e pile-driving. A temporary
staging was erected for the steam-engine and hammer apparatus, which
rested on two keels, and, notwithstanding the newness and stiffness of
the machinery, the first pile was driven on the 6th October, 1846, to a
depth of 32 feet, in four minutes. Two hammers of 30 cwt. each were kept
in regular use, making from 60 to 70 strokes a minute; and the results
were astounding to those who had been accustomed to the old style of
pile-driving by means of the ordinary pile-frame, consisting of slide,
ram, and monkey. By the old 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 almost as much ease as a lady sticks
pins into a cushion. By the aid of this powerful machine, pile-driving,
formerly among the most costly and tedious of engineering operations,
became easy, rapid, and comparatively economical.

When the piles had been driven and the coffer-dams formed and puddled,
the water within the enclosed spaces was pumped out by the aid of
powerful engines, so as, if possible, to lay bare the bed of the river.
Considerable difficulty was experienced in getting in the foundations of
the middle pier, in consequence 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 trie