INTRODUCTION. 77 



very little more pressure on things immersed in it 

 than air does, we must keep in mind, that as it 

 becomes deeper this pressure becomes, in a cor- 

 responding degree, increased, till, at the depth of 

 thirty-four feet the height of a column of water 

 is equal in weight to that of a corresponding 

 column of the whole atmosphere it presses upon 

 bodies immersed in it with the weight of two 

 atmospheres, and so on progressively for still 

 greater depths ; and it has accordingly been found 

 by experiment, that at very great depths, the 

 pressure is such as to drive in the most firmly 

 fixed corks of bottles, and to flatten the most 

 solid pewter vessels, which have been exposed 

 to it. 



Now, it is reasonable to believe, that fishes would 

 be materially injured by being subjected to any- 

 thing like such pressure as is competent to produce 

 these effects. Among the cetaceous tribes, the great 

 northern whale, on being harpooned by the fishermen, 

 sometimes descends, by strong muscular efforts 

 to such immense depths, that its body must have 

 been exposed to a pressure equal to that of many 

 atmospheres ; but it is not with impunity that it 

 does this. On the contrary, on rising again to the 

 surface, as it is sooner or later obliged to do to take 

 breath, it is found frequently to spout blood from 

 almost every outlet of the body, as the result of the 

 inordinate pressure to which it has been subjected, 

 or rather, perhaps, as the result of a return to the 

 ordinary pressure, after having been exposed to a 



