On the Depth and Saltness of the Ocean. 29 



lost, — consequently, the experiments are expensive as well 

 as inconvenient to make ; the time required for the experi- 

 ments taken in this way, is half an hour for the descent of the 

 weight ; the line in these cases, instead of being used from 

 the ship, is lowered from a boat to avoid the drift of the ves- 

 sel, which is very considerable during the time the weight is 

 descending ; this renders the experiment more satisfactory 

 and correct. It will thus be seen, that it is out of the power 

 of an ordinary vessel to make the experiments. In order that 

 this interesting inquiry may advance without these difficulties, 

 it becomes necessary that some new mode of sounding be 

 adopted, whei'eby both the time may be lessened and the op- 

 portunities multiplied. It has been suggested to obtain an 

 echo from the bed of the ocean by the explosion of a shell 

 just beneath the surface, the depth to be measured thi'ough 

 the propagation of reflected sound. The mode which appears 

 to me more effective, is by the time of descent and direct 

 waves of sound from an explosion at the bottom, which might 

 be accomplished by charging the shell with some of the ex- 

 plosive compounds ; the momentum acquired by the descent 

 of the shell would cause explosion on striking the bottom ; 

 the great difficulty which seems to present itself, is the pre- 

 servation of the charge of the shell from damage by the enor- 

 mous pressure to which it would be subjected in its descent. 

 Such experiments would naturally lead to interesting inves- 

 tigations relative to the descent and movement of bodies 

 tlirough water, and I'esult in establishing the laws to which 

 they are subject ; an inquiry that has been but partially car- 

 ried out. 



Although the experiments to ascertain the depth of the 

 ocean have been few, and without any regular order, yet they 

 afford evidence, and jirepare us for some interesting results in 

 future. Among them is one, that the great depressions or sub- 

 marine valleys run nearly at right angles to the gi'eat mountain 

 chains of this continent: for instance, we are led to believethat, 

 at the equator, there is a depression to neai'ly the 5tli parallel 

 of south latitude, where a ridge occurs ; at the I5th parallel, 

 we find another depression ; 10^ farther south, we have an- 

 other ridge ; it again deepens and rises twice towards tlio 



