24 ' DEPTHS OF THE OCEAN 



of 3000 fathoms of line in water was roughly 108 kilos. When 

 heaving the lead the weight used was sometimes 150 and 

 sometimes 200 kilos. During the whole of the voyage of the 

 "Challenger" only two temperature lines with eight ther- 

 mometers, and nine sounding-lines with thirteen thermometers, 

 were lost ; eleven thermometers collapsed under high pressure 

 at great depths. 



For dredging and trawling they employed hemp lines 2, 2^, 

 and 3 inches in circumference, with a breaking strain from 1600 

 to 2550 kilos, spliced together to form a length of 4000 fathoms, 

 which was coiled on the forecastle (1,2, and 3). An attempt 

 was made to use swivels to keep the line from twisting, but 

 this had to be abandoned owing to their being damaged in the 

 blocks. 



It is evident that in the arrangement and working of all the 

 apparatus account had to be taken of these immense lengths of 

 line. In the first place, they were extremely bulky, and required 

 a large amount of deck space for coiling and handling, as the 

 line had first to be led from the forecastle to the winch, and 

 frequently from the end-drum on one side of the axle to its 

 fellow on the other side, when the strain on the dredging rope 

 was so great that the friction of the revolving drum was not 

 sufficient to make it bite. This happened sometimes even when 

 ten or twelve men were holding on abaft the winch. A second 

 important consideration was the severe strain on the line every 

 time the big heavy ship lurched, or when the lead or the dredge 

 stuck fast on the bottom. 



The weight of 3000 fathoms of sounding-line in water was, 

 as already stated, over 100 kilos, and the weights amounted to 

 200 kilos, so that there was not much margin left for friction in 

 the water and accidental jerks, when we remember that the 

 breaking strain was only 700 kilos. Accordingly, when sound- 

 ing or trawling great care had to be taken to provide against 

 such contingencies, and large accumulators were used, consisting 

 of rubber bands 3 feet long and J-inch thick, which could be 

 extended to 17 feet, and thus counteracted sudden jerks on the 

 line. For sounding, forty of these were employed, while for 

 trawling there were as many as eighty, which together could 

 support 2J tons, or the breaking strain of the line. 



Fig. 2 shows the two accumulators, one for sounding 

 and the other for trawling, attached to blocks high up on a 

 yard, thus enabling them to expand and contract freely. 



Before sounding all sail was taken in, and the ship was 



