66 ANNUAL OF SCIENTIFIC DISCOVERY. 



positions, was contemplated ; but, after a few trials, the ground was 

 found to consist of a compact mass of rag-stone, so that the mere atmos- 

 pheric action upon the piles, induced by a partial vacuum, would be 

 ineffective in such a situation. It was, therefore, decided that the pneu- 

 matic process should be reversed, so as to give each pile the character of a 

 diving-bell ; for which purpose one of the cylinders, seven feet in diameter, 

 and nine feet in length, had a wrought-iron bolt securely bolted to it, 

 through which two cast-iron chambers, D shaped in plan, with a sectional 

 area of six square feet, appropriately called air-locks, projected two feet 

 six inches above the top of the cylinder. The top of each air-lock was 

 provided with a circular opening, two feet in diameter, with a flap work- 

 ing on a horizontal hinge, and an iron door, with vertical hinges, below 

 the cover ; each air-luck was also furnished with two sets of cocks, the 

 one for forming a communication between the cylinders and the cham- 

 ber, the other between the chamber and the atmosphere. Compressed 

 air was supplied to the cylinder pile by a double-barreled pump, driven 

 by a six horse-power steam engine. At first the expelled water was 

 made to pass into the river, from beneath the lower edge of the pile ; 

 but when the stratum became so compact as to oppose a high degree 

 of resistance to the passage of the air, an outlet was formed through 

 the side of the uppermost cylinder, by the introduction of a pipe, having 

 the form of a syphon, the long leg of which reached to the bottom of a 

 pile, and was subject to the pressure of the condensed air on the surface 

 of the water within, whilst the short leg, leading into the river, had the 

 effect of relieving the amount of compression, providing a vacuum was 

 once obtained in the body of the syphon. Such an effect was readily 

 produced by connecting the summit with the exhaust side of the air- 

 pumps, by a pipe which could be opened or closed at pleasure. To 

 insure the downward motion of the pile, and to give it a weight which 

 should be at all times superior to the upward pressure, two stout trussed 

 timber beams were laid on the top of the cylinder, in a direction 

 suitable for bringing the adjacent piles into action as counterbalance 

 weights, by four chains passing over cast-iron sheaves. Two light 

 wrought-iron cranes vrere fixed inside the cylinder, the jibs of which 

 swept over the space between the air-locks and windlasses, inside, for 

 the purpose of hoisting the loaded buckets and lowering the empty 

 ones. 



The method followed in working the apparatus was found to be so 

 simple in detail as to be perfectly intelligible to all the workmen 

 employed. The pumps being set in motion, the flap of one of the air- 

 locks and the door of the other were closed ; a few strokes compressed 

 the air within the pile sufficiently to seal the joints, and whilst the 

 j tumping was in progress, the men passed through the air-locks to their 

 respective stations. When the water was shallow, the pile descended, 

 by scarcely sensible degrees, as fast as the excavation by hand permitted ; 

 but when the water was deep, the excavation was carried down full 14 

 inches below the edge of the pile, which then descended at once through 

 the whole space, as soon as the pressure was easxl off. 



