14 THE BOTTOM OF THE SEA. 



adding its pressure to that of the superincumbent 

 air, and water being estimated at 1300 times the 

 weight of air, it is plain that calculations which have 

 been made relative to the atmosphere would, a 

 fortiori, seem to be possible also relative to the ocean. 

 An instrument so constructed as to indicate the 

 pressure to which it had been subjected in the water 

 would serve to complete or correct the results given 

 by the sounding apparatus. Discordant indications 

 would possibly afibrd evidence as to the direction and 

 force of submarine currents. 



If we add to the imperfection of the processes 

 themselves the difficulties of an accidental character 

 which attend their application, we shall find but 

 little reason for wonder that submarine orography is 

 so little advanced. To make deep-sea soundings, a 

 ship must be provided with a considerable amount of 

 materiel of no use for any other purpose. A single 

 operation during a voyage must employ several per- 

 sons, and it could only be made in fair weather. In 

 general, therefore, merchant-ships cannot be provided 

 with instruments and with hands to make deep-sea 

 soundings; they would require cables or lines some 

 four miles in length, and their crews would seldom be 

 strong enough to deal with such heavy tackle. '^Phen, 

 the time spent in such operations would occasion incal- 

 culable loss to merchants and ov/ners ; and if the 



