36a G E O G 
E, fig. 2 , are the poles of the ecliptic, andy/z the eclip¬ 
tic itfelf; and that tl\e polar circles and tropics, with 
the equator and the parallels thereof, are to be de¬ 
termined from their declinations. 
M. de la Lande, in his AJironomii, tom. iii. p. 73'6, de- 
fcribes the following methods. “ To conftriidt celeltial 
and terreftrial globes, gores mufl: be engraved, as fhewn 
in the engraving, at fig. 5. The length PC, the axis of 
this curve, is equal to a quarter of the circumference of 
the globe ; the intervals of the parallels- on the axis P C, 
are all equal, the radii of the circles KD I, which re- 
prefent the parallels, are equal to the co-tangents of the 
latitudes ; and the arches of each, as D I, are nearly equal 
to the number of the degrees ,of the breadth of the gore 
(which is ufually 30°) multiplied by the fine of the lati¬ 
tude; thus there will be found- no intricacy in tracing 
tliem ,• but the difficulty proceeds from the variation 
found in the trial of the gores when patting them on the 
globe, and of the quantity that mutt be taken from the 
paper, lefs on the tides than in the middle (becaufe the 
pdes are longer), to apply it exactly to the fpace that 
it fliould cover, 
“ The method ufed among workmen to delineate tlie 
gores, defcribed in the 7th vol. of the Encyclopedie, is little 
geometrical, though fufficient in practice. Draw on the 
paper, as at fig. 3, the line A‘C, equal to the chord of 
15°, to make the half breadth of the gore ; and a per¬ 
pendicular PC, equal to three times the chord of 30”, 
to make tlie half length: for thefe papers, the dimen- 
fions of which will be equal to the chords, become equal 
to the arcs themfelves when they are palled on the globe. 
Divide the height C P into nine parts, if the parallels 
are to be drawn in every 10° ; divide alfo the quadrant 
B E into nine equal parts through each divilion point of 
tlie quadrant, as G ; and through the correfponding point 
D ot the right line C P draw the perpendiculars H G F 
and D F, the meeting of which in F gives one of the 
points of tlie curve B EP, w'hich will terminate the cir¬ 
cumference of the gore. When a fufficient number of 
points are thus, found, trace the outline PIB with a 
curved rule. By this conftruftion are given the gore- 
breadths which are on the globe, in the ratio of the 
cofines of tlie latitudes; fuppofing thefe breadths, taken 
perpendicular to C D, which is not very exaCt (but it is 
impoflible to prefcribe a rigid operation), fufficient to 
make a plane which (hall cover a curved furface, and 
that on a right line A B lhall make lines PA, PC, PB, 
equal among themfelves, as they ought to be on the 
globe. -To defcribe the circle K D I, which is at 30° from 
tlie equator, there muft be taken above D a point, which 
fliall be diftant from it the value of the tangent of 60°, 
taken out eitlicr from the tables, or on a circle equal to 
the circumference of the globe to be traced ; this point 
will lerve as a centre for the parallel DI, which Ihould 
pafs thiougii the point D, for it is fuppofed equal to 
that ot a cone circumfcribing the globe, and which would 
touch at the point D. The meridians may be traced to 
every 10 degrees, by dividing each parallel, as KI, into 
three parts at the points L and M, and drawing from the 
pole P, through all thefe divifion points, curves, which 
reprefent the intermediate meridians between PA and 
P B, (as B R and ST, in fig. 6.) The ecliptic may be 
defcribed by means of the known declination from dif- 
lerent points of the equator that may be found in a table ; 
lor 10”, it is 3° 58'; for 20®, 7° 50' = B Q; for 30°, 
11° 29', &c.” 
It is obferved in general, that the paper on which 
charts are printed, luch as the colombier, Ihortens itielf 
-jJg- part or a line in fix indies upon an average, when it 
is dried after printing; this inconvenience mud there¬ 
fore be corredied in the engraving of the gores : if, not- 
withftanding that, the gores are found too fliort, it mud 
be remedied by taking from the furface of the ball a 
little of the white material with which it is covered, 
R. A P H Y. 
thereby making the dimenfions fiiitable to the gore as it 
was printed. But what is mod fingular is, that in draw¬ 
ing the gore, moidened with the pade to apply on the 
globe, the axis GH, fig. 6, lengthens, and the fide AK 
ffiortens, in fuch a manner, that neither the length of 
the fide A C K nor that of the axis G E H of the gore, 
are exadlly equal to the quarter of the circumference of 
the globe, when compared to the figure on the copper, 
or to the numbered fides fliown in the engraving. Mr. 
Bonne having made feveral experiments on the dimen¬ 
fions that gores take after they had been paded ready 
to apply to tlie globe, and particularly with the paper 
he made ufe of for a globe of one foot in diameter, found 
that it was neceflary to give to the gores on the copper 
the dimenfions fet forth on the left hand fide of fig. 6. 
Suppofing that the radius of the globe contained 720 
parts, the half breadth of the gore is A G = t88-^g, the 
didance AC for the parallel of 10 degrees taken on the 
right line L M is i28’i, the fmall deviation from the 
parallel of 10 degrees in the middle of the gore ED is 4, 
the line A B N is right, the radius of the parallel of 10®, 
or of the circle C E F, is 4083 ; and fo of the others as 
marked in the figure. The fmall part under H, lias its 
radius 253, indead of 274, which it would have if the 
fine of 20° had been the radius of it. 
To projeEl Maps and Charts. —A map is the reprefenta- 
tion of the furface of the earth upon a plane; and thefe 
are tithtr general or particular. A general map, is a map 
of the whole earth, and this is reprefented in two circles 
touching each other, reprefenting two hcmifpheres of 
the earth, the boundaries of which are meridians. A 
particular map, is a map of only a part of the furface of 
the earth, as of one of the quarters of the world, or of 
any particular country. The laying down of tliefe maps 
is called projedlion, of which there are feveral kinds. In 
doing this, three principal things are required : viz. To 
fiiow the latitude and longitude of places; this is done 
by drawing a certain number of meridians, and parallels 
of latitude. The fecond requifite is, to exhibit, as nearly 
as pollible, the fliape of all the countries; for it cannot 
be done accurately by any projeftion, on account of its 
being made on a plane, w hen the earth is globular. The 
third is, to fiiow the bearings of places from each other, 
and their difiances ; the former can be done in one pro- 
jedfion, but the latter cannot. 
The projedtion of maps is made according to the rules 
of perfpedlive. If the eye be fuppofed to view the earth 
from an infinite diftance, the appearance reprefented 
upon a plane i,s called an orthographic projedfion. In this 
cafe, the parts about the middle are' very well repre¬ 
fented, but the extreme parts are very much contradled. 
But the method generally made ufe of by geographers 
for maps, is the Jlereographic, where the eye is fuppofed 
to be on the furface of the earth, and looking at the op- 
pofite hemifphere. There is alfo a very ufeful projec¬ 
tion, cMtdglobular, in which meridians, equidifiant upon 
the furface of tiie earth, are reprefented by equidifiant 
circles in the map. There is alfo another projedtion, 
tiled by navigators, called Mercator's, in which, both 
the meridians and parallels of latitude are reprefented 
by firaight lines. Thefe are called fca charts, wherein - 
are exliibited fome part of the fea, with the Ihores that 
bound it: the inlands are generally omitted, as being 
of no ufe to the failor; but the parts near the Ihore are 
carefully, laid dotvn, with marks lignifying rocks, fands, 
or flats, and figures exprelling the foundings, or depths 
of the water. 
M^'lien we are to delineate a map of d. [mail part of the 
earth, if it be near the equator the meridians and paral¬ 
lels of latitude may be reprefented by equidifiant firaight 
lines. If at fome diftance from the equator, the meri¬ 
dians muft then be made to converge a little, and the 
more fo, the further you recede from the equator. When 
a map is made of a very fmall difiribi, as of a county, on 
whatever 
