AST 
t;om amount to many thousands, forming a 
beautiful net-work. Its colour is sometimes 
pale or reddish white, sometimes brown. 
ASTERISM, in astronomy, the same 
with constellation. See Constellation. 
ASTEROIDS, in astronomy, a name 
given by Dr. Herschell to the new planets, 
Ceres, Juno, Pallas, and Vesta, lately dis- 
covered ; and which he defines as celestial 
bodies, which move in orbits either of little 
or of considerable eccentricity round the 
sun, the plane of which may be inclined to 
the ecliptic in any angle whatsoever. This 
motion may be direct or retrograde ; and 
they may or may not have considerable at- 
mospheres, very small comas, disks, or nu- 
clei. According to the definitions which 
lie premises, planets are celestial bodies of 
a considerable size and small eccentricity 
of orbit, moving in planes that do not de- 
viate many degrees from that of the earth, 
in a direct course, and in orbits at consi- 
derable distances from each other, with at- 
mospheres of considerable extent ; but bear- 
ing hardly any sensible proportion to their 
diameters, and having satellites or rings : 
and comets are very small celestial bodies, 
moving in directions wholly undetermined, 
and in very eccentric or apparently parabo- 
lic orbits, situated in every variety of posi- 
tion, and having very extensive atmo- 
spheres. Dr. Herschell having compared 
the newly discovered stars by the criteria 
introduced in the above definitions, main- 
tains, that they differ in so many respects 
from both planets and comets, as to war- 
rant his not referring them to either of these 
two classes. 
ASTHMA, in medicine, a painful, diffi- 
cult, and laborious respiration. See Medi- 
cine. 
A ST REV in astronomy, the same with 
Virgo. See Virgo. 
ASTRAGAL, in architecture, a little 
round moulding, in form of a ring, servin'* 
as an ornament at the tops and bottoms of 
columns. See Architecture. 
Astrag \l, in gunnery, a round mould- 
ing encompassing a cannon, about half a 
foot from its mouth. 
ASTRAGALUS, milk vetch, in botany, 
a genus of the Diaaelphia Decandria class 
of plants, with a papilionaceous flower, and 
bilocular-podded fruit, containing kidney- 
like seeds. There are upwards of 60 spe- 
cies ; all of which may be raised from seeds. 
They are in general hardy, and require no 
AST 
other care, but to draw the plants out when 
they come up too thick, leaving them at 
least eighteen inches asunder. 
Astragalus, in anatomy, called also the 
talus, is the superior and first bone of the 
foot, according to its natural situation and 
connection with the leg, being articulated 
with the tibia and fibula, and with the cal- 
caneuin; having its head formed for the ar- 
ticulation with the os navieulare. 
ASTRAL, something belonging to, or 
connected with the stars : thus, astral year 
is the same with siderial year. 
astrantia, black master-wort, in bo- 
tany, a genus of umbelliferous plants, be- 
longing to the Pentandria Digynia class of 
Linnaeus, the flower of which is rosaceous, 
and collected into a sort of head ; and its 
fruit is oval, obtuse, coronated, and stri- 
ated. 
ASTROLABE, an instrument for tak- 
ing the altitude of the sun or stars at sea, 
being a large brass ring, the limb of which, or 
a convenient part thereof, is divided into de- 
grees and minutes, with a moveable index, 
which turns upon the centre, and turns two 
sights : at the zenith is a ring to hang it by in 
time of observation, when you need only 
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, espcciaiiv between 
the tropics, when the sun comes near the 
zenith, and in calm weather. 
ASTROLOGY, a conjectural and truly 
absurd science, which teaches to judge of 
the effects and influences of the stars, and 
to foretel future events by the situation and 
diffeient aspects of the heavenly bodies. It 
may be divided into two branches, natural 
and judiciary ; the fonper being the predic- 
tion of natural effects, as the changes of 
weather, winds, storms, hurricanes, thun- 
der, floods, earthquakes, &rc. and the latter, 
that which pretends to foretel moral events, 
or such as have a dependance on the free- 
dom of the will. 
AS 1 RON 1UM, in botany, a genus of the 
Dioecia Pentandria class 'and order of 
plants. The essential character is, male 
calyx five-leaved ; corol five-petailed. Fe- 
male, calyx five-leaved; corol five-petailed; 
styles tln ee, and one seed. There is but 
one species, the A. graveolens, an upright 
