98 THE OCEAN 



This is true at least for all substances more 

 compressible than water. We have proof of 

 this in the fact that the whole floor of the 

 ocean is strewn with the delicate calcareous 

 and siliceous shells of organisms which once 

 lived in the surface waters. 



In March, 1873, during the " Challenger " 

 Expedition, the two thermometers sent to the 

 bottom in 3875 fathoms collapsed owing to 

 the great pressure. J. Y. Buchanan then took 

 three glass tubes of different calibres, sealed at 

 both ends, wrapped them in a cloth, and 

 enclosed them in a cylindrical copper case 

 having the ends pierced with holes in order 

 to permit the free passage of water. The case 

 was sent down to 2800 fathoms, and when it 

 came up again it looked as if it had been 

 struck in the middle with a hammer. On 

 being opened the cloth was found to be full 

 of what looked like snow but was in reality 

 finely comminuted glass ; the two wider glass 

 tubes had collapsed, while the narrow one 

 was still intact. 



The experiment was repeated later, only 

 one glass tube being used and sent down to a 

 depth of 3000 fathoms. The copper case 

 was again indented at that portion occupied 

 inside by the sealed glass tube, which was 

 reduced to powder. It seems that the sealed 

 glass tube, while sinking, had held out long 



