864 Transactions of the American Institute. 



of the preceding blow had had time to subside, and therefore nearly 

 the whole force of its blow was employed in the displacement 

 beneath the pile. Li the other machines, the blows were given at 

 intervals of a minute, by which time the vibrations bad ceased, and 

 the material had partiallj' subsided around the pile, so that a con- 

 siderable portion of the force of the blow was consumed in over- 

 coming the friction along the sides, and in the removal by new 

 vibrations, leaving only a comparatively small portion of the force 

 to displace the earth at the bottom. 



This effect would probably be produced in nearly all descriptions 

 of earth, although it would be greater in loose and partially fluid 

 material than in clay or compact soil. 



The use of the Nasmyth machine demonstrates the value of quick 

 blows, not only in the economy of driving, but also in obtaining a 

 deeper penetration, which is often very desirable. 



The comparative cost of driving by the use of diflerent kinds of 

 power, is nearly as follows: 



By steam with the Nasmyth ram 5. 



" " ordinary machines 9. 



" horse-power with " " 12. 



" man-power — ^tread-wheel 15. 



« " cranks 20. 



And these sums represent cents per lineal foot of pile driven in 

 1846." 



With a reliable rule like that above furnished, the piles may bo 

 driven for a foundation, so that it shall be able to sustain in every 

 place, the load of the superstructure, even when very unequally 

 distributed. 



I have frequently observed foundations made when the piles 

 were driven without regard to these essential conditions — where, 

 if the support of the piles had been tested, some of them would be 

 found to have but one-tenth of the sustaining [)Ower of other con- 

 tiguous ones; so that in one place, a large expense has been wasted, 

 and in another the support was insufficient, and the structure was 

 in danger of being rained, or it is only saved from immediate 

 destruction by the strength of the grillage or of its inherent tena- 

 city, and is liable to fail at any moment. 



In rivers subject to rapid currents, the obstructions caused by 

 the piers greatly increase the velocity of the water over the river 

 bed, adjacent to the piles, and frequently removes the material from 



