412 PILE-DRIVING BY STEAM. CHAP. XVIII. 



system, the pile was driven by a comparatively small 

 mass of iron descending with great velocity from a 

 considerable height the velocity being in excess and 

 the mass deficient, and calculated, like the momentum 

 of a cannon ball, rather for destructive than impulsive 

 action. In the case of the steam pile-driver, on the 

 contrary, the whole weight of a heavy mass is delivered 

 rapidly upon a driving-block of several tons weight 

 placed directly over the head of the pile, the weight 

 never ceasing, and the blows being repeated at the rate 

 of a blow a second, until the pile is driven home. It is 

 a curious fact, that the rapid strokes of the steam-hammer 

 evolved so much heat, that on many occasions the pile- 

 head burst into flames during the process of driving. 

 The elastic force of steam is the power that lifts the 

 ram, the escape permitting its entire force to fall upon 

 the head of the driving block ; while the steam above 

 the piston on the upper part of the cylinder, acting as a 

 buffer or recoil-spring, materially enhances the effect of 

 the downward blow. As soon as one pile was driven, 

 the traveller, hovering overhead, presented another, and 

 down it went into the solid bed of the river, with as 

 much ease as a lady sticks pins into a cushion. By the 

 aid of this formidable machine, what was formerly 

 among the most costly and tedious of engineering 

 operations, was rendered simple, easy, and economical. 



When the piles had been driven and the coffer-dams 

 formed and puddled, the water within the enclosed 

 space was pumped out by the aid of powerful engines, 

 so as, if possible, to lay bare the bed of the river. Con- 

 siderable difficulty was experienced in getting in the 

 foundations of the middle pier, in cons'equence of the 

 water forcing itself through the quicksand beneath as 

 fast as it was removed. This fruitless labour went on 

 for months, and many expedients were tried. Chalk 

 was thrown in in large quantities, outside the piling, 

 but without effect. Cement concrete was at last put 



