490 



THE APPLICATIONS OF PHYSICAL FORCES. [BOOK iv. 



mills, fixed engines are always employed, and sometimes movable 

 ones in addition : these give and distribute motion to all the works by 

 means of cogs or straps. Planing, drilling, mortising, boring, screw- 

 making, polishing metal surfaces are all clone by the force of steam, 

 and it is difficult to know which to admire most in these great opera- 



FIG. 329. A steam block-hammer. 



tions the power of the engine, or the docility with which it adapts 

 itself to any kind of work. 



Is it not something marvellous to see the machine work steel and 

 iron with as great ease as a workman handles wood, be he carpenter 



