirm this opinion, since the climates in North America are
supposed to be colder than those of Europe under similar degrees of
latitude. 2. Mr. De Luc in going 1359 feet perpendicular into the mines
of Hartz on July the 5th, 1778, on a very fine day found the air at the
bottom a little warmer than at the top of the shaft. Phil. Trans. Vol.
LXIX. p. 488. In the mines in Hungary, which are 500 cubits deep, the
heat becomes very troublesome when the miners get below 480 feet depth.
_Morinus de Locis subter_. p. 131. But as some other deep mines as
mentioned by Mr. Kirwan are said to possess but the common heat of the
earth; and as the crust of the globe thus penetrated by human labour is
so thin compared with the whole, no certain deduction can be made from
these facts on either side of the question. 3. The warm-springs in many
parts of the earth at great distance from any Volcanos seem to originate
from the condensation of vapours arising from water which is boiled by
subterraneous fires, and cooled again in their passage through a certain
length of the colder soil; for the theory of chemical solution will not
explain the equality of their heat at all seasons and through so many
centuries. See note on Fucus in Vol. II. See a letter on this subject in
Mr. Pilkinton's View of Derbyshire from Dr. Darwin. 4. From the
situations of volcanos which are always found upon the summit of the
highest mountains. For as these mountains have been lifted up and lose
several of their uppermost strata as they rise, the lowest strata of the
earth yet known appear at the tops of the highest hills; and the beds of
the Volcanos upon these hills must in consequence belong to the lowest
strata of the earth, consisting perhaps of granite or basaltes, which
were produced before the existance of animal or vegetable bodies, and
might constitute the original nucleus of the earth, which I have
supposed to have been projected from the sun, hence the volcanos
themselves appear to be spiracula or chimneys belonging to great central
fires. It is probably owing to the escape of the elastic vapours from
these spiracula that the modern earthquakes are of such small extent
compared with those of remote antiquity, of which the vestiges remain
all over the globe. 5. The great size and height of the continents, and
the great size and depth of the South-sea, Atlantic, and other oceans,
evince that the first earthquakes, which produced these immense changes
in the globe, must have been occasioned by central fires. 6. The very
distant and expeditious communication of the shocks of some great
earthquakes. The earthquake at Lisbon in 1755 was perceived in Scotland,
in the Peak of Derbyshire, and in many other distant parts of Europe.
The percussions of it travelled with about the velocity of sound, viz.
about thirteen miles in a minute. The earthquake in 1693 extended 2600
leagues. (Goldsmith's History.) These phenomena are easily explained if
the central parts of the earth consist of a fluid lava, as a percussion
on one part of such a fluid mass would be felt on other parts of its
confining vault, like a stroke on a fluid contained in a bladder, which
however gentle on one side is perceptible to the hand placed on the
other; and the velocity with which such a concussion would travel would
be that of sound, or thirteen miles in a minute. For further information
on this part of the subject the reader is referred to Mr. Michell's
excellent Treatise on Earthquakes in the Philos. Trans. Vol. LI. 7. That
there is a cavity at the center of the earth is made probable by the
late experiments on the attraction of mountains by Mr. Maskerlyne, who
supposed from other considerations that the density of the earth near
the surface should be five times less than its mean density. Phil.
Trans. Vol. LXV. p. 498. But found from the attraction of the mountain
Schehallien, that it is probable, the mean density of the earth is but
double that of the hill. Ibid. p. 532. Hence if the first supposition be
well founded there would appear to be a cavity at the centre of
considerable magnitude, from whence the immense beds and mountains of
lava, toadstone, basaltes, granite, &c. have been protruded. 8. The
variation of the compass can only be accounted for by supposing the
central parts of the earth to consist of a fluid mass, and that part of
this fluid is iron, which requiring a greater degree of heat to bring it
into fusion than glass or other metals, remains a solid, and the vis
inertiae of this fluid mass with the iron in it, occasions it to perform
fewer revolutions than the crust of solid earth over it, and thus it is
gradually left behind, and the place where the floating iron resides is
pointed to by the direct or retrograde motions of the magnetic needle.
This seems to have been nearly the opinion of Dr. Halley and Mr. Euler.
NOTE VII.--ELEMENTARY HEAT.
_Or sphere on sphere in widening waves expand,
And glad with genial warmth the incumbent land._
CANTO I. l. 143.
A certain quantity of heat seems to be combined with all bodies besides
the sensible quantity which gravitates like the electric fluid amongst
them. This combined heat or latent heat of Dr. Black, when set at
liberty by fermentation, inflammation, crystallization, freezing, or
other chemical attractions producing new _combinations_, passes as a
fluid element into the surrounding bodies. And by thawing, diffusion of
neutral salts in water, melting, and other chemical _solutions_, a
portion of heat is attracted from the bodies in vicinity and enters into
or becomes combined with the new solutions.
Hence a _combination_ of metals with acids, of essential oils and acids,
of alcohol and water, of acids and water, give out heat; whilst a
_solution_ of snow in water or in acids, and of neutral salts in water,
attract heat from the surrounding bodies. So the acid of nitre mixed
with oil of cloves unites with it and produces a most violent flame; the
same acid of nitre poured on snow instantly dissolves it and produces
the greatest degree of cold yet known, by which at Petersburgh
quicksilver was first frozen in 1760.
Water may be cooled below 32º without being frozen, if it be placed on a
solid floor and secured from agitation, but when thus cooled below the
freezing point the least agitation turns part of it suddenly into ice,
and when this sudden freezing takes place a thermometer placed in it
instantly rises as some heat is given out in the act of congelation, and
the ice is thus left with the same _sensible_ degree of cold as the
water had possessed before it was agitated, but is nevertheless now
combined with less _latent_ heat.
A cubic inch of water thus cooled down to 32° mixed with an equal
quantity of boiling water at 212° will cool it to the middle number
between these two, or to 122. But a cubic inch of ice whose sensible
cold also is but 32, mixed with an equal quantity of boiling water, will
cool it six times as much as the cubic inch of cold water
above-mentioned, as the ice not only gains its share of the sensible or
gravitating heat of the boiling water but attracts to itself also and
combines with the quantity of latent heat which it had lost at the time
of its congelation.
So boiling water will acquire but 212° of heat under the common pressure
of the atmosphere, but the steam raised from it by its expansion or by
its solution in the atmosphere combines with and carries away a
prodigious quantity of heat which it again parts with on its
condensation; as is seen in common distillation where the large quantity
of water in the worm-tub is so soon heated. Hence the evaporation of
ether on a thermometer soon sinks the mercury below freezing, and hence
a warmth of the air in winter frequently succeeds a shower.
When the matter of heat or calorique is set at liberty from its
combinations, as by inflammation, it passes into the surrounding bodies,
which possess different capacities of acquiring their share of the loose
or sensible heat; thus a pint measure of cold water at 48° mixed with a
pint of boiling water at 212° will cool it to the degree between these
two numbers, or to 154°, but it requires two pint measures of
quicksilver at 48° of heat to cool one pint of water as above. These and
other curious experiments are adduced by Dr. Black to evince the
existance of combined or latent heat in bodies, as has been explained by
some of his pupils, and well illustrated by Dr. Crawford. The world has
long been in expectation of an account of his discoveries on this
subject by the celebrated author himself.
As this doctrine of elementary heat in its fluid and combined state is
not yet universally received, I shall here add two arguments in support
of it drawn from different sources, viz. from the heat given out or
absorbed by the mechanical condensation or expansion of the air, and
perhaps of other bodies, and from the analogy of the various phenomena
of heat with those of electricity.
I. If a thermometer be placed in the receiver of an air-pump, and the
air hastily exhausted, the thermometer will sink some degrees, and the
glass become steamy; the same occurs in hastily admitting a part of the
air again. This I suppose to be produced by the expansion of part of the
air, both during the exhaustion and re-admission of it; and that the air
so expanded becomes capable of attracting from the bodies in its
vicinity a part of their heat, hence the vapours contained in it and the
glass receiver are for a time colder and the steam is precipitated. That
the air thus parts with its moisture from the cold occasioned by its
rarefaction and not simply by the rarefaction itself is evident, because
in a minute or two the same rarefied air will again take up the dew
deposited on the receiver; and because water will evaporate sooner in
rare than in dense air.
There is a curious phenomenon similar to this observed in the fountain
of Hiero constructed on a large scale at the Chemnicensian mines in
Hungary. In this machine the air in a large vessel is compressed by a
column of water 260 feet high, a stop-cock is then opened, and as the
air issues out with great vehemence, and thus becomes immediately
greatly expanded, so much cold is produced that the moisture from this
stream of air is precipitated in the form of snow, and ice is formed
adhering to the nosel of the cock. This remarkable circumstance is
described at large with a plate of the machine in Philos. Trans. Vol.
LII. for 1761.
The following experiment is related by Dr. Darwin in the Philos. Trans.
Vol. LXXVIII. Having charged an air-gun as forcibly as he well could the
air-cell and syringe became exceedingly hot, much more so than could be
ascribed to the friction in working it; it was then left about half an
hour to cool down to the temperature of the air, and a thermometer
having been previously fixed against a wall, the air was discharged in a
continual stream on its bulb, and it sunk many degrees. From these three
experiments of the steam in the exhausted receiver being deposited and
re-absorbed, when a part of the air is exhausted or re-admitted, and the
snow produced by the fountain of Hiero, and the extraordinary heat given
out in charging, and the cold produced in discharging an air-gun, there
is reason to conclude that when air is mechanically compressed the
elementary fluid heat is pressed out of it, and that when it is
mechanically expanded the same fluid heat is re-absorbed from the common
mass.
It is probable all other bodies as well as air attract heat from their
neighbours when they are mechanically expanded, and give it out when
they are mechanically condensed. Thus when a vibration of the particles
of hard bodies is excited by friction or by percussion, these particles
mutually recede from and approach each other reciprocally; at the times
of their recession from each other, the body becomes enlarged in bulk,
and is then in a condition to attract heat from those in its vicinity
with great and sudden power; at the times of their approach to each
other this heat is again given out, but the bodies in contact having in
the mean while received the heat they had thus lost, from other bodies
behind them, do not so suddenly or so forcibly re-absorb the heat again
from the body in vibration; hence it remains on its surface like the
electric fluid on a rubbed glass globe, and for the same reason, because
there is no good conductor to take it up again. Hence at every vibration
more and more heat is acquired and stands loose upon the surface; as in
filing metals or rubbing glass tubes; and thus a smith with a few
strokes on a nail on his anvil can make it hot enough to light a
brimstone-match; and hence in striking flint and steel together heat
enough is produced to vitrify the parts thus strucken off, the quantity
of which heat is again probably increased by the new chemical
combination.
II. The analogy between the phenomena of the electric fluid and of heat
furnishes another argument in support of the existence of heat as a
gravitating fluid. 1. They are both accumulated by friction on the
excited body. 2. They are propagated easily or with difficalty along the
same classes of bodies; with ease by metals, with less ease by water;
and with difficulty by resins, bees-wax, silk, air, and glass. Thus
glass canes or canes of sealing-wax may be melted by a blow-pipe or a
candle within a quarter of an inch of the fingers which hold them,
without any inconvenient heat, while a pin or other metallic substance
applyed to the flame of a candle so readily conducts the heat as
immediately to burn the fingers. Hence clothes of silk keep the body
warmer than clothes of linen of equal thickness, by confining the heat
upon the body. And hence plains are so much warmer than the summits of
mountains by the greater density of the air confining the acquired heat
upon them. 3. They both give out light in their passage through air,
perhaps not in their passage through a vacuum. 4. They both of them fuse
or vitrify metals. 5. Bodies after being electrized if they are
mechanically extended will receive a greater quantity of electricity, as
in Dr. Franklin's experiment of the chain in the tankard; the same seems
true in respect to heat as explained above. 6. Both heat and electricity
contribute to suspend steam in the atmosphere by producing or increasing
the repulsion of its particles. 7. They both gravitate, when they have
been accumulated, till they find their equilibrium.
If we add to the above the many chemical experiments which receive an
easy and elegant explanation from the supposed matter of heat, as
employed in the works of Bergman and Lavoisier, I think we may
reasonably allow of its existence as an element, occasionally combined
with other bodies, and occasionally existing as a fluid, like the
electric fluid gravitating amongst them, and that hence it may be
propagated from the central fires of the earth to the whole mass, and
contribute to preserve the mean heat of the earth, which in this country
is about 48 degrees but variable from the greater or less effect of the
sun's heat in different climates, so well explained in Mr. Kirwan's
Treatise on the Temperature of different Latitudes. 1787, Elmsly.
London.
NOTE VIII.--MEMNON'S LYRE.
_So to the sacred Sun in Memnon's fane
Spontaneous concords quired the matin strain._
CANTO I. l. 183.
The gigantic statue of Memnon in his temple at Thebes had a lyre in his
hands, which many credible writers assure us, sounded when the rising
sun shone upon it. Some philosophers have supposed that the sun's light
possesses a mechanical impulse, and that the sounds abovementioned might
be thence produced. Mr. Michell constructed a very tender horizontal
balance, as related by Dr. Priestley in his history of light and
colours, for this purpose, but some experiments with this balance which
I saw made by the late Dr. Powel, who threw the focus of a large
reflector on one extremity of it, were not conclusive either way, as the
copper leaf of the balance approached in one experiment and receded in
another.
There are however methods by which either a rotative or alternating
motion may be produced by very moderate degrees of heat. If a straight
glass tube, such as are used for barometers, be suspended horizontally
before a fire, like a roasting spit, it will revolve by intervals; for
as glass is a bad conductor of heat the side next the fire becomes
heated sooner than the opposite side, and the tube becomes bent into a
bow with the external part of the curve towards the fire, this curve
then falls down and produces a fourth part of a revolution of the glass
tube, which thus revolves with intermediate pauses.
Another alternating motion I have seen produced by suspending a glass
tube about eight inches long with bulbs at each end on a centre like a
scale beam. This curious machine is filled about one third part with
purest spirit of wine, the other two thirds being a vacuum, and is
called a pulse-glass, if it be placed in a box before the fire, so that
either bulb, as it rises, may become shaded from the fire, and exposed
to it when it descends, an alternate libration of it is produced. For
spirit of wine in vacuo emits steam by a very small degree of heat, and
this steam forces the spirit beneath it up into the upper bulb, which
therefore descends. It is probable such a machine on a larger scale
might be of use to open the doors or windows of hot-houses or mellon-
frames, when the air within them should become too much heated, or might
be employed in more important mechanical purposes.
On travelling through a hot summer's day in a chaise with a box covered
with leather on the fore-axle-tree, I observed, as the sun shone upon
the black leather, the box began to open its lid, which at noon rose
above a foot, and could not without great force be pressed down; and
which gradually closed again as the sun declined in the evening. This I
suppose might with still greater facility be applied to the purpose of
opening melon-frames or the sashes of hot-houses.
The statue of Memnon was overthrown and sawed in two by Cambyses to
discover its internal structure, and is said still to exist. See
Savary's Letters on Egypt. The truncated statue is said for many
centuries to have saluted the rising sun with chearful tones, and the
setting sun with melancholy ones.
NOTE IX.--LUMINOUS INSECTS.
_Star of the earth, and diamond of the night._
CANTO I. l. 196.
There are eighteen species of Lampyris or glow-worm, according to
Linneus, some of which are found in almost every part of the world. In
many of the species the females have no wings, and are supposed to be
discovered by the winged males by their shining in the night. They
become much more lucid when they put themselves in motion, which would
seem to indicate that their light is owing to their respiration; in
which process it is probable phosphoric acid is produced by the
combination of vital air with some part of the blood, and that light is
given out through their transparent bodies by this slow internal
combustion.
There is a fire-fly of the beetle-kind described in the Dict. Raisonné
under the name of Acudia, which is said to be two inches long, and
inhabits the West-Indies and South America; the natives use them instead
of candles, putting from one to three of them under a glass. Madam
Merian says, that at Surinam the light of this fly is so great, that she
saw sufficiently well by one of them to paint and finish one of the
figures of them in her work on insects. The largest and oldest of them
are said to become four inches long, and to shine like a shooting star
as they fly, and are thence called Lantern-bearers. The use of this
light to the insect itself seems to be that it may not fly against
objects in the night; by which contrivance these insects are enabled to
procure their sustenance either by night or day, as their wants may
require, or their numerous enemies permit them; whereas some of our
beetles have eyes adapted only to the night, and if they happen to come
abroad too soon in the evening are so dazzled that they fly against
every thing in their way. See note on Phosphorus, No. X.
In some seas, as particularly about the coast of Malabar, as a ship
floats along, it seems during the night to be surrounded with fire, and
to leave a long tract of light behind it. Whenever the sea is gently
agitated it seems converted into little stars, every drop as it breaks
emits light, like bodies electrified in the dark. Mr. Bomare says, that
when he was at the port of Cettes in Languedoc, and bathing with a
companion in the sea after a very hot day, they both appeared covered
with fire after every immersion, and that laying his wet hand on the arm
of his companion, who had not then dipped himself, the exact mark of his
hand and fingers was seen in characters of fire. As numerous microscopic
insects are found in this shining water, its light has been generally
ascribed to them, though it seems probable that fish-slime in hot
countries may become in such a state of incipient putrefaction as to
give light, especially when by agitation it is more exposed to the air;
otherwise it is not easy to explain why agitation should be necessary to
produce this marine light. See note on Phosphorus No. X.
NOTE X.--PHOSPHORUS.
_Or mark in shining letters Kunckel's name
In the pale phosphor's self-consuming flame._
CANTO I. l. 231.
Kunckel, a native of Hamburgh, was the first who discovered to the world
the process for producing phosphorus; though Brandt and Boyle were
likewise said to have previously had the art of making it. It was
obtained from sal microcosmicum by evaporation in the form of an acid,
but has since been found in other animal substances, as in the ashes of
bones, and even in some vegetables, as in wheat flour. Keir's chemical
Dict. This phosphoric acid is like all other acids united with vital
air, and requires to be treated with charcoal or phlogiston to deprive
it of this air, it then becomes a kind of animal sulphur, but of so
inflammable a nature, that on the access of air it takes fire
spontaneously, and as it burns becomes again united with vital air, and
re-assumes its form of phosphoric acid.
As animal respiration seems to be a kind of slow combustion, in which it
is probable that phosphoric acid is produced by the union of phosphorus
with the vital air, so it is also probable that phosphoric acid is
produced in the excretory or respiratory vessels of luminous insects, as
the glow-worm and fire-fly, and some marine insects. From the same
principle I suppose the light from putrid fish, as from the heads of
hadocks, and from putrid veal, and from rotten wood in a certain state
of their putrefaction, is produced, and phosphorus thus slowly combined
with air is changed into phosphoric acid. The light from the Bolognian
stone, and from calcined shells, and from white paper, and linen after
having been exposed for a time to the sun's light, seem to produce
either the phosphoric or some other kind of acid from the sulphurous or
phlogistic matter which they contain. See note on Beccari's shells. l.
180.
There is another process seems similar to this slow combustion, and that
is _bleaching_. By the warmth and light of the sun the water sprinkled
upon linen or cotton cloth seems to be decomposed, (if we credit the
theory of M. Lavoisier,) and a part of the vital air thus set at liberty
and uncombined and not being in its elastic form, more easily dissolves
the colouring or phlogistic matter of the cloth, and produces a new
acid, which is itself colourless, or is washed out of the cloth by
water. The new process of bleaching confirms a part of this theory, for
by uniting much vital air to marine acid by distilling it from
manganese, on dipping the cloth to be bleached in water repleat with
this super-aerated marine acid, the colouring matter disappears
immediately, sooner indeed in cotton than in linen. See note XXXIV.
There is another process which I suspect bears analogy to these above-
mentioned, and that is the rancidity of animal fat, as of bacon; if
bacon be hung up in a warm kitchen, with much salt adhering on the
outside of it, the fat part of it soon becomes yellow and rancid; if it
be washed with much cold water after it has imbibed the salt, and just
before it is hung up, I am well informed, that it will not become
rancid, or in very slight degrees. In the former case I imagine the salt
on the surface of the bacon attracts water during the cold of the night,
which is evaporated during the day, and that in this evaporation a part
of the water becomes decomposed, as in bleaching, and its vital air
uniting with greater facility in its unelastic state with the animal
fat, produces an acid, perhaps of the phosphoric kind, which being of a
fixed nature lies upon the bacon, giving it the yellow colour and rancid
taste. It is remarkable that the super-aerated marine acid does not
bleach living animal substances, at least it did not whiten a part of my
hand which I for some minutes exposed to it.
NOTE XI.--STEAM-ENGINE.
_Quick moves the balanced beam, of giant-birth,
Wields his large limbs, and nodding shakes the earth._
CANTO I. l. 261.
The expansive force of steam was known in some degree to the antients,
Hero of Alexandria describes an application of it to produce a rotative
motion by the re-action of steam issuing from a sphere mounted upon an
axis, through two small tubes bent into tangents, and issuing from the
opposite sides of the equatorial diameter of the sphere, the sphere was
supplied with steam by a pipe communicating with a pan of boiling water,
and entering the sphere at one of its poles.
A french writer about the year 1630 describes a method of raising water
to the upper part of a house by filling a chamber with steam, and
suffering it to condense of itself, but it seems to have been mere
theory, as his method was scarcely practicable as he describes it. In
1655 the Marquis of Worcester mentions a method of raising water by fire
in his Century of Inventions, but he seems only to have availed himself
of the expansive force and not to have known the advantages arising from
condensing the steam by an injection of cold water. This latter and most
important improvement seems to have been made by Capt. Savery sometime
prior to 1698, for in that year his patent for the use of that invention
was confirmed by act of parliament. This gentleman appears to have been
the first who reduced the machine to practice and exhibited it in an
useful form. This method consisted only in expelling the air from a
vessel by steam and condensing the steam by an injection of cold water,
which making a vacuum, the pressure of the atmosphere forced the water
to ascend into the steam-vessel through a pipe of 24 to 26 feet high,
and by the admission of dense steam from the boiler, forcing the water
in the steam-vessel to ascend to the height desired. This construction
was defective because it required very strong vessels to resist the
force of the steam, and because an enormous quantity of steam was
condensed by coming in contact with the cold water in the steam-vessel.
About or soon after that time M. Papin attempted a steam-engine on
similar principles but rather more defective in its construction.
The next improvement was made very soon afterwards by Messrs. Newcomen
and Cawley of Dartmouth, it consisted in employing for the steam-vessel
a hollow cylinder, shut at bottom and open at top, furnished with a
piston sliding easily up and down in it, and made tight by oakum or
hemp, and covered with water. This piston is suspended by chains from
one end of a beam, moveable upon an axis in the middle of its length, to
the other end of this beam are suspended the pump-rods.
The danger of bursting the vessels was avoided in this machine, as
however high the water was to be raised it was not necessary to increase
the density of the steam but only to enlarge the diameter of the
cylinder.
Another advantage was, that the cylinder not being made so cold as in
Savary's method, much less steam was lost in filling it after each
condensation.
The machine however still remained imperfect, for the cold water thrown
into the cylinder acquired heat from the steam it condensed, and being
in a vessel exhausted of air it produced steam itself, which in part
resisted the action of the atmosphere on the piston; were this remedied
by throwing in more cold water the destruction of steam in the next
filling of the cylinder would be proportionally increased. It has
therefore in practice been found adviseable not to load these engines
with columns of water weighing more than seven pounds for each square
inch of the area of the piston. The bulk of water when converted into
steam remained unknown until Mr. J. Watt, then of Glasgow, in 1764,
determined it to be about 1800 times more rare than water. It soon
occurred to Mr. Watt that a perfect engine would be that in which no
steam should be condensed in filling the cylinder, and in which the
steam should be so perfectly cooled as to produce nearly a perfect
vacuum.
Mr. Watt having ascertained the degree of heat in which water boiled in
vacuo, and under progressive degrees of pressure, and instructed by Dr.
Black's discovery of latent heat, having calculated the quantity of cold
water necessary to condense certain quantities of steam so far as to
produce the exhaustion required, he made a communication from the
cylinder to a cold vessel previously exhausted of air and water, into
which the steam rushed by its elasticity, and became immediately
condensed. He then adapted a cover to the cylinder and admitted steam
above the piston to press it down instead of air, and instead of
applying water he used oil or grease to fill the pores of the oakum and
to lubricate the cylinder.
He next applied a pump to extract the injection water, the condensed
steam, and the air, from the condensing vessel, every stroke of the
engine.
To prevent the cooling of the cylinder by the contact of the external
air, he surrounded it with a case containing steam, which he again
protected by a covering of matters which conduct heat slowly.
This construction presented an easy means of regulating the power of the
engine, for the steam being the acting power, as the pipe which admits
it from the boiler is more or less opened, a greater or smaller quantity
can enter during the time of a stroke, and consequently the engine can
act with exactly the necessary degree of energy.
Mr. Watt gained a patent for his engine in 1768, but the further
persecution of his designs were delayed by other avocations till 1775,
when in conjunction with Mr. Boulton of Soho near Birmingham, numerous
experiments were made on a large scale by their united ingenuity, and
great improvements added to the machinery, and an act of parliament
obtained for the prolongation of their patent for twenty-five years,
they have since that time drained many of the deep mines in Cornwall,
which but for the happy union of such genius must immediately have
ceased to work. One of these engines works a pump of eighteen inches
diameter, and upwards of 100 fathom or 600 feet high, at the rate of ten
to twelve strokes of seven feet long each, in a minute, and that with
one fifth part of the coals which a common engine would have taken to do
the same work. The power of this engine may be easier comprehended by
saying that it raised a weight equal to 81000 pounds 80 feet high in a
minute, which is equal to the combined action of 200 good horses. In
Newcomen's engine this would have required a cylinder of the enormous
diameter of 120 inches or ten feet, but as in this engine of Mr. Watt
and Mr. Boulton the steam acts, and a vacuum is made, alternately above
and below the piston, the power exerted is double to what the same
cylinder would otherways produce, and is further augmented by an
inequality in the length of the two ends of the lever.
These gentlemen have also by other contrivances applied their engines to
the turning of mills for almost every purpose, of which that great pile
of machinery the Albion Mill is a well known instance. Forges, slitting
mills, and other great works are erected where nature has furnished no
running water, and future times may boast that this grand and useful
engine was invented and perfected in our own country.
Since the above article went to the press the Albion Mill is no more; it
is supposed to have been set on fire by interested or malicious
incendaries, and is burnt to the ground. Whence London has lost the
credit and the advantage of possessing the most powerful machine in the
world!
NOTE XII.--FROST.
_In phalanx firm the fiend of Frost assail._
CANTO I. l. 439.
The cause of the expansion of water during its conversion into ice is
not yet well ascertained, it was supposed to have been owing to the air
being set at liberty in the act of congelation which was before
dissolved in the water, and the many air bubbles in ice were thought to
countenance this opinion. But the great force with which ice expands
during its congelation, so as to burst iron bombs and coehorns,
according to the experiments of Major Williams at Quebec, invalidates
this idea of the cause of it, and may sometime be brought into use as a
means of breaking rocks in mining, or projecting cannon-balls, or for
other mechanical purposes, if the means of producing congelation should
ever be discovered to be as easy as the means of producing combustion.
Mr. de Mairan attributes the increase of bulk of frozen water to the
different arrangement of the particles of it in crystallization, as they
are constantly joined at an angle of 60 degrees; and must by this
disposition he thinks occupy a greater volume than if they were
parallel. He found the augmentation of the water during freezing to
amount to one-fourteenth, one-eighteenth, one-nineteenth, and when the
water was previously purged of air to only one-twenty-second part. He
adds that a piece of ice, which was at first only one-fourteenth part
specifically lighter than water, on being exposed some days to the frost
became one-twelfth lighter than water. Hence he thinks ice by being
exposed to greater cold still increases in volume, and to this
attributes the bursting of ice in ponds and on the glaciers. See Lewis's
Commerce of Arts, p. 257. and the note on Muschus in the other volume of
this work.
This expansion of ice well accounts for the greater mischief done by
vernal frosts attended with moisture, (as by hoar-frosts,) than by the
dry frosts called black frosts. Mr. Lawrence in a letter to Mr. Bradley
complains that the dale-mist attended with a frost on may-day had
destroyed all his tender fruits; though there was a sharper frost the
night before without a mist, that did him no injury; and adds, that a
garden not a stone's throw from his own on a higher situation, being
above the dale-mist, had received no damage. Bradley, Vol. II. p. 232.
Mr. Hunter by very curious experiments discovered that the living
principle in fish, in vegetables, and even in eggs and seeds, possesses
a power of resisting congelation. Phil. Trans. There can be no doubt but
that the exertions of animals to avoid the pain of cold may produce in
them a greater quantity of heat, at least for a time, but that
vegetables, eggs, or seeds, should possess such a quality is truly
wonderful. Others have imagined that animals possess a power of
preventing themselves from becoming much warmer than 98 degrees of heat,
when immersed in an atmosphere above that degree of heat. It is true
that the increased exhalation from their bodies will in some measure
cool them, as much heat is carried off by the evaporation of fluids, but
this is a chemical not an animal process. The experiments made by those
who continued many minutes in the air of a room heated so much above any
natural atmospheric heat, do not seem conclusive, as they remained in it
a less time than would have been necessary to have heated a mass of beef
of the same magnitude, and the circulation of the blood in living
animals, by perpetually bringing new supplies of fluid to the skin,
would prevent the external surface from becoming hot much sooner than
the whole mass. And thirdly, there appears no power of animal bodies to
produce cold in diseases, as in scarlet fever, in which the increased
action of the vessels of the skin produces heat and contributes to
exhaust the animal power already too much weakened.
It has been thought by many that frosts meliorate the ground, and that
they are in general salubrious to mankind. In respect to the former it
is now well known that ice or snow contain no nitrous particles, and
though frost by enlarging the bulk of moist clay leaves it softer for a
time after the thaw, yet as soon as the water exhales, the clay becomes
as hard as before, being pressed together by the incumbent atmosphere,
and by its self-attraction, called _setting_ by the potters. Add to this
that on the coasts of Africa, where frost is unknown, the fertility of
the soil is almost beyond our conceptions of it. In respect to the
general salubrity of frosty seasons the bills of mortality are an
evidence in the negative, as in long frosts many weakly and old people
perish from debility occasioned by the cold, and many classes of birds
and other wild animals are benumbed by the cold or destroyed by the
consequent scarcity of food, and many tender vegetables perish from the
degree of cold.
I do not think it should be objected to this doctrine that there are
moist days attended with a brisk cold wind when no visible ice appears,
and which are yet more disagreeable and destructive than frosty weather.
For on these days the cold moisture, which is deposited on the skin is
there evaporated and thus produces a degree of cold perhaps greater than
the milder frosts. Whence even in such days both the disagreeable
sensations and insalubrious effects belong to the cause abovementioned,
viz. the intensity of the cold. Add to this that in these cold moist
days as we pass along or as the wind blows upon us, a new sheet of cold
water is as it were perpetually applied to us and hangs upon our bodies,
now as water is 800 times denser than air and is a much better conductor
of heat, we are starved with cold like those who go into a cold bath,
both by the great number of particles in contact with the skin and their
greater facility of receiving our heat.
It may nevertheless be true that snows of long duration in our winters
may be less injurious to vegetation than great rains and shorter frosts,
for two reasons. 1. Because great rains carry down many thousand pounds
worth of the best part of the manure off the lands into the sea, whereas
snow dissolves more gradually and thence carries away less from the
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