160 FOUNDERS OF OCEANOGRAPHY 



Water is almost incompressible — under one additional 

 atmosphere it is compressed to the extent of only one-twenty- 

 thousandth of its bulk, and this very sUght compressibihty 

 decreases with increase of pressure. At 4,000 metres (2,187 

 fathoms) water becomes only 1-75 per cent, heavier, and a 

 solid mass of iron of 1,000 grams shows at 4,000 metres only 

 the insignificant difference of 0-3 per cent, in weight. Sub- 

 stances are thus seen to be practically as heavy in deep 

 water as in shallow, and will sink as rapidly. A brass 

 weight " messenger " sent down a line to close some apparatus 

 takes just four times as long to reach its objective at 2,000 

 metres as it does to arrive at 500 metres. Any object that 

 sinks in a foot of water will go to the bottom whatever the 

 depth is ; and the floor of the ocean at great depths is 

 covered with delicate shells, which are very light and yet 

 have sunk from the surface to the bottom. Solid objects, 

 or those that are freely permeable to the water, so that the 

 pressure can be equalised throughout, such as the body of 

 an animal, remain practically unchanged ; but substances 

 with internal cavities containing air are strongly compressed 

 and distorted under the enormous pressure of tons on the 

 square inch at great depths, and may collapse into fragments. 

 For example, the beam of the " Challenger " trawl came up 

 from its first deep-sea trip with the wood so much com- 

 pressed that the denser knots stood out from the surface, 

 and Mr. Buchanan tells how a hollow brass cylinder with 

 closed ends had been squeezed flat, and thermometers and 

 closed glass tubes, wrapped up in cloth and protected by a 

 copper case, came up crushed to powder, from a depth of 

 3,000 fathoms. Sir Wyville Thomson called this collapse 

 under pressure an " implosion." 



These facts completely dispose of the popular delusion 

 that, on account of the great and increasing pressure, water 

 in the sea becomes denser and denser with increase of depth, 

 and that all objects which sink at the surface — ships and men, 

 iron, lead, and gold—" find their level " and there remain 



