20 



THE APPLICATIONS OF PHYSICAL FORCES. [BOOK i. 



metre or 1 20. When the piles, already driven to a certain depth, 

 only give way slowly under the strokes of this machine, the mechanical 

 pile-drivers are employed to finish the work. With these the weight 

 can be lifted to a height varying from 2 m 5 to 5 or 6 metres. The 

 useful effect, which depends on the height of the fall, is therefore 

 much more considerable. The weight of the 

 monkey varies from 300 to 600 kilogrammes, 

 and the number of men necessary to the work- 

 ing of the manual pile-drivers reaches 

 sometimes as many as forty. Recently steam 

 has been applied to these machines, as seen 

 in Plate I. ; a portable steam-engine giving 

 motion to the machine. It does not appear 

 that steam has hitherto been used directly for 

 pile -driving, yet the difficulties of its appli- 

 cation for that purpose do not appear to be 

 insurmountable. A fixed boiler at the base 

 of the machine, and a steam-hammer capable 

 of being fixed at any height and connected 

 with the boiler by flexible tubing, if neces- 

 sary, would appear to be all that is required 

 for the application of steam for this purpose. 

 An American invention has recently increased 

 the force of -the fall by causing the monkey 

 at the moment the detent is opened to ex- 

 plode a small charge of gunpowder. 



The steam-hammer, which is a kind of monkey used in forging 

 metals, is, like the pile-driver, an application of the force of gravity. 

 We only speak of them here in passing, as we intend to refer again 

 to them in the chapters devoted to steam. Here, indeed, we must 

 keep well before our minds one important application of the force 

 developed by a heavy mass in its fall, under the sole action of 

 weight. 



We must remark, in concluding, that all this force is not utilized 

 in producing the desired effect, which is the driving of the piles : a 

 part is transformed into heat, that is to say, into a molecular move- 

 ment common to both masses which are thus suddenly brought into 

 contact the monkey on the one side, and on the other the head of 



FIG. 4. Details of meclianis 

 the detent. 



