GEOGRAPHY. 355 
ffr'ifliiefs, 1 here are feveral climates, or difFerent degrees 
of liglit or tcm})erature, in the breadth of one zone. 
Eacli climate o ly difl'ers from its contiguous ones, in 
that tile longed day in fuinmer is longer or fliorter, by 
lialt an hour, for inftance, in the one place than in the 
Other. 
As the climates commence at the equator, at the be¬ 
ginning of the firfi; climate, that is at the equator, the 
day is jud twelve hours long ; but at the end of it, or 
at the beginning of tlie fecond climate, the longed day is 
twelve hours and a half long; and at the end of the 2d 
or beginning of the third climate, the longed day is thirteen 
liours long j and i'o of the red, as far as the polar cir¬ 
cles, where the hour climates terminate, and month 
climates commence. And as an hour climate is a fpace 
comprifed between two parallels of the equator, in the 
fird of which the longed day exceeds that in the latter 
by hall an hour; fo the month climate is a fpace con¬ 
tained between two circles parallel to the polar circles, 
and having its longelt day longer or diorter than tiuit of 
its contiguous one, by a month, or thirty days. But 
many autliors, as Ricciolus, &c. make the longed day 
of the contiguous climates to differ by half hours, to 
about the latitude of 45 degrees; then to did’er by an 
hour, or fometimes two hours, to the polar circle ; and 
after that by a month each. 
The ancients, who cotifined the-climates to ivhat they 
thought the habitable parts of the earth, reckoned only 
feven, the middles of which they made to p)afs through 
fome remarkable places ; as the fird through Meroe, the 
fecond through Sienna, the third through Alexandria, 
the fourth through Rhodes, the fifth through Rome, 
the fixth through Pontus, and the feventh through the 
mouth of the Borydhenes. But the moderns, who have 
failed farther toward the poles, make thirty climates on 
each fide. Commonly the term climate is bedowed on 
any country or region didering from another either in 
relpetl of the feafons, the quality of the foil, or even 
the manners of the inhabitants; without any regard to 
the length of the longed day. Abulfeda, an Arabic 
author, didinguidies the fird kind of climates by the 
term real climates, and the latter by that of apparent cli¬ 
mates. 
59. The greated didance of the earth or any other 
planet from the fun, is called its aphelion-, its neared 
didance, its perihelion ; the longer axis of the ellipfe is 
called the linea apfidnm ; the aphelion is alfo called the 
Jtimma apfts, and perihelion the ima apfs. 
60. Tlie excentricity of the earth, or any planet, is the 
didance between the fun and the centre of the elliptical 
orbit. 
61. The fun is eight days longer in performing its 
apparent courfe through the fix nortliern figns, than 
through the fix fouthern figns.—While the fun appears 
to pals through the northern figns, the earth pafi'es 
through more than half of its orbit ; and while the 
fun appears to pafs through the foutliern figns, tlie 
earth paffes through lefs than half of its orbit. There¬ 
fore, if the velocity of the motion of the earth were 
uniform, the fun mud appear to be longer in palling 
through the fix northern than the fix fouthern figns. 
But whild the earth is pading through the greater part 
of its orbit, it is farther from the fun, and confequently 
moves flower than in the lelfer part. On both thefe 
accounts, the fun’s apparent morion is flower in the 
( northern figns titan the fouthern: the difference is 
found by obfervation to be about eight days. 
62. 1 he apparent' diameter of the fun is greater in 
winter than fummer..—ft is found by obfervation, that 
the diameter of the fun in v,/inler is 32' 47" ; in lum- 
mer, 31'40". And his mean apparent diameter is 32' 12", 
according to fir Ifaac Nevyton, in his Th.eory of the 
Moon, ifence it appears, mat the earth, at the winter 
foldice, or Capricorn, is in its perihelion. The diffe¬ 
rence between fummer and ■winter in the degrees of 
heat, is owing chiefly to tlie different heights to-which 
the fa'll rifes ab'ive the liorizon, and the difierent lengths 
of the days. When ihe fun rifes highelly in fummer, 
its rays fall lefs obliquely, an.;l confequently more of 
them fill on the earth’s furface than in winter; and 
wlien the days are long, and the nigiits (liort, the earth 
and air are more heated in tiie day than they are cooled 
in the night, and the reverie. 
To illuftrate more obvioully th.e principles of matlie- 
matical geography above laid down, it will here be ne- 
celfary to call in the aid of the armillary fphere, and of 
the terrefirial and celcftial globes', which lire calculated 
to imprefs on the mind the nature and ufc of thole great 
circles which aflronomers and geographers have fup- 
pofed to exill in the concave fphere of the heavens, and 
over the convex fphere of the earth, for the purpofe of 
inveftigating w’ith accuracy' and precilion the various 
phenomena applicable to both. 
Of the armillary SPHERE. 
This is an artificial inftrument, calculated to repre- 
fent, by its real circles, thofe imaginary ones w'h.ich we 
have above deferibed as dividing the heavens and the 
earth into various difiindl: parts. So that if the eye 
could be placed in the centre of this fphere, we Ihould 
fee its circles upon or againll thofe very points of the 
heavens where the imaginary circles above-mentioned 
are fuppofed to be fituated. It is called armillary, be- 
caufe it confilts of a number of rings of brafs, called 
by the Latins armillre, from their refembling bracelets 
or rings for the arms. The fix great circles of th.e 
fphere require particular attention : viz. the horizon, 
the meridian, the equator, the ecliptic, the equinoctial 
colure, and the folfiitial colure. The fphere is fufiained 
in a frame, on the top of which is a broad circle repre- 
fenting the horizon. On the infide of the horizon are 
two notches for receiving a llrong brafs circle, w'hich 
repr.efents the meridian. It is fufpended on tv/o pins, 
at two oppofite points of the meridian ; thefe pins are 
a continuation of the axis of the fphere both ways; 
and as the fphere turns round upon tltem, they are con- 
fidered as poles ; one the north, the other the fouth, pole. - 
The equator is th.at circle which goes round the fphere 
exadlly'in the middle, between the two poles.—The 
ecliptic is that circle which croffes the equator obliquely ; 
it is divided into twelve equal parts, each of which con. 
fifts of thirty degrees.—1 he ecpdnoclial colure is the great 
circle which paffes through thofe two points of the 
equator that are intercepted by the ecliptic.—The^/o/- 
Jlitial colure is the other great circle at right angles to 
the equator. 
There are alfo four lelfer circles in the fphere, two 
tropics, and two polar circles ; tlicfe are all parallel to 
the equator .—The tropic of Cancer is the parallel, which 
is on the north fide of the equator ; and the tropic of Ca¬ 
pricorn is liiuated on the fouth fide of the equator. ^ he 
two polar circles are at the lame difrance from the two 
poles, as the tropics are from the equator ; that towards 
the north pole is Che arElk circle, tliat towards the fouth 
pole the antarElic circle. “ / 
The armillary fphere is corredHy reprefented in the 
Geography Plate I. fig. i. The broad circle, HO, is 
the horizon, becaule it terminates the vievv of the Ipec- 
tator, dividing the fpher'e into two equal parts ; that 
called the villble hemilphere, and that, below, the 
invifible hemilphere. When the fun, moon, &c. de- 
feend below this circle, we fay, they arc fef, when they 
appear above it, we fay, they have rijeti. On the broad 
circle, reprefenting the liorizon, are marked the thirty- 
two points of the mariner’s compafs'; in which the ealt, 
welt, north, and fouth, points, are called cardinal points-. 
Tiie large brafs circle, MR, reprefents the general 
meridian, bccaufe. it ferves to reprefent any particular 
meridian ; for as it is fixed, and the fphere is move¬ 
able about its axis, vve can, by turning the fph.ere, 
bring 
