DEEP-SEA nous DING. 7 



with liooks, especially for the Caspian. Others, 

 guided by theory, have devised petards which were 

 to be exploded, or bells which were to be rung, a 

 certain number of feit below the surface of the 

 ocean ; and it was hoped that an echo would be heard 



Vig. 4. — Measuring tlie Depth of the Sea by means of a Bomb. 



from the bottom, the distance of which could of 

 course be calculated. Experiments of this kind were 

 made when the winds were hushed and all was still ; 

 but echo was silent. M. de Tessan suggested the 

 more likely method of letting a bomb fall into the 



