tact stud attached to the compass frame and a fork attached to a collar that can turn with a certain amount of friction about the phantom shaft. When the ship starts to turn in either direction, the friction between the cut-out switch and the phantom shaft carries the switch around and brings one prong or the other into contact with the fixed contact stud. This completes the electric circuit through the solenoid and causes the cut-out valve to close. If the ship had turned in the opposite direction, the other prong would have made contact and the valve would be closed as before. The distance between the prongs is such that contact is always made before the ship has turned more than about 10 degrees. After the ship has ceased turning, the yawing of the ship back and forth quickly breaks the switch contact, and normal damping is resumed.
147. Avoidance of the Quadrantal or Rolling Error. - A compass with a single gyro is subject to an error when on a rolling ship on an intercardinal course (Arts. 115, 116). This error is avoided in the Arma, as in the AnschUtz gyro-compass, by the use of two gyros with the spin-axles inclined to one another (Art. 140).
§7. The Florentia Gyro-Compass
148. Arrangement of the Principal Parts of the Florentia Master Compass. - The sensitive element of this instrument,* made by the Officine Galileo, Florence, Italy, consists of a single meridian-seeking gyro-wheel in a case, G, Fig. 197, hanging from a hollow ring F that floats in an annular trough of mercury T. The gyro has a mass of about 5 kg. and a moment of inertia of about 70,000 gm. em'. It rotates at a speed of 20,000 revolutions per minute.
The mercury trough T hangs from a vertical spindle carried by a ball-bearing on the horizontal frame or spider D. The spider is suspended by gimbal rings, R,R2, from the top of the binnacle B. The lubber line is engraved on an arm L fastened to the spider. The compass card C is fastened on top of the spindle. The rigidly connected system from the mercury trough to the compass card constitutes the phantom element, P. The phantom element is stabilized by a second gyro SG within a casing directly below the compass card. By means of a reversible motor M, pinioned to a
' U. S. Patent. Martienssen, No. 1493213, 1924.