EQU 
EQUINOX, the time when the sun en- 
ters either of the equinoctial points, where 
the ecliptic intersects the equinoctial. It 
was evidently an important problem in 
practical astronomy, to determine the exact 
moment of the sun’s occupying these sta- 
tions; fpr it was natural to compute the 
course of the year from that moment. 
Accordingly this has been the leading pro- 
blem in the astronomy of all nations. It is 
susceptible of considerable precision, with- 
out any apparatus of instruments. It is 
only necessary to observe the sun’s decli- 
nation on the noon of two or three days 
before and after the equinoctial day. On 
two consecutive days of this number, his 
declination must have changed from north 
to south, or from south to north. If his 
declination on one day was observed to be 
21 north, and on the next 5' south, it fol- 
lows that his declination was nothing, or 
that he was in the equinoctial point about 
23 minutes after 7 in the morning of the 
second day. Knowing the precise mo- 
ments, and knowing the rate of the sun’s 
motion in the ecliptic, it is easy to ascertain 
the precise point of the ecliptic in which 
fche equator intersected it. By a series of 
such observations made at Alexandria, be- 
tween the years 161 and 127 before Christ, 
Hipparchus, the father of our astronomy, 
found that the point of the autumnal equi- 
nox was about six degrees to the eastward 
of the star called spica virginis. Eager to 
determine every thing by multiplied obser- 
vations, he ransacked all the Chaldean, 
Egyptian, and other records, to which his 
travels could procure him access, for obser- 
vations of the same kind ; but he does not 
mention his having found any. He found, 
however, some observations of Aristillus 
and Timochares, made about 150 years 
before. From these it appeared evident 
that the point of the autumnal equinox was 
then about eight degrees east of the same 
star. He discusses these observations with 
great sagacity and rigour : and on their au- 
thority, he asserts that the equinoctial 
points are not fixed in the heavens, but 
move to the westward about a degree in 
75 years, or somewhat less. 
This motion is called the precession of 
the equinoxes, because by it the time and 
place of the sun’s equinoctial station pre- 
cedes the usual calculations : it is fully con- 
firmed by all subsequent observations. In 
1750, the autumnal equinox was observed 
to be 20° 2f westward of spica virginis. 
Supposing the motion to hav e been uniform 
EQU 
during this period of ages, it follows that 
the annual precession is about 50 ' J ; that 
is, if the celestial equator cuts the ecliptic 
in a particular point on any day of this 
year, it will on the same day of the follow- 
ing year, cut it in a point 50 ' -> to the west 
of it, and the sun will come to the equinox 
20' 23" before he has completed his round 
of the heavens. Thus the equinoctial, or 
tropical year, or true year of seasons, is 
so much shorter than the revolution of the 
sun or the sidereal year. It is this disco- 
very that has chiefly immortalized the name 
of Hipparchus, though it must be acknow- 
ledged that all his astronomical researches 
have been conducted with the same saga- 
city and intelligence. It was natural, there- 
fore, for him to value himself highly for the 
discovery. It must be acknowledged to 
be one of the most singular that has been 
made, that the revolution of the whole 
heavens should not be stable, but its axis 
continually changing. For it must be ob- 
served, that since the equator changes its 
position, and the equator is only an imagi- 
nary circle, equidistant from the two poles, 
or extremities ot the axis, these poles, and 
this axis must equally change their positions. 
The equinoctial points make a complete 
revolution in about 25,745 years, the equa- 
tor being all the while inclined to the eclip- 
tic in nearly the same angle. Therefore 
the poles of this diurnal revolution must 
describe a circle round the poles of the 
ecliptic, at the distance of about 23 -i de- 
grees in 25,745 years ; and in the time of 
Timochares, the north pole of the heavens 
must have been 30 degrees eastward of 
where it now is. 
EQUITY, quasi (Equalities, is generally 
understood in law, a liberal correction, or 
qualification of the law, where it is too 
strict, too confined, or severe, and is some- 
times applied, where, by the words of a 
statute, a case does not fall within it, yet 
being within the mischief, the judges, by 
an equitable construction, have extended 
its application to that case. Equity is un- 
derstood as a correction of the law : the 
difference between courts of equity and 
law is known only in this country, and 
arises principally, if not entirely, from the 
ditferent modes of trial which must ever 
render them essentially distinct. For it is 
obvious, that where men form contracts in 
the ordinary course of law, the legal conse- 
quence, and the enforcement of them, must 
be, according to general rules, applicable 
to general cases; and the nature of our 
