268 WENHAM LAKE IOE. [CHAP. XL. 



ice, and the other with English ice, the difference between the 

 quantity of cold stored up in each would be as appreciable as the 

 difference between a cellar full of gold and a cellar full of copper ; 

 that is to say, a cubic foot of Lower Canada ice is infinitely more 

 valuable, or, in other words, it contains infinitely more cold, than. 

 a cubic foot of Upper Canada ice, which again contains more 

 cold than a cubic foot of Wenham ice, which contains infinitely 

 more cold than a cubic foot of English ice ; and thus, although 

 each of these four cubic feet of ice has precisely the same shape, 

 they each, as summer approaches, diminish in value ; that is to 

 say, they each gradually lose a portion of their cold, until, long 

 before the Lower Canada ice has melted, the English ice has 

 been converted into lukewarm water.&quot; 



There can be no doubt that where an intense frost gives rise 

 to a great thickness of ice, permitting large cubic masses to be 

 obtained after the superficial and porous ice has been planed off, 

 a great advantage is afforded to the American ice merchant, and 

 the low temperature acquired by the mass must prevent it from 

 melting so readily when the hot season comes on, since it has first 

 to be warmed up to 32 Fahrenheit, before it can begin to melt. 

 Nevertheless, each fragment of ice, when removed from the store 

 house, very soon acquires the temperature of 32 Fahrenheit, 

 and yet when a lump of Wenham ice has been brought to En 

 gland, it does not melt by any means so readily as a similar lump 

 of common English ice. Mr. Faraday tells me that Wenham 

 Lake ice is exceedingly pure, being both free from air-bubbles and 

 from salts. The presence of the first makes it extremely difficult 

 to succeed in making a lens of English ice which will concentrate 

 the solar rays and readily fire gunpowder, whereas nothing is 

 easier than to perform this singular feat of igniting a combustible 

 body by the aid of a frozen mass, if Wenham ice be employed. 



The absence of salts conduces greatly to the permanence of 

 the ice, for where water is so frozen that the salts expelled are 

 still contained in air-cavities and cracks, or form thin films be 

 tween the layers of the ice, these entangled salts cause the ice to 

 melt at a lower temperature than 32, and the liquefied portions 

 give rise to streams and currents within the body of the ice, which 



