558 



Subsurface Geologic Methods 



of the angle unit upon a metal-edged disc of bromide photographic paper. 

 The angle unit consists of a skeleton-type plumb bob suspended in a uni- 

 versal mounting with a ring carrying two cross hairs forming its base. 

 Immediately below is a glass, on which are etched concentric rings rep- 

 resenting degrees of drift. This glass also serves as the top closure of the 

 fluid-filled compass chamber. Within this chamber a compass card marked 

 in bearings is free to turn on a spring-mounted pivot needle. The compass 

 mechanism is lubricated and buffered from extreme shock by compass 

 fluid. A sylphon, which closes the bottom of the compass cup, permits 

 expansion of the fluid when the instrument is used in high-temperature 

 wells. 



A loader and an unloader (fig. 279) make possible the insertion 



Figure 279. Loading disc in single-shot instrument (top), 

 single-shot instrument (bottom). 



Unloading disc from 



and removal of the sensitized disc from the machine in daylight. The 

 loader fits snugly over and engages a slot in the machine. By pressing 

 a knob in the instrument the slug trap is opened. The loader slide is 

 raised and lowered to force a disc into the machine, after which the trap 

 is closed by releasing the knob. Developing of the disc is accomplished 

 by filling the base of the unloader with developer-fixer solution. The in- 

 strument is placed on the unloader so that the slots coincide, and the un- 

 loader handle is turned to a horizontal position. When the slug trap is 

 opened by pressure on the knob in the instrument, the disc falls into the 

 unloader and is immersed in the solution. After the handle on the un- 

 loader is closed, the single-shot machine is removed. Four minutes is 

 suflBcient time for developing and fixing the disc, after which it may be 

 washed in clean water and read. An illustration of a reading from the 10- 



