The UNDERWATER CAMERA (fig. 17.3) has been extremely 

 useful for guiding the use of dredges and similar instrumentation 

 for recovering rocks. Rocks are not very readily available on 

 the bottom of the ocean. A lot of sediment pours down from the 

 rain of death in the ocean and covers everything pretty well, 

 so it is necessary to search pretty hard to find some rocks. You 

 do not just go around dredging at random. The underwater 

 camera is very useful for this purpose. In the bottom is an 

 electronic flash unit; near the top is the camera itself looking 

 out a porthole; at the very top is a transducer which sends out 

 a ping about every ten seconds as long as the camera is water- 

 borne, and squeals continuously when the camera hits bottom to 

 indicate that it is doing its job. 



There are many forms of the OCEAN BOTTOM TRAWL 

 of which figure 17.4 is one. These have to be rather rugged 

 instruments. Many times we have to break the rocks off for 

 they are not just lying around loose for the taking. They must 

 be broken off from the walls. This is hard duty for the wires, 

 winches, and trawls. The trawls have to be ruggedly made and 

 relatively inexpensive so we can afford to lose them fairly often. 



FIGURE I 7« 4 

 OCEAN BOTTOM 

 TRAWL 



181 



