the ends of the magnet. This is where the highest

concentration of magnetic lines of force exist.

However, the earth's magnetic poles are not at

the geographic poles, nor are they antipodal

(opposite) to each other.

The intersection of a sphere and a plane is a

circle. The intersection is a great circle if the plane

passes through the center of the sphere. It will be

a small circle if it does not.

Look at figure 7-2. Here, the earth's equator

is a great circle. If a second plane (fig. 7-3) passes

through the earth parallel to the equator, its

intersection is a small circle. Small circles don't

always have planes perpendicular to the polar axis.

However, if they are perpendicular, then all points

on the small circle are equidistant from the

equator; that is, the circles are parallel to

the equator. Such small circles, together with

the equator, are PARALLELS. They provide

one component of a system of geographical

Now, suppose that planes pass through the

same as an address *at the corner of Fourteenth*

earth's poles (fig. 7-4). Such planes contain the

axis, and since they also contain the center, they

different names for identifying the parallels and

form great circles at the surface. Great circles

meridians.

through the poles of the earth are MERIDIANS.

The circumference of a circle is divided into

All meridians are perpendicular to the equator.

360 units. This unit is the *degree. *It is the same

Meridians form the second part of a system of

unit you use to measure an angle. In figure 7-5,

geographical coordinates commonly used by

navigators.

You can identify any point on earth by the

intersection of a parallel and a meridian. It is the

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