Captain Parri/s intended Expedition to the North Pole. 91 



is accomplished, I apprehend, in the following way. It is a well 

 known fact, that fresh water, at the temperature of 39J°5 is 

 specifically heaviest ; and that it possesses the strange peculiarity 

 of becoming hghter by the farther reduction of temperature ; 

 and at that point where it passes into ice, its expansibihty, if 

 we except its vaporous state, is at its maximum. The same law, 

 a little modified, regulates the freezing of salt water ; the points 

 of greatest density and consolidation being probably a little 

 lower than in fresh water. 



When water is completely frozen, it, like other bodies, con- 

 tracts by a continued abstraction of caloric. Now, if a body of 

 ice, twenty or thirty feet thick, floats in water at the freezing 

 point, the under surface of that ice will be nearly of the same 

 temperature as the water, and the upper surface may correspond 

 with the temperature of the superjacent atmosphere, which, 

 during winter, in high latitudes, depresses the thermometer to 

 40° or 50° below zero. Such a difference of temperature must 

 produce a very great difference in specific gravity, and the up- 

 per surface must be much more contracted than the under ; but 

 as the cold increased progressively, it might happen that no evi- 

 dent effect would be produced by this great difference, as the 

 accumulating mass accommodated itself to the gradual change : 

 but as soon as the summer returns, the temperature of the air 

 is speedily raised, communicating its caloric to the surface of the 

 ice, which begins to expand, and ultimately exerts energy suffi- 

 cient to overcome the cohesive force of the frozen particles, and 

 a rent is the consequence ; which, as soon as it has commenced, 

 runs unrestrained in all directions ; and the advancing summer, 

 modifying the winter's sway, prevents reunion, till the attach- 

 ment is set loose by the currents, or drifted off by the winds. 



The effects originating in the influence of the vicissitudes of 

 temperature in tearing asunder the ice, are awfuUy illustrated 

 by the aspect of the polar glaciers, which are found in the val- 

 leys on shore *. The ice being upwards of 200 feet thick, the 

 hideous chasm yawns horribly to the very bottom, from the 

 brink of which the beholder turns away with indescribable feel- 

 ings of horror. 



• See Icebergs, Phil. Journ. 1819. 



