484 THE APPLICATIONS OF PHYSICAL FORCES. [BOOK iv. 



fuel, wear and tear, and much lower centre of gravity. These 

 rollers are adapted for driving stonebreakers or other fixed machinery 

 most economically, when not required for rolling; and for use as 

 traction engines. 



VI. PORTABLE ENGINES. 



There remains to be examined a fourth type of steam-engines, 

 recently introduced, the use of which is continually increasing, and 

 which has no further resemblance to the locomotive than the name 

 and outside appearance. Locomobile is the term given by the French 

 to this class of engine. 



In reality, a locomobile is a fixed engine, but it is movable from 

 place to place. Relatively lighter and less cumbersome, it is pla.ced 

 like the locomotive on a framework and mounted on wheels. The 

 boiler, the machinery, the fly-wheel, are all arranged in such a way as 

 to require no more to set it working than supplying it with fuel and 

 lighting it. When the engine has done its work at one place, it is 

 taken to another, where its power is required, which is thus made use 

 of in two places removed from each other. The wheels of the locomo- 

 bile are not as in the locomotive the driving-wheels. They are 

 absolutely independent of the machinery, and have but one object : 

 that of allowing the engine to be drawn from place to place and 

 across fields. By putting in two horses this is the easiest thing in 

 the world. 



This is a power now universally employed. In agriculture, and 

 in industrial works, these locomobiles serve for many purposes, and 

 replace with advantage the labour of horses or men. 



In the construction of masonry of sufficient importance, locomo- 

 biles are employed to hoist the materials ; they move the hoists, they 

 turn the crushing-mills for making mortar, and are substituted for the 

 workmen who raise the monkeys for pile-driving, or who work the 

 cranes. Steam-cranes with movable engines may be frequently seen 

 at commercial or military ports. 



Locomobiles are employed for working the pumps fixed tem- 

 porarily for draining earthworks. One of them might be seen 

 at work in front of the Louvre during the siege of Paris ; it 



