Mathemati- 
cal Geogra- 
ye 
— 
Properties 
of the globe 
as illustra- 
tive of ma- 
thematical 
geography. 
General de- 
scription of 
the terrestri- 
al globe. 
154 
its motion and various positions, by means of an artifi- 
cial sphere. We find, accordingly, that from a very 
early peviod, the globe, with certain modifications, has 
been made use of for this purpose, and notwithstanding 
all the discoveries and improvements in the astronomi- 
cal apparatus of modern times, it still continues to af- 
ford the-simplest, and at the same time a correct illus- 
tration, of the principles of mathematical aphy. 
We have already seen in what way, and to what extent, 
the earth differs in figure from a true sphere, and how 
imperceptibly small the irregularities of its surfage be- 
come, when represented on a sphere six or seven feet 
in diameter. If the sphere be reduced to one-third of 
this, which is more nearly the size of ordinary globes, 
these irregularities will totally disappear, and the diffe- 
rence between the polar and equatorial diameters, or 
between the meridian and equator, be itself inappreci- 
able. The earth therefore, with all its inequalities, 
can alone be represented by a sphere ; and the only re- 
maining question is, how can the instrument be accu- 
rately constructed, and most extensively applied ? 
In constructing an artificial sphere or globe, the first 
operation is to prepare a spherical body of wood, metal, 
ivory, or such other substance as may be found most 
convenient. The materials commonly employed, and 
perhaps upon the whole best adapted for this purpose, 
are paper and plaster, prepared and combined by the 
following process: On a spherical block or mould of 
wood, somewhat less than the size of the intended 
globe, are laid successive coverings. of paper or paste- 
hoard, attached to one another by glue or paste, till 
the whole is about the thickness of 4,th or ths of an 
inch. When completely dry, this covering is cut into 
two hemispheres, by which it is. separated from the 
mould ; and the hemispheres being again placed on 
a wooden axis, previously prepared for the polar 
diameter of the globe, they are stitched together in the 
same position, as when attached to the block or mould. 
In the extremities of the wooden axis, are fixed pins of 
iron or other metal, which represent the poles, and by 
which the globe is suspended in a metallic semicircle, 
whose diameter is exactly equal to that of the intended 
obe. In this state, a composition of whiting and glue 
is applied to the surface of the paper, the globe in the 
mean time being made to revolve, so that the interior 
edge of the semicircle, which is prepared for the pur- 
pose, pares off the superfluous plaster from the pro- 
jecting parts of the surface. The whole being thus 
made perfectly smooth and spherical, and at the same 
time equally balanced on its axis, so as to remain in 
any position in which it may be placed while suspend- 
ed by the poles, it is set aside to dry and harden, 
when it is ready to receive the various circles which 
aphers have imagined to be described on the sur- 
face of the earth, and which we have already explained, 
viz, the equator, ecliptic, meridians, the tropics, polar 
circles, and other parallels of latitude. These circles 
being described by some of the methods afterwards to be 
explained, the various parts of the surface of the earth 
are then delineated, according to their actual situation, 
the position of every place being determined by the in« 
tersection of its meridian and parallel of latitude. The 
iron pins in the extremities of the axis, formerly used 
for fixing the globe in the metallic semicircle, for the 
purpose of applying the plaster, are now employed 
to suspend it in a brass circle, of such a diameter 
that the globe may revolve easily without coming in 
contact with any part of its interior edge. ‘This ring is 
called the universal meridian, because by the revolution 
GEOGRAPHY. | 
of the globe, it may be made to represent the meridian Mat 
of any place. The frame in which the globe is placed °! © 
is variously constructed, according to the taste and 
fancy of the workman ; but its top or upper part al- ~~ ¥ 
ways consists of a broad horizontal circle of wood or 
metal WNES, (Fig. 4.) of which the interior diameter 
WE is equal to the interior diameter of the brazen me- Pi 
CCLX 
ridian. The latter, with the globe su ed in it, Fig. 
passes through notches at N .and §S, rests by its 
under edge in a groove in which it may be made to 
slide, so as to elevate or depress the pole at pleasure. 
In every position, however, one half of the globe is 
above, and another below the surface of WNES, which 
is therefore taken to represent the rational horizon. On 
the surface of this horizontal rim are described several 
concentric circles, variously divided, according to the 
purposes which they are intended to serve. ‘The lar- 
gest, or that towards the outer edge, is named the ca- 
lendar, being divided into 365 parts, representing the 
days of the year, classed under their sespeetive months, 
The next represents the septic. dips inkp Sans Ane 
degrees, and, so arranged that int ipti 
wanes opposite to the day on which the sun ae 
point. The names or characters of the different signs 
are placed at the beginning, or opposite the middle of 
each, The innermost circle the horizon di- 
vided into quadrants, two of these being reckoned from 
W the west point, and the other two from E the east 
point, towards N and S, the north and south points. 
This circle, or rather another concentric with it, but 
larger, is divided into $2 equal parts, representing the 
points or rhumbs of the mariner’s compass. The side 
of the brazen meridian facing the west is divided into ° 
degrees, or if the size of the circle will admit into 
degrees and minutes, reckoning from the equator ‘to- 
wards both poles on two quadrants, and from the 
towards the equator on the other two, each quadrant 
being numbered from 1 to 90. The eircle t- 
ing the equator is also divided into degrees in two di- 
rections, on each side of the first meridian, which, on 
British globes, is that of Greenwich. The 15th, 30th, 
45th, &c. degrees towards the west are marked I. IT. 
III. &c. to facilitate the conversion of longitude, and 
difference of longitude into time, and the contrary. The 
ecliptic, which is generally made to intersect the equa- 
tor and first meridian in the same point, is divided into 
12 signs, each sign being again subdivided into 30 de- 
grees, and reckoned from the first meridian eastward. 
The characters of the signs are placed at the beginning, 
or opposite the middle of each, as on the horizon. 
Such is a general view of the artificial sphere usually 
employed to represent the earth. It is called the ter~ 
restrial globe, to distinguish it from that used to repre- 
sent the heavens, and which is denominated the celestial = 
globe. The latter, like the terrestrial globe, is suspend- Celesti 
ed by the poles in a brazen or universal meridian, and 8!°>% 
mounted in the same way in ahorizon. On its surface 
are described the equinoctial, the ecliptic, the tropics, 
the ENS circles, the equinoctial and solstitial colures, 
circles of celestial longitude, and parallels of celestial 
latitude. As the celestial sphere revolves from east to 
west, the graduation of the en meridian is towards 
the east, but, in other respects it is the same as that of 
the terrestrial globe. The ecliptic is divided in the 
same way as on the other globe, but te each de- 
gree is a dot, representing the day on which the sun is 
at that point, The degrees of the equator are reckoned 
in one direction only, viz. towards the east, and the 
equinoctial and solstitial points are determined from . 
