PHOTOGRAPHIC METHODS 181 



place near the borehole. A transformer within the instru- 

 ment is provided for reducing the tension of the electric 

 current. Current at, say, 220 volts, is used to transmit 

 electricity in the long cable with little loss, and it is reduced 

 to lower tension for easier manipulation in the instrument. 

 An automatic switch is introduced to make the connections, 

 such as switching on the motor or the lights. 



The clean water is injected through the tube h, and the 

 mud-laden water is forced out through the aperture i. 

 This arrangement enables the apparatus to be employed 

 in mud-laden boreholes by replacing the dirty water with 

 clear water. In the case of oil wells, where an oily film 

 on the object glass would interfere with the photograph, 

 it has been proposed to wash with benzine instead of water. 

 By changing the rubber packing rings x and y the same 

 instrument may be employed in boreholes varying from 

 5>^ to 12 in. in diameter. 



Near the lower end of the instrument a compass needle e 

 covered with a graduated disc is placed. A small lamp I 

 throws light on this disc, so that part of it is photographed 

 at the same time as the principal photograph is taken, the 

 rays passing by the side of the mirror d. In this way 

 the direction of every face of the rock is recorded on the 

 photographs. 



In operating the apparatus it is lowered from the drill 

 pipe to the depth at which information is required. Clear 

 water is then turned on, and in about 10 min. the original 

 slimy water is replaced, the view being then clear enough 

 to start photographing. This is done by switching on the 

 light for 10 or 15 sec. The film is changed by drawing it 

 through the camera by means of the motor, and another 

 photograph may then be taken. The instrument may be 

 turned round so as to cover the whole of the circumference 

 of the borehole with six or eight exposures, according 

 to the diameter of the hole ; in a 6-in. hole six exposures are 

 sufficient, but in larger holes eight or more exposures are 

 required. The instrument may be raised or lowered to 

 photograph fresh sections. A good idea of the walls of a 



