246 HEAT. 



never tires, and wants no sleep. It is not subject to 

 any malady when originally well made, and only re- 

 fuses to work when worn-out with age. It is equally 

 active in all climates, and wiH do work of any kind : 

 it is a water-pumper, a miner, a sailor, a cotton-spin- 

 ner, a weaver, a blacksmith, a miUer, a printer, and is 

 indeed of all occupations ; and a small engine in the 

 character of a steam pony may be seen dragging after 

 it, on an iron rail-way, a hundred tons of merchandise 

 or a thousand persons with the speed of the wind." 



Steam-engines have been much used on large farms 

 in England for thrashing, grinding the feed of animals, 

 cutting fodder, and for other purposes. They have been 

 less used here, but may prove useful for large estab- 

 lishments, where the teams for ordinary tillage are in- 

 sufficient for stationary labor. 



More difficulty exists in their use for plowing, in con- 

 sequence of the labor and expense of moving frequent- 

 ly so heavy a machine, and the still greater difficulty 

 of using a locomotive power like that on rail-roads on 

 the soft surfaces of farms. 



EXCEPTION TO EXPANSION BY HEAT. 



A striking exception to the general law of expansion 

 by heat occurs in the freezing of water.*' During its 

 change to a solid state, it increases in bulk about one 

 twelfth, and this expansion is accompanied with a 

 great force. The bottoms of barrels are burst out, and 

 cast-iron kettles are split asunder, when water is suf- 

 fered wholly to freeze in them. Lead pipes filled with 



* There are a very few other substances which expand on passing 

 from a liquid to a solid state. 



