THE GYROSTATIC COMPASS MARCHAND. 



113 



trie motor, and entirely free to turn in any direction were it not for 

 two small springs, which serve to represent the attraction due to 

 gravity and tend to keep the gyroscope's axis tangent to the surface 

 of the sphere upon which it is mounted. This apparatus may be 

 slipped along a large movable metallic circle representing a meridian. 



When the springs are detached, the axis of the gyroscope tends to 

 take an invariable direction and to depart from it only because of the 

 inevitable friction which is present at the pivots. 



However, once these springs are attached, if the meridian circle 

 is moved to another place on the globe, then the axis will change so as 

 to come into the plane of the circle, one of its extremities being directed 

 toward the upper pole of the circle. According to the direction of 

 the gyroscope and that 



of the circle, one or the g-p C 



other end of the axis 

 moves so as to point to 

 this upper pole. 



In the Anschutz 

 compass, of which fig- 

 ure 1 is a sectional and 

 plate 2 a perspective 

 view, the gyrostat is 

 similarly driven by a 

 three-phase electric 

 motor; the float from 

 which the gyroscope is 

 suspended is a hollow 

 bowl of steel partially 

 immersed in a mer- 

 cury bath contained in 

 an annular box, also of 

 steel. To the top of 

 this float is fixed the 

 compass card. The north-south line of the card coincides exactly 

 with the direction of the axis of the gyrostat. 



The small motor which rotates the gyrostat disk is so constructed 

 that its stationary part is built on the box of the gyrostat. The 

 electrical connections to the exterior are made for two of the circuits 

 through small cups of mercury. The third circuit passes through the 

 mercury bath containing the float and then through the case itself. 

 The rotor is rigidly built on the gyrostat disk. It is of one piece, 

 spindle and all, and made of nickel steel. It is provided with ball 

 bearings of extra-hard steel and makes 20,000 revolutions per min- 

 ute. The axle is of the Laval type or "flexible axle." Its great 

 38734°— sm 1911 8 



Fig. 1. — Anschutz gyrostatic compass. Vertical section. A, three- 

 phase alternating-current motor in box B (the rotor of the motor 

 serves as the gyrostat); R, compass card; S, hollow annular steel 

 float, floating in the mercury Q and counterbalancing the weight 

 of the moving system; K, compass box, suspended as usual by 

 gymbals; S, T, special suspension, made of two insulated conduct- 

 ors for leading in two branches of the three-phase current, the third 

 circuit being made through the floating ring and the surrounding 

 mercury. 



