THE PHYSICAL CONDITIONS OF THE ABYSS 19 



movement of tlie water, the bottom is composed of a 

 uniform fine soft mud, and there is no plant life. 



All of these physical conditions we can appreciate 

 except the enormous pressure. Absolute darkness 

 we know, the temperature of the deep seas is not an 

 extraordinary one, the absence of movement in the 

 water and the fine soft mud are conditions that we 

 can readily appreciate ; but the pressure is far greater 

 than anything we can realise. 



At a depth of 2,500 fathoms the pressure is, 

 roughly speaking, two and a half tons per square 

 inch — that is to say, several times greater than the 

 pressure exerted by the steam upon the piston of 

 our most powerful engines. Or, to put the matter in 

 other words, the pressure per square inch upon the 

 body of every animal that lives at the bottom of the 

 Atlantic Ocean is about twenty-five times greater 

 than the pressure that will drive a railway train. 



A most beautiful experiment to illustrate the 

 enormous force of this pressure was made during the 

 voyage of H.M.S. ' Challenger.' I give the description 

 of it in the words of the late Professor Moseley. 



' 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 



