CHAP. XL.] WENHAM LAKE ICE. 361 



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 con 

 verted into luke-warm 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 frag 

 ment of ice, when removed from the store-house, 

 very soon acquires the temperature of 32 Fahren 

 heit, and yet when a lump of Wenham ice has been 

 brought to England, 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 ex 

 ceedingly pure, being both free from air-bubbles and 

 from salts. The presence of the first makes it ex 

 tremely difficult to succeed in making a lens of En 

 glish ice which will concentrate the solar rays and 

 readily fire gunpowder, whereas nothing is easier 

 than to perform this singular feat of igniting a com 

 bustible body by the aid of a frozen mass, if Wenham 

 ice be employed. 



The absence of salts conduces greatly to the per 

 manence of the ice, for where water is so frozen that 



VOL. II. K 



