LIFE IN THE DEEP SEA. 579 



flagged, and I do not think lie ever missed the arrival of the 

 net at the surface. 



Often when the dredge or trawl appeared, there was nothing 

 in it at all, and then frequently a somewhat warm debate ensued 

 between the members of the scientific staff and the naval officers 

 as to whether the instrument had ever been on the bottom or no, 

 the scientific view being that it had not. 



Sometimes there would be only a bright red Shrimp in the 

 net ; and this fact, on the one side, would be held as proof that 

 the bottom had been reached, whilst, on the other, it was main- 

 tained that the Shrimp probably inhabited a region lying at some 

 distance above the bottom. The sledge irons of the trawl-net 

 were carefully examined as evidence in the matter, to test 

 whether they had been polished by friction on the bottom or 

 no, or whether they had any mud adhering to them. In future 

 dredging operations, it would be well to have a small cup with 

 a valve to it attached to the dredge or trawl, so that it shall 

 always retain a little of the bottom, and prevent the possibility 

 of the occurrence of such doubts. 



The conditions under which life exists in the deep sea, are very 

 remarkable. The pressure exerted by the water at great depths 

 is enormous, and almost beyond comprehension. It amounts 

 ' roughly to a ton weight on the square inch for every 1,000 

 fathoms of depth, so that at the depth of 2,500 fathoms, there is 

 a pressure of two tons and a-half per square inch of surface, which 

 may be contrasted with the 15 pounds per square inch pressure 

 to which we are accustomed at the level of the sea surface. 



An experiment made by Mr. Buchanan enabled us to realize 

 the vastness of the deep-sea pressure more fully than any other 

 facts. Mr. Buchanan hermetically sealed up at both ends, a 

 thick glass tube full of air, several inches in length. He 

 wrapped this sealed tube, in flannel, and placed it, so wrapped 

 up, in a wide copper tube, which was one of those used to 

 protect the deep-sea thermometers when sent down with the 

 sounding apparatus. 



This copper tube was closed by a lid fitting loosely, and with 

 holes in it, and the copper bottom of the tube similarly had 

 holes bored through it. The water thus had very free access to 



p p 2 



