. Deep borehole surveys and problems. Boring. Fig. 116.—Atwood's borehole camera with parts removed to their relative places outside the case. burning, the wall is brightly illuminated. In making an exposure with a No. 16 stop the lights are turned on for about 20 sec. Before making a second exposure the camera is lowered or raised 43-^ in., the distance covered by one photograph, and a new part of the film is turned into place by making and breaking the circuit of an electromagnet acting upon the roll of film. In this way a series of 50 or more photographs can be taken at the rate of 1 a minu
. Deep borehole surveys and problems. Boring. Fig. 116.—Atwood's borehole camera with parts removed to their relative places outside the case. burning, the wall is brightly illuminated. In making an exposure with a No. 16 stop the lights are turned on for about 20 sec. Before making a second exposure the camera is lowered or raised 43-^ in., the distance covered by one photograph, and a new part of the film is turned into place by making and breaking the circuit of an electromagnet acting upon the roll of film. In this way a series of 50 or more photographs can be taken at the rate of 1 a minute, and they will show a continuous strip of the wall for a distance of 20 ft. or more. The win- dow, which is 13^^ by 5K in. is set in litharge cement. A guard strip is riv- eted to the tube on each side of the window. The hoisting cable is attached to the hook g, 4 in. behind the window, so that in the ordinary 6-in. drill hole the window always hangs near the wall. The mirror, lamps and reflectors are mounted ^^g- ii7.—Camera . , T , 1 y^^th. side removed. on an oak plate, which can be adjusted to bring the mirror in the right position behind the window (Fig. 117). The two lamps are 10 volts and 5 cp. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Haddock, M. H. (Marshall Henry). New York, McGraw-Hill
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