196 DEEP BOREHOLE SURVEYS AND PROBLEMS 



keeps it horizontal, and the upper half 15 is a hollow dome. 

 In an annular recess inside the bowl 33 is a strip of sensitized 

 paper fixed relative to the bowl in which the needles move. 

 The needle pivot in the bottom part of the bowl 33 holds 

 the needle, which is a standard sewing needle, on carrier 

 62. There are four of these rectangular needles; two 30 

 flat, and two 31 on edge on the bearing spider 29. This 

 spider has two opposite holes at right angles to the center 

 lines of the needles, and two white paper reflectors 65 

 opposite the holes. In the cradle on the compass side of 

 each lantern is a diaphragm 34 (Fig. 2) with a bell-mouthed 

 hole with clip held screens. A number of screens of tracing 

 cloth are placed in these to adjust the intensity of light 

 on the dome. The compass has a sliding cover 13 over 

 the upper half and is finished dead white inside for even 

 lighting. This all provides uniformly diffused light of 

 suitable intensity within narrow limits. 



The controller is for determining the length and interval 

 of exposures which may be two or four per hour, dependent 

 on the setting of contact finger 44. A control screw 50 

 (Fig. 1) insulated from the control base 49 is prolonged into 

 a spring plunger 38 by means of which a good contact is 

 made to the dry battery. Owing to the high-pitch, left- 

 hand thread on this small diameter screw the drum retreats 

 from the clock when it is revolved by the crank. This 

 crank is fixed to the minute-hand spindle of the clock and 

 drives the drum through the insulated pin 50 projecting 

 from the spider 52 carrying drum 51. This drum has four 

 longitudinal metal contact strips 45 in electrical connection 

 with the spider for giving two or four exposures per hour. 

 The circumferential width of these strips is such that a 

 series of exposures of increasing length are got during each 

 revolution of the drum, and this enables the records to be 

 identified. The drum contacts, as shown by the finger 44, 

 on slide 41. 



At the end of carrier tube 39 is the clock 48 with its minute- 

 hand spindle extended to carry a crank 47 with a milled 

 setting knob 54 on opposite ends. It is readable from the 



