ABE 
Abaft the beam , denotes the relative 
situation of any object with the ship, when 
the object is placed in any part of that arch 
of the horizon which is contained between 
a line at right angles with the keel, and that 
point of the compass which is directly op- 
posite the ship’s course. 
ABAS, a weight used in Persia for weigh- 
ing pearls, being one-eighth part lighter 
than the European carat. 
ABASED, in heraldry, is said of the 
wings of eagles, &c. when the tip looks 
downwards to the point of the shield, or 
when the wings are shut; the natural way 
of bearing them being spread. 
ABATE, in law, signifies to break down 
or destroy, as to abate a nuisance, and to 
abate a castle. It means to defeat and 
overthrow, on account of some error or ex- 
ception. 
ABATEMENT, in heraldry, something 
added to a coat of arms, in order to lessen 
its true dignity, and point out some imper- 
fection or stain in the character of the per- 
son who bears it. 
Abatement, in law, signifies the reject- 
ing a suit, on account of some fault either 
in the matter, or proceeding. Hence, plea 
in abatement is some exception alleged, 
and proved, against the plaintiff’s writ, de- 
claration, &c. and praying that the plaint 
may abate or cease ; which being granted, 
all writs in the process must begin de novo. 
ABATOR, in law, one who enters into a 
house or lands, void by the death of the last 
possessor, before the true heir ; and thereby 
keeps him out, till he brings the writ intru- 
sione. 
ABDOMEN, in anatomy, the lower part 
of the trunk of the body, reaching from the 
thorax to the bottom of the pelvis. See 
Anatomy. 
ABDOMINALES, in natural history, an 
order of fishes, having ventral fins placed 
behind the pectoral in the abdomen, and 
the branchia ossiculated. This order com- 
prehends sixteen genera, viz. 
Amia Cobitis Atherina 
Clupea Esox Cyprinus 
Elops Loricaria Exocoetus 
Fistularia Salmo Mugil 
Polynemas Teuthis Silurus 
Argentina 
ABDUCTOR, or Abducent, in ana- 
tomy, a name given to several muscles on 
account of their serving to withdraw, open, 
or pull back the parts to which they are 
fixed. See Anatomy. 
ABERRATION, in astronomy, an ap- 
ABE 
parent motion of the heavenly bodies, pro- 
duced by the progressive motion of light 
and the earth’s annual motion in her orbit. 
Since light proceeds always in right lines, 
when its motion is perfectly undisturbed, if 
a fine tube were placed so as to receive a 
ray of light, passing exactly through its axis 
when at rest, and then, remaining in the 
same direction, were moved transversely 
with great velocity, it is evident that the 
side of the tube wonld strike against the 
ray of light in its passage, and that, in order 
to retain it in the axis, the tube must be in- 
clined, in the same manner as if the light, 
instead of coming in its actual direction, had 
also a transverse motion in a direction con- 
trary to that of the tube. The axis of a 
telescope, or even of the eye, may be con- 
sidered as resembling such a tube, the pas- 
sage of the light through the refracting sub- 
stances not altering the necessary inclina- 
tion of the axis. In various parts of the 
earth’s orbit, the aberration of any one star 
must be different in quantity and in direc- 
tion ; it never exceeds 20" each way, and 
therefore insensible in common observations. 
If AB and AC (Plate Acoustics, &c. fig. 1 ,) 
represent the comparative velocity of light 
and of the earth, in their respective direc- 
tions, a telescope must be placed in the di- 
rection BC in order to see the star D, and 
the, star will appear at E. This discovery 
was made by Dr. Bradley, in his observa- 
tions to determine the annual parallax of the 
fixed stars, or that which arises from the 
motion of the earth in its orbit round the 
sun. 
Aberration of the planets, is equal to 
the geocentric motion of the planet, the 
space whiph it appears to move, as seen 
from the earth, during the time that light 
employs in passing from the planet to the 
earth. Thus with regard to the sun, the 
aberration in longitude is constantly 20", 
which is the space moved by the earth in 
the time 8'v?", which is the time that 
light takes to pass from the sun to the earth. 
Hence the distance of the planet from the 
earth being known, it will be, as the dis- 
tance of the sun is to the distance of the 
planet, so is 8' 7" to the time of light pass- 
ing from the planet to the earth; then com- 
puting the planet’s geocentric motion in 
this time, will give the aberration of the 
planet, whether it be in longitude, latitude, 
right ascension, or declination. The aber- 
ration will be greatest in longitude, and but 
very small in latitude, because the planets 
deviate very little from the plane of the 
