On the formation of Ice. 181 



coming so light as to remain on the surface, till it freezes at 

 32° ; of course, the upper layer freezes, while those below 

 are still above the freezing point, and are now cooled al- 

 most solely by the very slow conducting power of ice and 

 water — the currents of cold water down, and of u^armer 

 water up, by which almost exclusively the water was cool- 

 ed, before it arrived at 40°, being in a great measure pre- 

 vented, after the first film of ice is formed on the surface. 



Mankind are little aware how much they are indebted to 

 such apparently trivial laws for their comfort, and indeed 

 for their very existence ; for it is undeniable, that had the 

 creator omitted to endue water with this unparalleled pe- 

 culiarity of contraction, and had ice been as good a con- 

 ductor of heat as tiie metals, the polar seas would, even in 

 the early ages, have been frozen to the bottom ; all other 

 waters, not excepting the oceans within the tropics, would 

 have been successively converted into a solid as enduring 

 as granite; vegetable and animal life would have become 

 extinct ; — the very atmosphere might have congealed, and 

 in the language of Dr. Black, all nature would have be- 

 come a silent, lifeless, and dismal ruin. 



In the case of congelation which has elicited these remarks, 

 there was another circumstance worlhy of observation. 



The layers of ice were much more transparent in the di- 

 rection of their length than in the opposite ; this arose from 

 the distorted refraction of light occasioned by innumerable 

 air bubbles, from the size of duck shot to that of a small 

 pin's head, which were, in every instance, to be observed 

 at the junction of the layers, and at the top of each par- 

 ticular layer, excepting that on the surface, where there 

 were none. If we mistake not, these peculiarities can be 

 satisfactorily explained. It is well known that all natural 

 waters contain air in solution, and that it is expelled by boil- 

 ing, by the air pump, and by freezing. 



On the surface of the water, when the first layer of ice 

 was formed, there was nothing to retain the air bubbles ; as 

 they were evolved, they passed through the water and es- 

 caped. But after the first layer of ice was produced, the 

 air bubbles that were extricated by the chilling oi the wa~ 

 ter next below, were of course arrested by the ice, and 

 during the succeeding night were frozen in and detained. 

 Had the cold continued equally intense during ihe day as 



