GYROSCOPIC COMPASS METHODS OF SURVEYING 217 



borehole by the cable e. Compass and plumb are both 

 provided with a transmitter, which are connected by elec- 

 tric conductors in the interior of the holding cable to the 

 receiver aboveground. The two principal parts of the 

 plumbing cylinder are the gyrocompass and 

 the hanging plumb bob. 



The Gyrocompass. — Under the steel cover 

 there is a lead to the compass (Fig. 150). 

 The capped compass case a carries a three- 

 phase motor with a short-circuit rotor. 

 This consists of iron sheets with aluminum 

 rods and star plates. Over the axis a two- 

 pole alternating-current winding is slid. 



At an alternating current of 0.25 amp. and 

 120 volts, 500 periods, the body wheel of 

 the compass is made to rotate about its 

 horizontal axis at 30,000 r.p.m. The wheel 

 is closed about by a cap which hangs on a 

 floating ball bearing. The ball floats in a 

 vessel of mercury b (Fig. 150). On the float 

 body a small contact ball c is sprung. This 

 rotates with the wheel independent of the 

 mercury bath and the tube. Contact paths 

 d are fixed on the mercury bath and they 

 have slits. These turn independent of the 

 wheel with the bath and lamp e in the casing 

 jacket. The mercury bath has a Cardan sus- 

 pension, i.e., gimbals, in the lamp e and is connected to the 

 transmitter motor g by means of a spur wheel drive/ through 

 a shaft. This motor g rotates the bath and lamp as long as 

 the contact bead slides on one of the contact paths d. As 

 soon as the bead has reached the slit the electrical circuit is 

 interrupted and the turning ceases. Then the transmitter 

 motor has reached its previously known normal position 

 compared with the wheel. The motor of the transmitter is 

 connected electrically to the receiver motor, the graduated 

 scale of which turns back. Here one may read off the 

 position of the transmitter motor respecting the compass 



Fig. 150.— 

 Anschiltz appa- 

 ratus. The 

 gyrocompass. 



