248 NAVIGATIONAL COMPASSES
horizontal gear on the phantom element P, the latter is kept in fixed position relative to the meridian-seeking axle of G.
The sensitive element S is kept central with respect to the annular trough by two pins p', p. The upper pin is attached to the phantom and projects into a small ring fastened to the sensitive element. The lower pin is attached to the gyro-casing G and projects into a slot q in the end of an arm fastened to the phantom element. The center of mass of the sensitive element is about
THE FLORENTIA GYRO-COMPASS 249
plane of the spin-axle of the meridian-seeking gyro, the balls are midway between the two vertical plates. When the phantom turns relative to the spin-axle of the meridian-seeking gyro, one of the balls comes into contact with one of the vertical plates, thereby completing an electric circuit through the follow-up motor
0.8 cm. below the center of buoyancy. The Florentia gyro-compass is slightly pendulous.
The gyro of the sensitive element is the rotor of a three-phase motor. One of the three phases is led to the motor through the supporting spindle. The other two are led through two flexible platinum strips that extend from the phantom to the gyro-casing.
149. The Follow-Up System. - The upper end of a vertical helical spring is suspended from the upper plate of the sensitive element. On the lower end of the spring is a pair of silver balls, Fig. 198. These balls hang between a pair of vertical metal plates X, X', Fig. 199, mounted on a frame carried by the phantom element.
When the north-south line of the compass card is in the vertical
M mounted on the spider. The motor rotates the phantom till neither ball touches a contact plate, that is, till the north-south line of the compass card is in the vertical plane through the spinaxle of the meridian-seeking gyro. Really, the motor rotates the phantom slightly beyond the equilibrium position, so that the other vertical plate is brought into contact with the hanging balls and the direction of rotation of the motor is reversed. Thus, the compass card is caused to " hunt " back and forth through an
