48 A Retrospect of Oceanography 



and progressive retardation. The line was always allowed 

 to run out free from coils on the deck and without any break 

 or resistance. 



Perhaps the greatest advantage which hemp line has over 

 \vire for sounding, and more particularly for dredging in deep 

 water, is that it loses about 70 per cent, of its weight when 

 immersed in water, whereas the wire loses only 13^ per cent. 

 Thus, the No. i line weighs in air 200 Ibs. per thousand fathoms 

 and only 60 Ibs. in water. The same length of sounding- 

 wire weighs 14^ Ibs. in air and 12-6 Ibs. in water. The breaking 

 -train of the line is 14 cwt. or 1568 Ibs., that of the wire is 

 210 Ibs. The length of the line which weighs 1568 Ibs. in water 

 is 26,000 fathoms, while that of the wire which weighs 210 Ibs. 

 in water is 16,700 fathoms. Therefore, granting that we 

 can sound in 16,700 fathoms with wire, there are nearly 10,000 

 fathoms more that can be explored only with hemp, and 

 beyond 26,000 fathoms, if such depths existed, we should 

 not be able to explore them at all. 



Of course these limiting depths are purely theoretical, 

 because, each being at its breaking strain, neither the line 

 nor the wire could be hove up from them. They serve, however, 

 to accentuate a very real advantage which the hemp line has 

 over the metal wire. This advantage will make itself practically 

 felt in dredging in the great depths of 4000 and even 5000 

 fathoms which are now known to exist. For instance, the wire 

 rope used by Agassiz on board the " Blake " had a circumference 

 of ij inch. One fathom of it weighed 1-14 Ibs. in air and I Ib. 

 in water. Its breaking strain was 8750 Ibs., so that its breaking 

 length was 8750 fathoms in water and at rest. It is obvious 

 that if it were to be used for dredging in 5000 fathoms the 

 remaining 3750 Ibs. would be quite inadequate to bear the 

 weight of the dredge with its contents, and the strain which 

 would have to be exerted in order to bring it up in a reasonable 

 time, to say nothing of the margin for safety, or of the resistance 

 while being dragged over the ground. 



Much misunderstanding prevails about the relative rapidity 

 with which sounding and dredging operations can be carried 

 on with hemp and with wire. In well-appointed cable ships, 



