Figure 4-9.--Apparent rotation of a gyroscope at 45N latitude.

line passing through the center of the gyroscope and

parallel to the earth's axis. This apparent rotation is in a

counterclockwise direction when viewed from south to

north. The path that the north axle describes in space is

indicated by the line EAWB back to E (fig. 4-10).

The effect of the earth's rotation causes the north

end of the gyroscope axle to rise when east of the

meridian and to fall when west of the meridian in any

latitude. This tilling effect provides the means by which

the gyroscope can be made into a north-seeking

instrument.

MAKING THE GYROSCOPE INTO A

GYROCOMPASS

Up to this point, we have discussed the basic

properties of a free gyroscope. Now, we will discuss

how we use these properties, rigidity of plane and

precession, to make a gyroscope into a gyrocompass.

Figure 4-9.--Apparent rotation of a gyroscope at 45N

latitude.

The first step in changing the gyroscope to a

gyrocompass is to make a change in the suspension

system. The inner gimbal that holds the gyro rotor is

modified by replacing it within a sphere or case (fig.

(aligned north-south) and parallel to the earth's surface

4-11, view A), a necessary feature that protects the rotor.

at 45 north latitude and 0 longitude (fig. 4-9).

A vacuum is formed inside the sphere to reduce air

A gyroscope, if set on any part of the earth's surface

friction on the spinning rotor. The next step is to replace

with the spinning axle not parallel to the earth's polar

the simple gyroscopic hose with what is called a

phantom ring (fig. 4-11, view A). The difference

axis, appears to rotate, over a 24-hour period, about a

Figure 4-10.--Path of the spinning axis of a free gyroscope.

4-6