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 32° 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

land; any one may distinguish a snow-flood from a rain-flood by the

transparency of the water. Hence hills or fields with considerable

inclination of surface should be ploughed horizontally that the furrows

may stay the water from showers till it deposits its mud. 2. Snow

protects vegetables from the severity of the frost, since it is always

in a state of thaw where it is in contact with the earth; as the earth's

heat is about 48° and the heat of thawing snow is 32° the vegetables

between them are kept in a degree of heat about 40, by which many of

them are preserved. See note on Muschus, Vol. II. of this work.

NOTE XIII.--ELECTRICITY

_Cold from each point cerulean lustres gleam._

CANTO I. l. 339.

ELECTRIC POINTS.

There was an idle dispute whether knobs or points were preferable on the

top of conductors for the defence of houses. The design of these

conductors is to permit the electric matter accumulated in the clouds to

pass through them into the earth in a smaller continued stream as the

cloud approaches, before it comes to what is termed striking distance;

now as it is well known that accumulated electricity will pass to points

at a much greater distance than it will to knobs there can be no doubt

of their preference; and it would seem that the finer the point and the

less liable to become rusty the better, as it would take off the

lightening while it was still at a greater distance, and by that means

preserve a greater extent of building; the very extremity of the point

should be of pure silver or gold, and might be branched into a kind of

brush, since one small point can not be supposed to receive so great a

quantity as a thicker bar might conduct into the earth.

If an insulated metallic ball is armed with a point, like a needle,

projecting from one part of it, the electric fluid will be seen in the

dark to pass off from this point, so long as the ball is kept supplied

with electricity. The reason of this is not difficult to comprehend,

every part of the electric atmosphere which surrounds the insulated ball

is attracted to that ball by a large surface of it, whereas the electric

atmosphere which is near the extremity of the needle is attracted to it

by only a single point, in consequence the particles of electric matter

near the surface of the ball approach towards it and push off by their

greater gravitation the particles of electric matter over the point of

the needle in a continued stream.

Something like this happens in respect to the diffusion of oil on water

from a pointed cork, an experiment which was many years ago shewn me by

Dr. Franklin; he cut a piece of cork about the size of a letter-wafer

and left on one edge of it a point about a sixth of an inch in length

projecting as a tangent to the circumference. This was dipped in oil and

thrown on a pond of water and continued to revolve as the oil left the

point for a great many minutes. The oil descends from the floating cork

upon the water being diffused upon it without friction and perhaps

without contact; but its going off at the point so forcibly as to make

the cork revolve in a contrary direction seems analogous to the

departure of the electric fluid from points.

Can any thing similar to either of these happen in respect to the

earth's atmosphere and give occasion to the breezes on the tops of

mountains, which may be considered as points on the earths

circumference?

FAIRY-RINGS.

There is a phenomenon supposed to be electric which is yet unaccounted

for, I mean the Fairy-rings, as they are called, so often seen on the

grass. The numerous flashes of lightning which occur every summer are, I

believe, generally discharged on the earth, and but seldom (if ever)

from one cloud to another. Moist trees are the most frequent conductors

of these flashes of lightning, and I am informed by purchasers of wood

that innumerable trees are thus cracked and injured. At other times

larger parts or prominences of clouds gradually sinking as they move

along, are discharged on the moisture parts of grassy plains. Now this

knob or corner of a cloud in being attracted by the earth will become

nearly cylindrical, as loose wool would do when drawn out into a thread,

and will strike the earth with a stream of electricity perhaps two or

ten yards in diameter. Now as a stream of electricity displaces the air

it passes through, it is plain no part of the grass can be burnt by it,

but just the external ring of this cylinder where the grass can have

access to the air, since without air nothing can be calcined. This earth

after having been so calcined becomes a richer soil, and either funguses

or a bluer grass for many years mark the place. That lightning displaces

the air in its passage is evinced by the loud crack that succeeds it,

which is owing to the sides of the aerial vacuum clapping together when

the lightning is withdrawn. That nothing will calcine without air is now

well understood from the acids produced in the burning of phlogistic

substances, and may be agreeably seen by suspending a paper on an iron

prong and putting it into the centre of the blaze of an iron-furnace; it

may be held there some seconds and may be again withdrawn without its

being burnt, if it be passed quickly into the flame and out again

through the external part of it which is in contact with the air. I know

some circles of many yards diameter of this kind near Foremark in

Derbyshire which annually produce large white funguses and stronger

grass, and have done so, I am informed, above thirty years. This

increased fertility of the ground by calcination or charring, and its

continuing to operate so many years is well worth the attention of the

farmer, and shews the use of paring and burning new turf in agriculture,

which produces its effect not so much by the ashes of the vegetable

fibres as by charring the soil which adheres to them.

These situations, whether from eminence or from moisture, which were

proper once to attract and discharge a thunder-cloud, are more liable

again to experience the same. Hence many fairy-rings are often seen near

each other either without intersecting each other, as I saw this summer

in a garden in Nottinghamshire, or intersecting each other as described

on Arthur's seat near Edinburgh in the Edinb. Trans. Vol. II. p. 3.

NOTE XIV.--BUDS AND BULBS.

_Where dwell my vegetative realms benumb'd

In buds imprison'd, or in bulbs intomb'd._

CANTO I. l. 459.

A tree is properly speaking a family or swarm of buds, each bud being an

individual plant, for if one of these buds be torn or cut out and

planted in the earth with a glass cup inverted over it to prevent its

exhalation from being at first greater than its power of absorption, it

will produce a tree similar to its parent; each bud has a leaf, which is

its lungs, appropriated to it, and the bark of the tree is a congeries

of the roots of these individual buds, whence old hollow trees are often

seen to have some branches flourish with vigour after the internal wood

is almost intirely decayed and vanished. According to this idea Linneus

has observed that trees and shrubs are roots above ground, for if a tree

be inverted leaves will grow from the root-part and roots from the

trunk-part. Phil. Bot p. 39. Hence it appears that vegetables have two

methods of propagating themselves, the oviparous as by seeds, and the

viviparous as by their buds and bulbs, and that the individual plants,

whether from seeds or buds or bulbs, are all annual productions like

many kinds of insects as the silk-worm, the parent perishing in the

autumn after having produced an embryon, which lies in a torpid state

during the winter, and is matured in the succeeding summer. Hence

Linneus names buds and bulbs the winter-cradles of the plant or

hybernacula, and might have given the same term to seeds. In warm

climates few plants produce buds, as the vegetable life can be

compleated in one summer, and hence the hybernacle is not wanted; in

cold climates also some plants do not produce buds, as philadelphus,

frangula, viburnum, ivy, heath, wood-nightshade, rue, geranium.

The bulbs of plants are another kind of winter-cradle, or hybernacle,

adhering to the descending trunk, and are found in the perennial

herbaceous plants which are too tender to bear the cold of the winter.

The production of these subterraneous winter lodges, is not yet perhaps

clearly understood, they have been distributed by Linneus according to

their forms into scaly, solid, coated, and jointed bulbs, which however

does not elucidate their manner of production. As the buds of trees may

be truly esteemed individual annual plants, their roots constituting the

bark of the tree, it follows that these roots (viz. of each individual

bud) spread themselves over the last years bark, making a new bark over

the old one, and thence descending cover with a new bark the old roots

also in the same manner. A similar circumstance I suppose to happen in

some herbaceous plants, that is, a new bark is annually produced over

the old root, and thus for some years at least the old root or caudex

increases in size and puts up new stems. As these roots increase in size

the central part I suppose changes like the internal wood of a tree and

does not possess any vegetable life, and therefore gives out no fibres

or rootlets, and hence appears bitten off, as in valerian, plantain, and

devil's-bit. And this decay of the central part of the root I suppose

has given occasion to the belief of the root-fibres drawing down the

bulb so much insisted on by Mr. Milne in his Botanical Dictionary, Art.

Bulb.

From the observations and drawings of various kinds of bulbous roots at

different times of their growth, sent me by a young lady of nice

observation, it appears probable that all bulbous roots properly so

called perish annually in this climate: Bradley, Miller, and the Author

of Spectacle de la Nature, observe that the tulip annually renews its

bulb, for the stalk of the old flower is found under the old dry coat

but on the outside of the new bulb. This large new bulb is the flowering

bulb, but besides this there are other small new bulbs produced between

the coats of this large one but from the same caudex, (or circle from

which the root-fibres spring;) these small bulbs are leaf-bearing bulbs,

and renew themselves annually with increasing size till they bear

flowers.

Miss ---- favoured me with the following curious experiment: She took a

small tulip-root out of the earth when the green leaves were

sufficiently high to show the flower, and placed it in a glass of water;

the leaves and flower soon withered and the bulb became wrinkled and

soft, but put out one small side bulb and three bulbs beneath descending

an inch into the water by long processes from the caudex, the old bulb

in some weeks intirely decayed; on dissecting this monster, the middle

descending bulb was found by its process to adhere to the caudex and to

the old flower-stem, and the side ones were separated from the flower-

stem by a few shrivelled coats but adhered to the caudex. Whence she

concludes that these last were off-sets or leaf-bulbs which should have

been seen between the coats of the new flower-bulb if it had been left

to grow in the earth, and that the middle one would have been the new

flower-bulb. In some years (perhaps in wet seasons) the florists are

said to lose many of their tulip-roots by a similar process, the new

leaf-bulbs being produced beneath the old ones by an elongation of the

caudex without any new flower-bulbs.

By repeated dissections she observes that the leaf-bulbs or off-sets of

tulip, crocus, gladiolus, fritillary, are renewed in the same manner as

the flowering-bulbs, contrary to the opinion of many writers; this new

leaf-bulb is formed on the inside of the coats from whence the leaves

grow, and is more or less advanced in size as the outer coats and leaves

are more or less shrivelled. In examining tulip, iris, hyacinth, hare-

bell, the new bulb was invariably found _between_ the flower-stem and

the base of the innermost leaf of those roots which had flowered, and

_inclosed_ by the base of the innermost leaf in those roots which had

not flowered, in both cases adhering to the caudex or fleshy circle from

which the root-fibres spring.

Hence it is probable that the bulbs of hyacinths are renewed annually,

but that this is performed from the caudex within the old bulb, the

outer coat of which does not so shrivel as in crocus and fritillary and

hence this change is not so apparent. But I believe as soon as the

flower is advanced the new bulbs may be seen on dissection, nor does the

annual increase of the size of the root of cyclamen and of aletris

capensis militate against this annual renewal of them, since the leaf-

bulbs or off-sets, as described above, are increased in size as they are

annually renewed. See note on orchis, and on anthoxanthum, in Vol. II.

of this work.

NOTE XV.--SOLAR VOLCANOS.

_From the deep craters of his realms of fire

The whirling sun this ponderous planet hurld_.

CANTO II. l. 14.

Dr. Alexander Wilson, Professor of Astronomy at Glasgow, published a

paper in the Philosophical Transactions for 1774, demonstrating that the

spots in the sun's disk are real cavities, excavations through the

luminous material, which covers the other parts of the sun's surface.

One of these cavities he found to be about 4000 miles deep and many

times as wide. Some objections were made to this doctrine by M. De la

Laude in the Memoirs of the French Academy for the year 1776, which

however have been ably answered by Professor Wilson in reply in the

Philos. Trans. for 1783. Keil observes, in his Astronomical Lectures, p.

44, "We frequently see spots in the sun which are larger and broader not

only than Europe or Africa, but which even equal, if they do not exceed,

the surface of the whole terraqueous globe." Now that these cavities are

made in the sun's body by a process of nature similar to our earthquakes

does not seem improbable on several accounts. 1. Because from this

discovery of Dr. Wilson it appears that the internal parts of the sun

are not in a state of inflammation or of ejecting light, like the

external part or luminous ocean which covers it; and hence that a

greater degree of heat or inflammation and consequent expansion or

explosion may occasionally be produced in its internal or dark nucleus.

2. Because the solar spots or cavities are frequently increased or

diminished in size. 3. New ones are often produced. 4. And old ones

vanish. 5. Because there are brighter or more luminous parts of the

sun's disk, called faculae by Scheiner and Hevelius, which would seem to

be volcanos in the sun, or, as Dr. Wilson calls them, "eructations of

matter more luminous than that which covers the sun's surface." 6. To

which may be added that all the planets added together with their

satellites do not amount to more than one six hundred and fiftieth part

of the mass of the sun according to Sir Isaac Newton.

Now if it could be supposed that the planets were originally thrown out

of the sun by larger sun-quakes than those frequent ones which occasion

these spots or excavations above-mentioned, what would happen? 1.

According to the observations and opinion of Mr. Herschel the sun itself

and all its planets are moving forwards round some other centre with an

unknown velocity, which may be of opake matter corresponding with the

very antient and general idea of a chaos. Whence if a ponderous planet,

as Saturn, could be supposed to be projected from the sun by an

explosion, the motion of the sun itself might be at the same time

disturbed in such a manner as to prevent the planet from falling again

into it. 2. As the sun revolves round its own axis its form must be that

of an oblate spheroid like the earth, and therefore a body projected

from its surface perpendicularly upwards from that surface would not

rise perpendicularly from the sun's centre, unless it happened to be

projected exactly from either of its poles or from its equator. Whence

it may not be necessary that a planet if thus projected from the sun by

explosion should again fall into the sun. 3. They would part from the

sun's surface with the velocity with which that surface was moving, and

with the velocity acquired by the explosion, and would therefore move

round the sun in the same direction in which the sun rotates on its

axis, and perform eliptic orbits. 4. All the planets would move the same

way round the sun, from this first motion acquired at leaving its

surface, but their orbits would be inclined to each other according to

the distance of the part, where they were thrown out, from the sun's

equator. Hence those which were ejected near the sun's equator would

have orbits but little inclined to each other, as the primary planets;

the plain of all whose orbits are inclined but seven degrees and a half

from each other. Others which were ejected near the sun's poles would

have much more eccentric orbits, as they would partake so much less of

the sun's rotatory motion at the time they parted from his surface, and

would therefore be carried further from the sun by the velocity they had

gained by the explosion which ejected them, and become comets. 5. They

would all obey the same laws of motion in their revolutions round the

sun; this has been determined by astronomers, who have demonstrated that

they move through equal areas in equal times. 6. As their annual periods

would depend on the height they rose by the explosion, these would

differ in them all. 7. As their diurnal revolutions would depend on one

side of the exploded matter adhering more than the other at the time it

was torn off by the explosion, these would also differ in the different

planets, and not bear any proportion to their annual periods. Now as all

these circumstances coincide with the known laws of the planetary

system, they serve to strengthen this conjecture.

This coincidence of such a variety of circumstances induced M. de Buffon

to suppose that the planets were all struck off from the sun's surface

by the impact of a large comet, such as approached so near the sun's

disk, and with such amazing velocity, in the year 1680, and is expected

to return in 2255. But Mr. Buffon did not recollect that these comets

themselves are only planets with more eccentric orbits, and that

therefore it must be asked, what had previously struck off these comets

from the sun's body? 2. That if all these planets were struck off from

the sun at the same time, they must have been so near as to have

attracted each other and have formed one mass: 3. That we shall want new

causes for separating the secondary planets from the primary ones, and

must therefore look out for some other agent, as it does not appear how

the impulse of a comet could have made one planet roll round another at

the time they both of them were driven off from the surface of the sun.

If it should be asked, why new planets are not frequently ejected from

the sun? it may be answered, that after many large earthquakes many

vents are left for the elastic vapours to escape, and hence, by the

present appearance of the surface of our earth, earthquakes prodigiously

larger than any recorded in history have existed; the same circumstances

may have affected the sun, on whose surface there are appearances of

volcanos, as described above. Add to this, that some of the comets, and

even the georgium sidus, may, for ought we know to the contrary, have

been emitted from the sun in more modern days, and have been diverted

from their course, and thus prevented from returning into the sun, by

their approach to some of the older planets, which is somewhat

countenanced by the opinion several philosophers have maintained, that

the quantity of matter of the sun has decreased. Dr. Halley observed,

that by comparing the proportion which the periodical time of the moon

bore to that of the sun in former times, with the proportion between

them at present, that the moon is found to be somewhat accelerated in

respect to the sun. Pemberton's View of Sir Isaac Newton, p. 247. And so

large is the body of this mighty luminary, that all the planets thus

thrown out of it would make scarcely any perceptible diminution of it,

as mentioned above. The cavity mentioned above, as measured by Dr.

Wilson of 4000 miles in depth, not penetrating an hundredth part of the

sun's semi-diameter; and yet, as its width was many times greater than

its depth, was large enough to contain a greater body than our

terrestrial world.

I do not mean to conceal, that from the laws of gravity unfolded by Sir

Isaac Newton, supposing the sun to be a sphere and to have no

progressive motion, and not liable itself to be disturbed by the

supposed projection of the planets from it, that such planets must

return into the sun. The late Rev. William Ludlam, of Leicester, whose

genius never met with reward equal to its merits, in a letter to me,

dated January, 1787, after having shewn, as mentioned above, that

planets so projected from the sun would return to it, adds, "That a body

as large as the moon so projected, would disturb the motion of the earth

in its orbit, is certain; but the calculation of such disturbing forces

is difficult. The body in some circumstances might become a satellite,

and both move round their common centre of gravity, and that centre be

carried in an annual orbit round the sun."

There are other circumstances which might have concurred at the time of

such supposed explosions, which would render this idea not impossible.

1. The planets might be thrown out of the sun at the time the sun itself

was rising from chaos, and be attracted by other suns in their vicinity

rising at the same time out of chaos, which would prevent them from

returning into the sun. 2. The new planet in its course or ascent from

the sun, might explode and eject a satellite, or perhaps more than one,

and thus by its course being affected might not return into the sun. 3.

If more planets were ejected at the same time from the sun, they might

attract and disturb each others course at the time they left the body of

the sun, or very soon afterwards, when they would be so much nearer each

other.

NOTE XVI.--CALCAREOUS EARTH.

_While Ocean wrap'd it in his azure robe_.

CANTO II. l. 34.

From having observed that many of the highest mountains of the world

consist of lime-stone replete with shells, and that these mountains bear

the marks of having been lifted up by subterraneous fires from the

interior parts of the globe; and as lime-stone replete with shells is

found at the bottom of many of our deepest mines some philosophers have

concluded that the nucleus of the earth was for many ages covered with

water which was peopled with its adapted animals; that the shells and

bones of these animals in a long series of time produced solid strata in

the ocean surrounding the original nucleus.

These strata consist of the accumulated exuviae of shell-fish, the

animals perished age after age but their shells remained, and in

progression of time produced the amazing quantities of lime-stone which

almost cover the earth. Other marine animals called coralloids raised

walls and even mountains by the congeries of their calcareous

habitations, these perpendicular corralline rocks make some parts of the

Southern Ocean highly dangerous, as appears in the journals of Capt.

Cook. From contemplating the immense strata of lime-stone, both in

respect to their extent and thickness, formed from these shells of

animals, philosophers have been led to conclude that much of the water

of the sea has been converted into calcareous earth by passing through

their organs of digestion. The formation of calcareous earth seems more

particularly to be an animal process as the formation of clay belongs to

the vegetable economy; thus the shells of crabs and other testaceous

fish are annually reproduced from the mucous membrane beneath them; the

shells of eggs are first a mucous membrane, and the calculi of the

kidneys and those found in all other parts of our system which sometimes

contain calcareous earth, seem to originate from inflamed membranes; the

bones themselves consist of calcareous earth united with the phosphoric

or animal acid, which may be separated by dissolving the ashes of

calcined bones in the nitrous acid; the various secretions of animals,

as their saliva and urine, abound likewise with calcareous earth, as

appears by the incrustations about the teeth and the sediments of urine.

It is probable that animal mucus is a previous process towards the

formation of calcareous earth; and that all the calcareous earth in the

world which is seen in lime-stones, marbles, spars, alabasters, marls,

(which make up the greatest part of the earth's crust, as far as it has

yet been penetrated,) have been formed originally by animal and

vegetable bodies from the mass of water, and that by these means the

solid part of the terraqueous globe has perpetually been in an

increasing state and the water perpetually in a decreasing one.

After the mountains of shells and other recrements of aquatic animals

were elevated above the water the upper heaps of them were gradually

dissolved by rains and dews and oozing through were either perfectly

crystallized in smaller cavities and formed calcareous spar, or were

imperfectly crystallized on the roofs of larger cavities and produced

stalactes; or mixing with other undissolved shells beneath them formed

marbles, which were more or less crystallized and more or less pure; or

lastly, after being dissolved, the water was exhaled from them in such a

manner that the external parts became solid, and forming an arch

prevented the internal parts from approaching each other so near as to

become solid, and thus chalk was produced. I have specimens of chalk

formed at the root of several stalactites, and in their central parts;

and of other stalactites which are hollow like quills from a similar

cause, viz. from the external part of the stalactite hardening first by

its evaporation, and thus either attracting the internal dissolved

particles to the crust, or preventing them from approaching each other

so as to form a solid body. Of these I saw many hanging from the arched

roof of a cellar under the high street in Edinburgh.

If this dissolved limestone met with vitriolic acid it was converted

into alabaster, parting at the same time with its fixable air. If it met

with the fluor acid it became fluor; if with the siliceous acid, flint;

and when mixed with clay and sand, or either of them, acquires the name

of marl. And under one or other of these forms composes a great part of

the solid globe of the earth.

Another mode in which limestone appears is in the form of round

granulated particles, but slightly cohering together; of this kind a bed

extends over Lincoln heath, perhaps twenty miles long by ten wide. The

form of this calcareous sand, its angles having been rubbed off, and the

flatness of its bed, evinces that that part of the country was so formed

under water, the particles of sand having thus been rounded, like all

other rounded pebbles. This round form of calcareous sand and of other

larger pebbles is produced under water, partly by their being more or

less soluble in water, and hence the angular parts become dissolved,

first, by their exposing a larger surface to the action of the

menstruum, and secondly, from their attrition against each other by the

streams or tides, for a great length of time, successively as they were

collected, and perhaps when some of them had not acquired their hardest

state.

This calcareous sand has generally been called ketton-stone and believed

to resemble the spawn of fish, it has acquired a form so much rounder

than siliceous sand from its being of so much softer a texture and also

much more soluble in water. There are other soft calcareous stones

called tupha which are deposited from water on mosses, as at Matlock,

from which moss it is probable the water may receive something which

induces it the readier to part with its earth.

In some lime-stones the living animals seem to have been buried as well

as their shells during some great convulsion of nature, these shells

contain a black coaly substance within them, in others some phlogiston

or volatile alcali from the bodies of the dead animals remains mixed

with the stone, which is then called liver-stone as it emits a

sulphurous smell on being struck, and there is a stratum about six

inches thick extends a considerable way over the iron ore at Wingerworth

near Chesterfield in Derbyshire which seems evidently to have been

formed from the shells of fresh-water muscles.

There is however another source of calcareous earth besides the aquatic

one above described and that is from the recrements of land animals and

vegetables as found in marls, which consist of various mixtures of

calcareous earth, sand, and clay, all of them perhaps principally from

vegetable origin.

Dr. Hutton is of opinion that the rocks of marble have been softened by

fire into a fluid mass, which he thinks under immense pressure might be

done without the escape of their carbonic acid or fixed air. Edinb.

Transact. Vol. I. If this ingenious idea be allowed it might account for

the purity of some white marbles, as during their fluid state there

might be time for their partial impurities, whether from the bodies of

the animals which produced the shells or from other extraneous matter,

either to sublime to the uppermost part of the stratum or to subside to

the lowermost part of it. As a confirmation of this theory of Dr.

Hutton's it may be added that some calcareous stones are found mixed

with lime, and have thence lost a part of their fixed air or carbonic

gas, as the bath-stone, and on that account hardens on being exposed to

the air, and mixed with sulphur produces calcareous liver of sulphur.

Falconer on Bath-water. Vol. I. p. 156. and p. 257. Mr. Monnet found

lime in powder in the mountains of Auvergne, and suspected it of

volcanic origin. Kirwan's Min. p. 22.

NOTE XVII.--MORASSES.

_Gnomes! you then taught transuding dews to pass

Through time-fallen woods, and root-inwove morass_.

CANTO II. l. 115.

Where woods have repeatedly grown and perished morasses are in process

of time produced, and by their long roots fill up the interstices till

the whole becomes for many yards deep a mass of vegetation. This fact is

curiously verified by an account given many years ago by the Earl of

Cromartie, of which the following is a short abstract.

In the year 1651 the EARL OF CROMARTIE being then nineteen years of age

saw a plain in the parish of Lockburn covered over with a firm standing

wood, which was so old that not only the trees had no green leaves upon

them but the bark was totally thrown off, which he was there informed by

the old countrymen was the universal manner in which fir-woods

terminated, and that in twenty or thirty years the trees would cast

themselves up by the roots. About fifteen years after he had occasion to

travel the same way and observed that there was not a tree nor the

appearance of a root of any of them; but in their place the whole plain

where the wood stood was covered with a flat green moss or morass, and

on asking the country people what was become of the wood he was informed

that no one had been at the trouble to carry it away, but that it had

all been overturned by the wind, that the trees lay thick over each

other, and that the moss or bog had overgrown the whole timber, which

they added was occasioned by the moisture which came down from the high

hills above it and stagnated upon the plain, and that nobody could yet

pass over it, which however his Lordship was so incautious as to attempt

and slipt up to the arm-pits. Before the year 1699 that whole piece of

ground was become a solid moss wherein the peasants then dug turf or

peat, which however was not yet of the best sort. Philos. Trans. No.

330. Abridg. Vol. V. p. 272.

Morasses in great length of time undergo variety of changes, first by

elutriation, and afterwards by fermentation, and the consequent heat. 1.

By water perpetually oozing through them the most soluble parts are

first washed away, as the essential salts, these together with the salts

from animal recrements are carried down the rivers into the sea, where

all of them seem to decompose each other except the marine salt. Hence

the ashes of peat contain little or no vegetable alcali and are not used

in the countries, where peat constitutes the fuel of the lower people,

for the purpose of washing linen. The second thing which is always seen

oozing from morasses is iron in solution, which produces chalybeate

springs, from whence depositions of ochre and variety of iron ores. The

third elutriation seems to consist of vegetable acid, which by means

unknown appears to be converted into all other acids. 1. Into marine and

nitrous acids as mentioned above. 2. Into vitriolic acid which is found

in some morasses so plentifully as to preserve the bodies of animals

from putrefaction which have been buried in them, and this acid carried

away by rain and dews and meeting with calcareous earth produces gypsum

or alabaster, with clay it produces alum, and deprived of its vital air

produces sulphur. 3. Fluor acid which being washed away and meeting with

calcareous earth produces fluor or cubic spar. 4. The siliceous acid

which seems to have been disseminated in great quantity either by

solution in water or by solution in air, and appears to have produced

the sand in the sea uniting with calcareous earth previously dissolved

in that element, from which were afterwards formed some of the grit-

stone rocks by means of a siliceous or calcareous cement. By its union

with the calcareous earth of the morass other strata of siliceous sand

have been produced; and by the mixture of this with clay and lime arose

the beds of marl.

In other circumstances, probably where less moisture has prevailed,

morasses seem to have undergone a fermentation, as other vegetable

matter, new hay for instance is liable to do from the great quantity of

sugar it contains. From the great heat thus produced in the lower parts

of immense beds of morass the phlogistic part, or oil, or asphaltum,

becomes distilled, and rising into higher strata becomes again condensed

forming coal-beds of greater or less purity according to their greater

or less quantity of inflammable matter; at the same time the clay beds

become purer or less so, as the phlogistic part is more or less

completely exhaled from them. Though coal and clay are frequently

produced in this manner, yet I have no doubt, but that they are likewise

often produced by elutriation; in situations on declivities the clay is

washed away down into the valleys, and the phlogistic part or coal left

behind; this circumstance is seen in many valleys near the beds of

rivers, which are covered recently by a whitish impure clay, called

water-clay. See note XIX. XX. and XXIII.

LORD CROMARTIE has furnished another curious observation on morasses in

the paper above referred to. In a moss near the town of Eglin in Murray,

though there is no river or water which communicates with the moss, yet

for three or four feet of depth in the moss there are little shell-fish

resembling oysters with living fish in them in great quantities, though

no such fish are found in the adjacent rivers, nor even in the water

pits in the moss, but only in the solid substance of the moss. This

curious fact not only accounts for the shells sometimes found on the

surface of coals, and in the clay above them; but also for a thin

stratum of shells which sometimes exists over iron-ore.

NOTE XVIII.--IRON.

_Cold waves, immerged, the glowing mass congeal,

And turn to adamant the hissing Steel._

CANTO II. l. 191.

As iron is formed near the surface of the earth, it becomes exposed to

streams of water and of air more than most other metallic bodies, and

thence becomes combined with oxygene, or vital air, and appears very

frequently in its calciform state, as in variety of ochres. Manganese,

and zinc, and sometimes lead, are also found near the surface of the

earth, and on that account become combined with vital air and are

exhibited in their calciform state.

The avidity with which iron unites with oxygene, or vital air, in which

process much heat is given out from the combining materials, is shewn by

a curious experiment of M. Ingenhouz. A fine iron wire twisted spirally

is fixed to a cork, on the point of the spire is fixed a match made of

agaric dipped in solution of nitre; the match is then ignited, and the

wire with the cork put immediately into a bottle full of vital air, the

match first burns vividly, and the iron soon takes fire and consumes

with brilliant sparks till it is reduced to small brittle globules,

gaining an addition of about one third of its weight by its union, with

vital air. Annales de Chymie. Traité de Chimie, per Lavoisier, c. iii.

STEEL.

It is probably owing to a total deprivation of vital air which it holds

with so great avidity, that iron on being kept many hours or days in

ignited charcoal becomes converted into steel, and thence acquires the

faculty of being welded when red hot long before it melts, and also the

power of becoming hard when immersed in cold water; both which I suppose

depend on the same cause, that is, on its being a worse conductor of

heat than other metals; and hence the surface both acquires heat much

sooner, and loses it much sooner, than the internal parts of it, in this

circumstance resembling glass.

When steel is made very hot, and suddenly immerged in very cold water,

and moved about in it, the surface of the steel becomes cooled first,

and thus producing a kind of case or arch over the internal part,

prevents that internal part from contracting quite so much as it

otherwise would do, whence it becomes brittler and harder, like the

glass-drops called Prince Rupert's drops, which are made by dropping

melted glass into cold water. This idea is countenanced by the

circumstance that hardened steel is specifically lighter than steel

which is more gradually cooled. (Nicholson's Chemistry, p. 313.) Why the

brittleness and hardness of steel or glass should keep pace or be

companions to each other may be difficult to conceive.

When a steel spring is forcibly bent till it break, it requires less

power to bend it through the first inch than the second, and less

through the second than the third; the same I suppose to happen if a

wire be distended till it break by hanging weights to it; this shews

that the particles may be forced from each other to a small distance by

less power, than is necessary to make them recede to a greater distance;

in this circumstance perhaps the attraction of cohesion differs from

that of gravitation, which exerts its power inversely as the squares of

the distance. Hence it appears that if the innermost particles of a

steel bar, by cooling the external surface first, are kept from

approaching each other so nearly as they otherwise would do, that they

become in the situation of the particles on the convex side of a bent

spring, and can not be forced further from each other except by a

greater power than would have been necessary to have made them recede

thus far. And secondly, that if they be forced a little further from

each other they separate; this may be exemplified by laying two magnetic

needles parallel to each other, the contrary poles together, then

drawing them longitudinally from each other, they will slide with small

force till they begin to separate, and will then require a stronger

force to really separate them. Hence it appears, that hardness and

brittleness depend on the same circumstance, that the particles are

removed to a greater distance from each other and thus resist any power

more forcibly which is applied to displace them further, this

constitutes hardness. And secondly, if they are displaced by such

applied force they immediately separate, and this constitutes

brittleness.

Steel may be thus rendered too brittle for many purposes, on which

account artists have means of softening it again, by exposing it to

certain degrees of heat, for the construction of different kinds of

tools, which is called tempering it. Some artists plunge large tools in

very cold water as soon as they are compleatly ignited, and moving it

about, take it out as soon as it ceases to be luminous beneath the

water; it is then rubbed quickly with a file or on sand to clean the

surface, the heat which the metal still retains soon begins to produce a

succession of colours; if a hard temper be required, the piece is dipped

again and stirred about in cold water as soon as the yellow tinge

appears, if it be cooled when the purple tinge appears it becomes fit

for gravers' tools used in working upon metals; if cooled while blue it

is proper for springs. Nicholson's Chemistry, p. 313. Keir's Chemical

Dictionary.

MODERN PRODUCTION OF IRON.

The recent production of iron is evinced from the chalybeate waters

which flow from morasses which lie upon gravel-beds, and which must

therefore have produced iron after those gravel-beds were raised out of

the sea. On the south side of the road between Cheadle and Okeymoor in

Staffordshire, yellow stains of iron are seen to penetrate the gravel

from a thin morass on its surface. There is a fissure eight or ten feet

wide, in a gravel-bed on the eastern side of the hollow road ascending

the hill about a mile from Trentham in Staffordshire, leading toward

Drayton in Shropshire, which fissure is filled up with nodules of iron-

ore. A bank of sods is now raised against this fissure to prevent the

loose iron nodules from falling into the turnpike road, and thus this

natural curiosity is at present concealed from travellers. A similar

fissure in a bed of marl, and filled up with iron nodules and with some

large pieces of flint, is seen on the eastern side of the hollow road

ascending the hill from the turnpike house about a mile from Derby in

the road towards Burton. And another such fissure filled with iron

nodes, appears about half a mile from Newton-Solney in Derbyshire, in

the road to Burton, near the summit of the hill. These collections of

iron and of flint must have been produced posterior to the elevation of

all those hills, and were thence evidently of vegetable or animal

origin. To which should be added, that iron is found in general in beds

either near the surface of the earth, or stratified with clay coals or

argillaceous grit, which are themselves productions of the modern world,

that is, from the recrements of vegetables and air-breathing animals.

Not only iron but manganese, calamy, and even copper and lead appear in

some instances to have been of recent production. Iron and manganese are

detected in all vegetable productions, and it is probable other metallic

bodies might be found to exist in vegetable or animal matters, if we had

tests to detect them in very minute quantities. Manganese and calamy are

found in beds like iron near the surface of the earth, and in a

calciform state, which countenances their modern production. The recent

production of calamy, one of the ores of zinc, appears from its

frequently incrusting calcareous spar in its descent from the surface of

the earth into the uppermost fissures of the limestone mountains of

Derbyshire. That the calamy has been carried by its solution or

diffusion in water into these cavities, and not by its ascent from below

in form of steam, is evinced from its not only forming a crust over the

dogtooth spar, but by its afterwards dissolving or destroying the sparry

crystal. I have specimens of calamy in the form of dogtooth spar, two

inches high, which are hollow, and stand half an inch above the

diminished sparry crystal on which they were formed, like a sheath a

great deal too big for it; this seems to shew, that this process was

carried on in water, otherwise after the calamy had incrusted its spar,

and dissolved its surface, so as to form a hollow cavern over it, it

could not act further upon it except by the interposition of some

medium. As these spars and calamy are formed in the fissures of

mountains they must both have been formed after the elevation of those

mountains.

In respect to the recent production of copper, it was before observed in

note on Canto II. l. 394, that the summit of the grit-stone mountain at

Hawkstone in Shropshire, is tinged with copper, which from the

appearance of the blue stains seems to have descended to the parts of

the rock beneath. I have a calciform ore of copper consisting of the

hollow crusts of cubic cells, which has evidently been formed on

crystals of fluor, which it has eroded in the same manner as the calamy

erodes the calcareous crystals, from whence may be deduced in the same

manner, the aqueous solution or diffusion, as well as the recent

production of this calciform ore of copper.

Lead in small quantities is sometimes found in the fissures of coal-

beds, which fissures are previously covered with spar; and sometimes in

nodules of iron-ore. Of the former I have a specimen from near Caulk in

Derbyshire, and of the latter from Colebrook Dale in Shropshire. Though

all these facts shew that some metallic bodies are formed from vegetable

or animal recrements, as iron, and perhaps manganese and calamy, all

which are found near the surface of the earth; yet as the other metals

are found only in fissures of rocks, which penetrate to unknown depths,

they may be wholly or in part produced by ascending steams from

subterraneous fires, as mentioned in note on Canto II. l. 398.

SEPTARIA OF IRON-STONE.

Over some lime works at Walsall in Staffordshire, I observed some years

ago a stratum of iron earth about six inches thick, full of very large

cavities; these cavities were evidently produced when the material

passed from a semifluid state into a solid one; as the frit of the

potters, or a mixture of clay and water is liable to crack in drying;

which is owing to the further contraction of the internal part, after

the crust is become hard. These hollows are liable to receive extraneous

matter, as I believe gypsum, and sometimes spar, and even lead; a

curious specimen of the last was presented to me by Mr. Darby of

Colebrook Dale, which contains in its cavity some ounces of lead-ore.

But there are other septaria of iron-stone which seem to have had a very

different origin, their cavities having been formed in cooling or

congealing from an ignited state, as is ingeniously deduced by Dr.

Hutton from their internal structure. Edinb. Transact. Vol. I. p. 246.

The volcanic origin of these curious septaria appears to me to be

further evinced from their form and the places where they are found.

They consist of oblate spheroids and are found in many parts of the

earth totally detached from the beds in which they lie, as at East

Lothian in Scotland. Two of these, which now lie before me, were found

with many others immersed in argillaceous shale or shiver, surrounded by

broken limestone mountains at Bradbourn near Ashbourn in Derbyshire, and

were presented to me by Mr. Buxton, a gentleman of that town. One of

these is about fifteen inches in its equatorial diameter, and about six

inches in its polar one, and contains beautiful star-like septaria

incrusted and in part filled with calcareous spar. The other is about

eight inches in its equatorial diameter, and about four inches in its

polar diameter, and is quite solid, but shews on its internal surface

marks of different colours, as if a beginning separation had taken

place. Now as these septaria contain fifty per cent, of iron, according

to Dr. Hutton, they would soften or melt into a semifluid globule by

subterraneous fire by less heat than the limestone in their vicinity;

and if they were ejected through a hole or fissure would gain a circular

motion along with their progressive one by their greater friction or

adhesion to one side of the hole. This whirling motion would produce the

oblate spheroidical form which they possess, and which as far as I know

can not in any other way be accounted for. They would then harden in the

air as they rose into the colder parts of the atmosphere; and as they

descended into so soft a material as shale or shiver, their forms would

not be injured in their fall; and their presence in materials so

different from themselves becomes accounted for.

About the tropics of the large septarium above mentioned, are circular

eminent lines, such as might have been left if it had been coarsely

turned in a lathe. These lines seem to consist of a fluid matter, which

seems to have exsuded in circular zones, as their edges appear blunted

or retracted; and the septarium seems to have split easier in such

sections parallel to its equator. Now as the crust would first begin to

cool and harden after its ejection in a semifluid state, and the

equatorial diameter would become gradually enlarged as it rose in the

air; the internal parts being softer would slide beneath the polar

crust, which might crack and permit part of the semifluid to exsude, and

it is probable the adhesion would thus become less in sections parallel

to the equator. Which further confirms this idea of the production of

these curious septaria. A new-cast cannon ball red-hot with its crust

only solid, if it were shot into the air would probably burst in its

passage; as it would consist of a more fluid material than these

septaria; and thus by discharging a shower of liquid iron would produce

more dreadful combustion, if used in war, than could be effected by a

ball, which had been cooled and was heated again: since in the latter

case the ball could not have its internal parts made hotter than the

crust of it, without first loosing its form.

NOTE XIX.--FLINT.

_Transmute to glittering flints her chalky lands,

Or sink on Ocean's bed in countless sands._

CANTO II. l. 217.

1. SILICEOUS ROCKS.

The great masses of siliceous sand which lie in rocks upon the beds of

limestone, or which are stratified with clay, coal, and iron-ore, are

evidently produced in the decomposition of vegetable or animal matters,

as explained in the note on morasses. Hence the impressions of vegetable

roots and even whole trees are often found in sand-stone, as well as in

coals and iron-ore. In these sand-rocks both the siliceous acid and the

calcareous base seem to be produced from the materials of the morass;

for though the presence of a siliceous acid and of a calcareous base

have not yet been separately exhibited from flints, yet from the analogy

of flint to fluor, and gypsum, and marble, and from the conversion of

the latter into flint, there can be little doubt of their existence.

These siliceous sand-rocks are either held together by a siliceous

cement, or have a greater or less portion of clay in them, which in some

acts as a cement to the siliceous crystals, but in others is in such

great abundance that in burning them they become an imperfect porcelain

and are then used to repair the roads, as at Chesterfield in Derbyshire;

these are called argillaceous grit by Mr. Kirwan. In other places a

calcareous matter cements the crystals together; and in other places the

siliceous crystals lie in loose strata under the marl in the form of

white sand; as at Normington about a mile from Derby.

The lowest beds of siliceous sand-stone produced from morasses seem to

obtain their acid from the morass, and their calcareous base from the

limestone on which it rests; These beds possess a siliceous cement, and

from their greater purity and hardness are used for course grinding-

stones and scyth stones, and are situated on the edges of limestone

countries, having lost the other strata of coals, or clay, or iron,

which were originally produced above them. Such are the sand-rocks

incumbent on limestone near Matlock in Derbyshire. As these siliceous

sand-rocks contain no marine productions scattered amongst them, they

appear to have been elevated, torn to pieces, and many fragments of them

scattered over the adjacent country by explosions, from fires within the

morass from which they have been formed; and which dissipated every

thing inflammable above and beneath them, except some stains of iron,

with which they are in some places spotted. If these sand-rocks had been

accumulated beneath the sea, and elevated along with the beds of

limestone on which they rest, some vestiges of marine shells either in

their siliceous or calcareous state must have been discerned amongst

them.

2. SILICEOUS TREES.

In many of these sand-rocks are found the impressions of vegetable

roots, which seem to have been the most unchangeable parts of the plant,

as shells and shark's teeth are found in chalk-beds from their being the

most unchangeable parts of the animal. In other instances the wood

itself is penetrated, and whole trees converted into flint; specimens of

which I have by me, from near Coventry, and from a gravel-pit in

Shropshire near Child's Archal in the road to Drayton. Other polished

specimens of vegetable flints abound in the cabinets of the curious,

which evidently shew the concentric circles of woody fibres, and their

interstices filled with whiter siliceous matter, with the branching off

of the knots when cut horizontally, and the parallel lines of wood when

cut longitudinally, with uncommon beauty and variety. Of these I possess

some beautiful specimens, which were presented to me by the Earl of

Uxbridge.

The colours of these siliceous vegetables are generally brown, from the

iron, I suppose, or manganese, which induced them to crystallize or to

fuse more easily. Some of the cracks of the wood in drying are filled

with white flint or calcedony, and others of them remain hollow, lined

with innumerable small crystals tinged with iron, which I suppose had a

share in converting their calcareous matter into siliceous crystals,

because the crystals called Peak-diamonds are always found bedded in an

ochreous earth; and those called Bristol-stones are situated on

limestone coloured with iron. Mr. F. French presented me with a

congeries of siliceous crystals, which he gathered on the crater (as he

supposes) of an extinguished volcano at Cromach Water in Cumberland. The

crystals are about an inch high in the shape of dogtooth or calcareous

spar, covered with a dark ferruginous matter. The bed on which they rest

is about an inch in thickness, and is stained with iron on its

undersurface. This curious fossil shews the transmutation of calcareous

earth into siliceous, as much as the siliceous shells which abound in

the cabinets of the curious. There may sometime be discovered in this

age of science, a method of thus impregnating wood with liquid flint,

which would produce pillars for the support, and tiles for the covering

of houses, which would be uninflammable and endure as long as the earth

beneath them.

That some siliceous productions have been in a fluid state without much

heat at the time of their formation appears from the vegetable flints

above described not having quite lost their organized appearance; from

shells, and coralloids, and entrochi being converted into flint without

loosing their form; from the bason of calcedony round Giesar in Iceland;

and from the experiment of Mr. Bergman, who obtained thirteen regular

formed crystals by suffering the powder of quartz to remain in a vessel

with fluor acid for two years; these crystals were about the size of

small peas, and were not so hard as quartz. Opusc. de Terrâ Siliceâ, p.

33. Mr. Achard procured both calcareous and siliceous crystals, one from

calcareous earth, and the other from the earth of alum, both dissolved

in water impregnated with fixed air; the water filtrating very slowly

through a porous bottom of baked clay. See Journal de Physique, for

January, 1778.

3. AGATES, ONYXES, SCOTS-PEBBLES.

In small cavities of these sand-rocks, I am informed, the beautiful

siliceous nodules are found which are called Scot's-pebbles; and which

on being cut in different directions take the names of agates, onyxes,

sardonyxes, &c. according to the colours of the lines or strata which

they exhibit. Some of the nodules are hollow and filled with crystals,

others have a nucleus of less compact siliceous matter which is

generally white, surrounded with many concentric strata coloured with

iron, and other alternate strata of white agate or calcedony, sometimes

to the number of thirty.

I think these nodules bear evident marks of their having been in perfect

fusion by either heat alone, or by water and heat, under great pressure,

according to the ingenious theory of Dr. Hutton; but I do not imagine,

that they were injected into cavities from materials from without, but

that some vegetables or parts of vegetables containing more iron or

manganese than others, facilitated the compleat fusion, thus destroying

the vestiges of vegetable organization, which were conspicuous in the

siliceous trees above mentioned. Some of these nodules being hollow and

lined with crystals, and others containing a nucleus of white siliceous

matter of a looser texture, shew they were composed of the materials

then existing in the cavity; which consisting before of loose sand, must

take up less space when fused into a solid mass.

These siliceous nodules resemble the nodules of iron-stone mentioned in

note on Canto II. l. 183, in respect to their possessing a great number

of concentric spheres coloured generally with iron, but they differ in

this circumstance, that the concentric spheres generally obey the form

of the external crust, and in their not possessing a chalybeate nucleus.

The stalactites formed on the roofs of caverns are often coloured in

concentric strata, by their coats being spread over each other at

different times; and some of them, as the cupreous ones, possess great

beauty from this formation; but as these are necessarily more or less of

a cylindrical or conic form, the nodules or globular flints above

described cannot have been constructed in this manner. To what law of

nature then is to be referred the production of such numerous concentric

spheres? I suspect to the law of congelation.

When salt and water are exposed to severe frosty air, the salt is said

to be precipitated as the water freezes; that is, as the heat, in which

it was dissolved, is withdrawn; where the experiment is tried in a bowl

or bason, this may be true, as the surface freezes first, and the salt

is found at the bottom. But in a fluid exposed in a thin phial, I found

by experiment, that the extraneous matter previously dissolved by the

heat in the mixture was not simply set at liberty to subside, but was

detruded or pushed backward as the ice was produced. The experiment was

this: about two ounces of a solution of blue vitriol were accidentally

frozen in a thin phial, the glass was cracked and fallen to pieces, the

ice was dissolved, and I found a pillar of blue vitriol standing erect

on the bottom of the broken bottle. Nor is this power of congelation

more extraordinary, than that by its powerful and sudden expansion it

should burst iron shells and coehorns, or throw out the plugs with which

the water was secured in them above one hundred and thirty yards,

according to the experiments at Quebec by Major Williams. Edinb.

Transact. Vol. II. p. 23.

In some siliceous nodules which now lie before me, the external crust

for about the tenth of an inch consists of white agate, in others it is

much thinner, and in some much thicker; corresponding with this crust

there are from twenty to thirty superincumbent strata, of alternately

darker and lighter colour; whence it appears, that the external crust as

it cooled or froze, propelled from it the iron or manganese which was

dissolved in it; this receded till it had formed an arch or vault strong

enough to resist its further protrusion; then the next inner sphere or

stratum as it cooled or froze, propelled forwards its colouring matter

in the same manner, till another arch or sphere produced sufficient

resistance to this frigoriscent expulsion. Some of them have detruded

their colouring matter quite to the centre, the rings continuing to

become darker as they are nearer it; in others the chalybeate arch seems

to have stopped half an inch from the centre, and become thicker by

having attracted to itself the irony matter from the white nucleus,

owing probably to its cooling less precipitately in the central parts

than at the surface of the pebble.

A similar detrusion of a marly matter in circular arches or vaults

obtains in the salt mines in Cheshire; from whence Dr. Hutton very

ingeniously concludes, that the salt must have been liquified by heat;

which would seem to be much confirmed by the above theory. Edinb.

Transact. Vol. I. p. 244.

I cannot conclude this account of Scots-pebbles without observing that

some of them on being sawed longitudinally asunder, seem still to

possess some vestiges of the cylindrical organization of vegetables;

others possess a nucleus of white agate much resembling some bulbous

roots with their concentric coats, or the knots in elm-roots or crab-

trees; some of these I suppose were formed in the manner above

explained, during the congelation of masses of melted flint and iron;

others may have been formed from a vegetable nucleus, and retain some

vestiges of the organization of the plant.