Mr. Nasmyth subsequently applied the principle of the steam-hammer in the pile driver, which he invented in 1845. Until its production, all piles had been driven by means of a small mass of iron falling upon the head of the pile with great velocity from a considerable height,--the raising of the iron mass by means of the "monkey" being an operation that occupied much time and labour, with which the results were very incommensurate. Pile-driving was, in Mr. Nasmyth's words, conducted on the artillery or cannon-ball principle; the action being excessive and the mass deficient, and adapted rather for destructive than impulsive action. In his new and beautiful machine, he applied the elastic force of steam in raising the ram or driving block, on which, the block being disengaged, its whole weight of three tons descended on the head of the pile, and the process being repeated eighty times in the minute, the pile was sent home with a rapidity that was quite marvellous compared with the old-fashioned system. In forming coffer-dams for the piers and abutments of bridges, quays, and harbours, and in piling the foundations of all kinds of masonry, the steam pile driver was found of invaluable use by the engineer. At the first experiment made with the machine, Mr. Nasmyth drove a 14-inch pile fifteen feet into hard ground at the rate of 65 blows a minute. The driver was first used in forming the great steam dock at Devonport, where the results were very striking; and it was shortly after employed by Robert Stephenson in piling the foundations of the great High Level Bridge at Newcastle, and the Border Bridge at Berwick, as well as in several other of his great works. The saving of time effected by this machine was very remarkable, the ratio being as 1 to 1800; that is, a pile could be driven in four minutes that before required twelve hours. One of the peculiar features of the invention was that of employing the pile itself as the support of the steam-hammer part of the apparatus while it was being driven, so that the pile had the percussive action of the dead weight of the hammer as well as its lively blows to induce it to sink into the ground. The steam-hammer sat as it were on the shoulders of the pile, while it dealt forth its ponderous blows on the pile-head at the rate of 80 a minute, and as the pile sank, the hammer followed it down with never relaxing activity until it was driven home to the required depth. One of the most ingenious contrivances employed in the driver, which was also adopted in the hammer, was the use of steam as a buffer in the upper part of the cylinder, which had the effect of a recoil spring, and greatly enhanced the force of the downward blow.