GEOGRAPHY. 
declination of the fun for every day in the year may be 
found, and a table conftrudted. 
18. The ecliptic being divided into twelve equal 
parts, each of thefe parts is called a fign ; and the names 
of the figns in the ecliptic are the fame with thofe in 
the zodiac, as ftated in article i6, but A) not exa6tly 
correfpond with them. 
19. The two points in which the ecliptic cuts the 
equator, are called the equinoElialpoints: the vernal equi¬ 
nox is at the firft degree of Aries in the ecliptic ; the 
autumnal, at the firft of Libra.—The moment of time 
in which the fun enters the equator, may be found by 
obfervation, the latitude of the place of the obferver 
being known. For in the equinoftial day, or near it, 
with an inftrument exactly divided into degrees, minutes, 
and parts of minutes, take the meridian altitude of the 
fun : if it be equal to the altitude of the equator, or to 
the complement of the latitude, the fun is then in the 
equator j but if it is not equal, mark the difference, 
which will be the declination of the fun. The next day, 
again obferve the meridian altitude of the fun, and ga¬ 
ther from thence his declination. If thefe two declina¬ 
tions be of different kinds, as the one fouth and the other 
nortli, the equinox happens feme time between the two 
obfervations; if they be both of the fame fort, tlie fun 
has either not entered the eqiiinodtial, or has palfed it. 
And from thefe two obfervations of the fun’s declina¬ 
tion, the moment of the equinox may be inveftigated.— 
See Astronomy, vol. ii. p. 370-373. 
20. The points of the ecliptic which are at the great- 
eft diftance trom the equator, are called the foljlices ; and 
the circles which pafs through thefe points parallel to 
the equator, are called the tropics : the fuinmer folftice 
is at the firft of Cancer, the winter folftice at the firft of 
Capricorn: the northern tropic is called the tropic of 
Cancer, the fouthern of Capricorn. The fun is once 
in the year at each of the tropics, and tw'ice at the 
equator. 
21. Circles which pafs through the poles at right 
angles to the equator, or any other great circle, are called 
Jecondaries to that circle: the lecondary which pafles 
through the equinodtial points, is called the equinoSial 
colure. 
22. That pole which is neareft the tropic of Cancer is 
called the north pole •, that which is neareft the tropic of 
Capricorn, is called fouth pole. 
23. An imaginary line palling through the centre of 
the ecliptic, and perpendicular to the plane of it, is the 
axis of the ecliptic : its extremities are the poles of the eclip¬ 
tic, and all circles, palling through thefe poles, and per¬ 
pendicular to the ecliptic, are its fecondaries. The axis 
of the ecliptic makes an angle of 23^ degrees nearly 
with that of the equator. 
24. The polar circles are deferibed by the revolution 
ot the poles of the ecliptic about the poles of the equa¬ 
tor: that which is next to the north pole, is called the 
crff/c circle 5 the oppofite, the a«ra)-<f 7 fr circle. 
25. The declination of any heavenly body, is its diftance 
from the equator; this is either northern, or fouthern. 
1 he degrees of declination of any body are reckoned 
upon a fecondary of the equator palling through that 
body. 
26. The right afeenfon of any heavenly body, is its diftance 
from the fiift of Aries reckoned upon the equator; this 
is meafured, by obferving the arc which is intercepted 
between Aries and a lecondary to the equator pafling 
through the fun or ftar. 
27. The latitude of any heavenly body, is its diftance from 
the ecliptic ; and the degrees of latitude are reckoned on 
a lecondary of the ecliptic palling through the body. 
28. The longitude of any heavenly body is its diftance from 
the firft of Aries ; and is meafured on the ecliptic by the 
are intercepted between the firft of Aries and the fecon¬ 
dary of the ecliptic which paffes through the body : the 
longitude increafes, as the body recedes from Aries, 
551 
through the whole revolution, til] it reaches 360°, or 
comes again to Aries. 
29. Two bodies are faid to be in conjunEiion w’ith each 
other, when they have the fame longitude, or are in the 
fame fecondary of the ecliptic on the fame fide of the 
heavens, though their latitude be different: they are 
faid to be in oppofition, when their longitudes differ half 
a circle, or they are on oppofite lides of the heavens. 
30. The axis of the heavens is perpendicular to the 
planed of all the circles which the heavenly bodies de- 
fcrib(t in their apparent diurnal motions. For the hea¬ 
venly bodies, from the revolution of the earth round its 
axis, appear to move from eaft to w^eft in circles perpen¬ 
dicular to the axis. The planes of all thefe circles are 
parallel to the equator; and the axis paffes through the 
centres of the circles. 
3r. The celeftial fphere is called right, oblique, or pa¬ 
rallel, as the celeftial equator is at right angles, oblique, 
or parallel, to the horizon. 
32. In all places on the equator, the poles lie in the 
horizon, and all the circles of daily motion make right 
angles with the horizon.—For thefe places having no 
latitude, the poles are neither elevated above, nor de- 
prelfed below, the horizon ; and fince the equator is 90 
degrees from the poles, it is at right angles to the hori¬ 
zon, and alfo all circles parallel to it. 
33. Thofe who live at the equator are in a right 
fphere ; and, confequently, their days and nights are al¬ 
ways equal. The great circle of the celeftial equator 
and its parallels, make right angles with the horizons of 
all places in the earth’s equator; therefore the inhabi- 
tants of thofe places live in a right fphere. Hence, be- 
caufe the celeftial axis P T S, Plate II. fig. 3, is in the 
plane of their horizon, and becaufe this axis is at right 
angles to the plane of the equator, and pall'es through 
its centre, and through that of all circles parallel to the 
equator, the plane of the horizon alfo paffes through 
the centres of thefe circles; and confequently divides 
the equator and its parallels into two equal parts. One 
half of thefe circles will therefore always be above the 
horizon, and the other half below it. But each of the 
heavenly bodies in th.eir daily motion deferibes feme one 
of thofe circles, and the diurnal motion of the earth is 
uniform ; therefore any heavenly body will, in this fitua- 
tion, be juft as long above the horizon as belov/ it. And 
becaufe this will be the cafe with refpeit to the fun, as 
well as any other body, in whatever part of the heavens 
he is feen, the days and nights at the equator will always 
be of equal length.—See Astronomy, vol. ii. p. 369. 
34. At the poles of the earth, one celeftial pole is in 
the zenith, and the other in the nadir; the equator co¬ 
incides with the horizon, and all the circles of daily mo¬ 
tion are parallel to the horizon.—For the latitude of the 
poles is 90 degrees from the equator, and the circles of 
daily motion are parallel to the equator. 
35. Thofe who live at either pole are in a parallel 
fphere ; they fee the heavenly bodies carried round them 
in circles parallel to the horizon; and their day and 
their night, continues eacli half a year. An inhabitant 
at P, Plate 11 . fig. 3, has the equator E Q^in the hori¬ 
zon, and all its parallel circles are parallel to the hori-. 
zon. Therefore each of the heavenly bodies, in its ap¬ 
parent daily motion, being in fome one of thefe circles, 
muft deferibe a path parallel to the horizon: fo that 
thole which are above the horizon will never fet by this 
motion, and thole which are below it will never rife. 
The fun, therefore, in this place, will not rife or fet 
by the diurnal motion of the earth. But from the an¬ 
nual motion of the earth, the fun daily changes its ap¬ 
parent place in the heavens, till it lias deferibed the 
circle of the ecliptic, CL; one half of which is above 
the horizon, and the other half below it, becaufe thefe 
circles have their common centre in T, the centre of 
the earth. Therefore, for one half of the year the fun 
will be in fome part of- CT, that half of the ecliptic 
which 
