The Botanic Garden

E >> Erasmus Darwin >> The Botanic Garden

Pages:
1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | 24 | 25 | 26 | 27 | 28 | 29

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. Traite 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.

Pages:
1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | 24 | 25 | 26 | 27 | 28 | 29