Chap, xxii.] PRESSURE AT GREAT DEPTHS. 503 



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

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

 to the interior of the tube when it was lowered into the sea, 

 and the tube was necessarily constructed with that object in 

 view, in order that in its ordinary use the water should freely 

 reach the contained thermometer. 



The copper case containing the sealed glass tube was sent 

 down to a depth of 2,000 fathoms, and drawn up again. It was 

 then found that the copper wall of the case was bulged and 

 bent inwards opposite the place where the glass tube lay, just 

 as if it had been crumpled inwards by being violently squeezed. 

 The glass tube itself, within its flannel wrapper, was found when 

 withdrawn, reduced to a fine powder, like snow almost. 



AVhat had happened was that the sealed glass tube, when 

 sinking to gradually increasing depths, had held out long against 

 the pressure, but this at last had become too great for the glass 

 to sustain, and the tube had suddenly given way and been 

 crushed in the violence of the action to a fine powder. So 

 violent and rapid had been the collapse that the water had 

 not had time to rush in by means of the holes at both ends 

 of the copper cylinder, and thus fill the empty space left behind 

 by the collapse of the glass tube, but had instead crushed in 

 the copper wall, and brought about equilibrium in that 

 manner. 



The process is exactly the converse of an explosion, and is 

 termed by Sir Wyville Thomson an "implosion." Gunpowder 

 exploded in the centre of a similar copper tube would in a 

 corresponding manner have bulged the sides of the tube out- 

 wards, notwithstanding the existence of the openings nt its 

 ends. 



Marine animals, no doubt, easily accommodate themselves to 

 these enormous pressures in the deep sea. Their tissues being 

 entirely permeated by fluids, the pressure has little or no 

 effect upon them. Moreover, amongst all the various animals \ 

 dredged up from great depths, it is only some fish which > 

 show any marked effects of the alteration of pressure to which 

 they are subjected in being brought to the surface. Fish with j 

 swimming bladders come up in the deep-sea dredge in a horribly t 

 distorted condition, with their eyes forced out of their heads, [^ 

 their body tense and expanded, and often all their scales 

 forced off. . > 



No sunlight penetrates the deep sea ; probably all is dark 

 below 200 fathoms, at least excepting in so far as light is given ( 

 out by phosphorescent animals. At depths of 2,000 fathoms ' 

 and upwards the temperature of the water is never many 

 degrees above the freezing-point. 



