other Characters, ufed in this Book.

S the Sign of Equality, and is read equal, as 3
and 25, fignifies 3 and 2 are equal to 5.

Is the Sign of Addition, and is read plus or
more, as 4+2, fignifies 4 more 2, or 2 added to 4,
6.

Is the Sign of Subftraction, and is read minus ór
lefs, as 2 fignifies 9 lefs 2, or 2 fubftracted from
9,7.

--

x Is the Sign of Multiplication, as 4 x 3 fignifies 4

multiplied by 3,

12.

Is the Sign of Divifion, as 12÷÷3 fignifies 12

divided by 3,

=

4.

Degrees are fometimes expreffed by a little Circle

over the right Hand Corner of a Figure, as 50 ftands

for 5 Degrees.

Minutes, by a fingle Stroke, as 5' ftands for 5

Minutes.

Seconds, by z Strokes, as 5" ftands for 5 Seconds.

E R R AT A.

Page 4 in the Marginal Note, Line 5, for from read form. p.

48, 1. 9, for Lays r Degrees. p. 52, 1. 5, from the Bottom, for

foreign Countries, r. moft Countries of Europe. p. 53, l. 14, r.

21st. p. 54, 1. 13, r. 23d. p. 60, 1. 29, r. Equinoctial. p. 63

in the Note, 1.1, for as r. at. p. 79, 1. 15, for but the Moon's

Attraction is much ftronger, r. but is differ nt in different Parts of

it, which Difference is much the most confiderable in the Moon's

Attraction. p. 96, 1, fr taken r. take p. 109, 1. 16, for 4th

15th. p. 141, 1.2, dele And. Appendix, p. 149, 1.4, r. mun-

dane. p. 151, 21. for as was r. was as. p. 156, 1.7, r. Equator.

p. 162, l. 17, for io r. to. in the Index, 1.2, for 143 r. 147.

THE

PART

I

The Doctrine and Ufe of the

GLOBES.

CHAPTER I.

A Defcription of the Globes; particularly of the Terreftrial Globe, its Points and Circles.

GLOBE or Sphere fignifies a round Body, every Part of whofe Surface is equally diftant from its Center.

By THE GLOBES, which we are now to treat of, we mean two fuch artificial spherical Bodies, one of which is fuppofed to represent the Earth, and the other the Heavens, as vifible by Obfervation. The former is called the Terrestrial or Terraqueous Globe, the latter the Celestial.

Half a Globe or Sphere is called a Hemisphere.

The Terreftrial Globe is an artificial Representation of the natural Earth, having the whole Surface of the Land and Sea drawn upon it, in their natural Form, Order, and Situation.

The Spindle on which the Globe turns is called its Axis; which in the artificial Globe is real, in the natural only imaginary.

The two extreme Points of the Earth's Axis are its Poles, viz. the North, called the Arctic; and the South, called the Antarctic.

The Earth is fuppofed to be furrounded with several imaginary Circles, which are either drawn upon the artificial Globe, or expreffed by the Wooden and Brass Work about it.

Thefe Circles are diftinguished into Greater, and Leffer. The greater Circles divide the Globe into two equal Parts, the leffer into unequal.

Of the Greater Circles, viz. the Horizon, the Equator, Meridians, and the Ecliptic.

I. The HORIZON, which is expreffed by the upper Surface of the wooden Circle in which the Globe ftands, divides the Globe into an upper and lower Hemisphere.

This is called the Rational Horizon, to diftinguish it from the fenfible or apparent Horizon, which bounds our Profpect all round us, and which is greater or lefs, according as we ftand higher or lower. For Example, an Eye placed at five Feet above the Surface of the Earth or Sea, fees two Miles and a Quarter every way: but if it be at twenty Feet high, it can see five Miles and three Quarters.

The Rifing and Setting of the Sun and Stars properly refpects the Rational Horizon; that is, they rife when they get above it, and fet when they fink below it: But, by reafon of their vast Distance from us, the Rational and fenfible Horizon are to be confidered, in this Cafe, as one and the fame.

The wooden Horizon of the Globe has feveral Circles drawn upon it. The outermoft is marked with the Points of the Mariners Compafs; of which the East, West, North, and South, are called the Cardinal Points, dividing the Horizon into four Quarters. Each of thefe Quarters is fubdivided into eight Points, in all thirtytwo. These are alfo called Rumbs : ;; and Lines drawn from any Point upon the Surface of the Globe towards the feveral Rumbs, are called Rumb Lines. The other Circles upon the Horizon will be confidered afterwards. B 2 II, The

II. The EQUATOR divides the Globe into the Northern and Southern Hemifpheres. This is what Sailors call The Line; and when they pafs over it at Sea, they are faid to cross the Line. From this Line the Degrees of Latitude are counted towards the Poles, viz. go towards cach Pole *.

III. Semicircles reaching from Pole to Pole, and cutting the Equator at right Angles, are called MERIDIANS. 369 fuch Semicircles, drawn at equal Distances, quite round the Globe, mark the Degrees of Longitude, which are numbered upon the Equator, and are counted from the firft Meridian.

The Meridian which paffes through Fero, one of the Canary Hlands, is gene

*

Fig. 1.

rally

Every Circle, whether Great or Small, is fuppofed to be divided into 360 Degrees. Two Lines drawn from any two Points in the Circle to the Center (except two Points that lie in a ftrait Line with the Center, as A and E) from an Angle at the Center, which is called an Angle of fo many Degrees, as are contained in the Arch of the Circle betwixt the two Points. Thus an Angle of 90 Degrees, or right Angle, is meafured by of the Circle; an Angle of 45° by ACB is an Angle of 90°, BCD 45°, ACD 135°. N. B. A Degree is divided into 60 Minutes, a Minute into 60 Seconds, a Second into 60 Thirds, &c.

So much as any Angle, or Arch of a Circle, wants of 90 Degrees, is called the Compliment of that Angle or Arch; as DE is the Compliment of the Arch B D, and of the Angle B C D.