HISTORY OF ENGINEERING.

Book I.

348

500 tons, and by Mr. Morton’s principle this was reduced to 3/., without any riskwhatever.

A durable and substantial slip may be constructed, under ordinary circumstances, at thetenth part of the expense of a dry dock; and the apparatus employed may be moved fromone place to another. The vessel may be hauled up at the rate of feet per minute, by6 men to every 100 tons, so that the expense of taking up and launching a vessel of 500tons does not exceed 60s.

Ptterheady is situated on the most easterly point of Scotland . The town is built uponthe edge of an extensive bay, which affords to the vessels frequenting this coast a very

CftAVlNO fj

PETERHEAD HARBOl’

secure anchorage. Besides the old south harbour with its south pier, west jetty, andballast quay, there is a new harbour formed to the north, with a capacious graving-dock,excavated out of Green Island. The north jetty is carried out 470 feet, and its interiorwall was constructed on caissoons, as was the jetty-head which bears to the west, in length80 feet. This portion in 1819 was partly destroyed by the violence of the sea, and hassince been reconstructed upon a broader and firmer foundation.

Peterhead, so famous for its sea bathing, had its harbour considerably deepened bySmeaton , who recommended blasting 30,000 cubic yards of rock, but this operation has notbeen attended with the success that was expected: wooden boxes or cases were made useof by the workmen employed for this purpose; these movable cofferdams had occasionallythe water pumped out of them, and enabled the operation to be carried on at all timeswithout difficulty.

There is 18 feet water at the entrance at the top of an ordinary spring tide, but only14 feet at the eastern extremity of the pier.

The granite found here, called by the people who work it Pacey Whin, is the bestmaterial for building that can be obtained; it is scattered over the whole face of thecountry in large irregular lumps, and is so hard that it resists the finest tempered edgetool; but is admirably split into blocks of any size required, by the masons accustomed tothe work, who are perfectly aware that they cannot split the stone in any other directionthan that of its natural “ greet,” which they ascertain with great facility, and with suchcertainty, as seldom to be mistaken. After it is split they draw a straight line in thedirection of the “ greet,” and then sink a row of holes along it with a weighty hammer,having blunt points at both ends, and highly tempered; with this pick they unite the holesand form grooves, into which they place a wedge made of the best steel, with a point cutover square, so as to leave a triangular cavity below it; they then strike the wedges insuccession with a heavy hammer along the whole line, till the stone splits asunder; thefissure going through to the bottom of the stone, in the direction of the line first markedout, cleaving it into two parts, nearly as straight, though not so smooth, as if cut with asaw. When the stone is cut into a number of slabs, they are split into lengths at right