GYROSCOPIC COMPASS METHODS OF SURVEYING 223 



The camera^ (Fig. 3) which is of special design employs 

 a 16-nim. perforated motion-picture film and has a capacity 

 of 50 ft. There are two lenses recording pictures simultane- 

 ously in opposite directions, up and down. One lens 

 photographs the compass scale and gyroscopic pointer 

 below with the watch and thermometer (if any), while 

 the other photographs the position of the bubble in the 

 graduated level gage box above. These lenses have to be 

 very accurately aligned on the same optical axis and focus, 

 thus superimposing two pictures on one film as shown in 

 Fig. 6, Plate XIV. This enables one to read off the amount 

 and direction of deflection at the same time, while the time 

 for the depth computation is given as well. The film 

 take-up is worked through gears by a small electric motor, 

 which also operates a synchronized and adjustable contact 

 device providing the necessary light flashes for taking the 

 pictures. The camera motor is controlled by an accurate 

 timing device guaranteed to vary less than 7 sec. per day. 

 Thus the camera has a capacity for taking up to 1,000 

 photographs, giving a practically continuous record of the 

 hole. It also records going into, and coming out of, the 

 hole. 



The hox level gage (Fig. 2) is a ring with top and bottom 

 of ground special glass, the former disc being spherical and 

 having concentric graduations. The position of the bubble 

 relative to these graduations gives the amount of vertical 

 inclination as in the depthometer of a previous chapter. 

 Three different levels are provided with each instrument 

 having maximum inclinations of 20, 40 and 55 deg., 

 respectively. This range of registration of dip angle far 

 transcends that of any other device employing the gyro- 

 static principle. Preliminary runs with an acid-bottle 

 apparatus decide which of these box level gages to select 

 for a particular case. To ensure rapid response of the 

 bubble to quickly altering inclinations the nature and 

 size of the bubble are specially allowed for in the material 



1 We are indebted here for some notes kindly supplied by the makers, 

 The Sperry-Sun Well Surveying Company, Philadelphia, 



