AST 
nearly in a similar manner on the simple or 
dead animal fibre as on the living solid ; in 
both cases thickening and hardening : when 
applied to the living solid, they produce in- 
crease of tone and strength, restrain inordi- 
nate actions, and check excessive discharges 
from any vessels or cavities ; and to the dead 
fibre occasion that density, toughness, im- 
perviousness to water in a greater or lesser 
degree, and insusceptibility to the common 
causes of putrefaction, in which consists the 
process of tanning, or preparation of leather, 
bee Tanning. 
ASTRODICTiCUM, an astronomical in- 
strument, by means of which many persons 
are able to view the same star at the same 
time. 
ASTROITES, or star stone, in natural 
history, is so called on account of its resem- 
blance to a star. It is controverted among 
naturalists, whether they are parts of a pe- 
trified marine animal, or; as is more probable, 
a species of coral buried in the earth. The 
corals forming these stars are sometimes 
round, sometimes angular, and their columns 
are sometimes separated, and sometimes the 
striae run into one another. 
ASTROLABE, the name for a stereogra- 
phic projection of the sphere, either upon the 
plane of the equator, the eye being supposed 
to be in the pole of the world ; or upon the 
plane of the meridian, when the eye is sup- 
posed in the point of intersection of the equi- 
noctial and horizon. 
Astrolabe is also an instrument for 
taking the altitude of the sun or stars at sea, 
being a large brass ring, A C B D (Plate IX. 
Miscel. fig. 5.), the limb of which, or a con- 
venient part thereof A C, is divided into 
degrees and minutes, with a moveable index 
F G, which turns upon the centre, and turns 
two sights : at the zenith is a ring A, to hang 
it by in time of observation, when you need 
only to turn the index to the sun, that the 
rays may pass freely through both sights, 
and the edge of the index cuts the altitude 
upon the divided limb. This instrument, 
though not much in use now, if well made, 
and of great weight that it may hang the 
steadier, is as good as most instruments that 
are used at sea for taking altitudes, espe- 
cially between the tropics, when the sun 
comes near the zenith, and in calm weather. 
ASTROLOGY, a conjectural science, 
which absurdly pretended to foretel future 
events by the situation and different aspects 
of the heavenly bodies. 
ASTROLUS, in natural history, a name 
given by authors to a white splendid stone, 
small in size, roundish, and resembling the 
p\?pe rvf nshPS 
' ASTROMETEOROLOGIA, the art of 
foretelling the tveather and its changes from 
the aspect of the moon and stars. This is 
sometimes called meteorological astrology. 
There is however but little reason to believe 
that the heavenly bodies have any great in- 
fluence on our atmosphere. See Meteo- 
rology. 
ASTRONIUM, in botany, a genus of the 
class and order dioecia pentandria. The 
essential character is, male, calyx five-leav- 
ed ; corolla five-petalled ; female, calyx five- 
leaved ; corolla five-petalled ; styles three : 
seed one. 
There is but one species, a tree, a native 
©f New Spain, abounding in a slight gluti- 
A S T 
nous terebinfhine juice, which has a disa- 
greeable smell. 
ASTRONOMICAL place of a star or 
planet, is its longitude or place in the eclip- 
tic, reckoned from the beginning of Aries, 
according to the natural order of the signs. 
ASTRONOMY, is a mixed mathematical 
science, which treats of the heavenly bodies, 
their motions, periods, eclipses, magnitudes, 
&c. and of the causes on which they de- 
pend. 
History of Astronomy . — The origin of 
astronomy is very obscure, and appears 
to be also very antient. “ There is no 
doubt,” says Cassini, (< that astronomy w r as 
known even from the commencement of the 
world. It was not only curiosity which led 
man to the study of astronomy, but it may 
be said that necessity itself obliged him to 
it. For if he did not observe the seasons 
which result from the apparent changes of 
the sun’s place, it would be impossible to 
succeed in the practice of agriculture and 
other useful arts.” But astronomy, even if 
it could be considered as useless to man, de- 
rives from its very nature a certain degree 
of dignity. It is, moreover, upon this that 
navigation, geography, and chronology, de- 
pend. By its aid man passes the seas, and 
penetrates into foreign climes, becomes ac- 
quainted with those which he inhabits, and 
regulates the dates of ages past. 
Hipparchus laid the principal foundation 
of a methodical astronomy, 147 years before 
Christ. When an opportunity was given 
him to observe a new fixed star, he directly 
made a list of such stars, so that in the next 
age they were able to know if one had ap- 
peared more than usual. Ptolemy, about 
280 years afterwards, added his observations 
to those of Plipparchus, and by the na- 
tural advantage which he possessed over his 
predecessor, he was enabled to rectify greatly 
the observations that he had made. 
Astronomy was very much neglected from 
this period till after the middle of the 13th 
century, at which time Alphonsus, king of 
Castile, formed tables more exact than the 
preceding. Indeed, a celebrated astronomer 
having at an early period been sufficiently 
attentive to observe all the planets in one 
night, found not one in the place of another, 
but all according to the tables w hich had been 
made by order of the king of Castile. It 
was not, however, till the 16th century that 
astronomy derived fresh lustre from the 
system of Copernicus, published at Nurem- 
berg in 1543, and brought to perfection by 
Kepler and Galileo ; a system so bold and 
daring, that it produced general astonish- 
ment, and yet its truth has been confirmed 
by the observations of every succeeding age. 
The surface of the heavens seems to us to be 
studded with stars ; between the fixed stars 
and us there seem to be other stars which 
change their situations respectively one to- 
wards another, and these all astronomers 
have agreed in calling planets, or wandering 
stars. The antient philosophers, who knew 
so very little even of the movements of the 
planets, had no evident means to know the 
true disposition of their orbits ; and this is 
the reason that they vary so greatly in their 
opinions. They supposed, at first, the earth 
to be immoveable, as the centre of the uni- 
verse, and that all the celestial bodies turned 
about her; which, indeed, was natural for 
AST 165 
them to believe, without having discussed 
the proofs to the contrary. 
The Babylonians, however, and afterwards 
Pythagoras and his disciples, are said to have 
considered the earth as a planet, and the sun 
as immoveable, and the centre of our plane- 
tary system. Plato was the reviver of the 
system of the immobility of the earth, and 
many philosophers followed his sentiment ; 
among others was Claudius Ptolemy, the 
celebrated astronomer and mathematician of 
Pelusium in Egypt, already mentioned, who 
lived in the beginning of the second cen- 
tury of the Christian aera. It is, however, 
incredible that the true system of the w r orld 
having been once discovered, the hypothesis 
by which the earth is supposed to be the 
centre of the celestial movements should 
have again prevailed ; for though this hypo- 
thesis accords w ith appearances, and seems 
to agree at first with the simplicity of na- 
ture, yet it is impossible on that system to 
account for the celestial movements. Pto- 
lemy, w'ho has given the name to this system, 
endeavours to prove that the Earth is truly 
immoveable as the centre of the universe; 
and he places the other planets round 
about her in the following order, beginning 
by those which he believes the next to the 
Earth ; the Moon, Mercury, Venus, the 
Sun, Mars, Jupiter, and Saturn, till he comes 
at length to the fixed stars. His principal 
reason for placing Mercury and Venus be- 
neath the Sun, though they are often seen 
farther from the Earth than from the Sun, 
w T as, wdthout doubt, because the duration 
of their revolution was shorter than the 
apparent revolution of the Sun. When, 
however, astronomers had begun to observe 
the planets, they remarked that Mercury and 
Venus are sometimes nearer, and some- 
times farther, than we are from the Sun ; 
and that Venus never departs from the 
Sun more than about 47 degrees and a 
half ; and Mercury about 28 degrees and a 
half, and sometimes much less. But it is 
evident that if these two planets turn- 
ed about the Earth, as they suppose the 
Sun himself turned, they w'ould some- 
times appear opposite to the Sun, or far- 
ther from him than 180 degrees, which 
never happens. This is the reason why 
the Egyptians regarded these two planets 
as satellites of the Sun, and thought that they 
turned about liim> their orbits being carried 
with this star in his revolutions about the 
Earth. They therefore supposed the Earth 
immoveable, as the centre of the system; 
and they supposed the other celestial bo- 
dies to turn round her : first, the Moon ; 
secondly, the Sun, about which they made 
Mercury and Venus turn, without ever 
touching the Earth in their revolution, till 
they come to Mars, Jupiter, and to Saturn, 
the wdiole of their movements being deter- 
mined by the fixed stars. 
At the present day, when we know the 
immense distances which separate these stars, 
both of these systems become insupportable,, 
because of the prodigious rapidity which 
they require in the movements of the ce- 
lestial bodies ; for if we take a view of these 
distances,, it will be found necessary for these 
stars to go through the whole course of 
their orbits in about 24 hours, and that the 
Sun should run through, in a second of time* 
more than the space of 2500 leagues. To- 
