Chap. XII.
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which compose this column without the use of scaffolding, by means of a series of tall sparsjoined together, like the mast of a ship ; the lowest being fixed firmly in the ground,and braced by diagonal pieces, as well aslashed and strutted to the lower part of theshaft. A gaff, with a jaw at the lower end,was then slung in the throat by a strongrope or chain, so as to work round theupper spar in the jaw prepared for it; fromthe ends of this gaff, blocks and a fall weresuspended, which, by raising or depressingthe point of the gaff, commanded everyportion of the work. The stones were raisedby means of crabs turned by winches, andthe whole work was terminated in a shorttime.
Obelisk on the Whitaw Eskdale, erectedto the memory of Sir John Malcolm , is inheight 100 feet above the foundation; it isbuilt with a hollow space in the middle,with whole courses occasionally passingthrough ; in these a large circular hole wasleft, and the crane was raised after the com-pletion of each course. It was thusformed : — In the lower hole was inserteda pole 10 inches in diameter, and 40 feetin length ; the next hole above served as astay, whilst the upper one supported thewhole weight, a collar of hard wood beingfirmly fixed around the pole. Beneath thiscollar were introduced 17 metal balls about3^ inches in diameter, which running ingrooves prepared for them enabled the poleeasily to turn round. At the top of thepole, and placed crossways, was mortised abeam 12 inches square, and 12 feet in length,strengthened by diagonal iron bars andstraps.
The stones were raised by a crab winch,the rope passing over a pulley at each endof the horizontal beam, and moved to theirsituation by a traversing carriage, which Fig. 1531.
worked on the beam by means of a small crab and pulleys.
We cannot perhaps better illustrate our present subject than by giving the account ofthe manner in which the obelisk in front of St. Peter’s at Rome was raised by the celebratedDomenico Fontana ; its weight was estimated by that architect as equal to 993,537pounds ; the height is 180 palms, but without the apex 77’2 English feet; the transversesection at the middle contains an area of 7*6 superficial feet; the solid content may, there-fore, be taken at upwards of 166 cubic yards, weighing about 332 tons ; if to this be added4 tons for the weight of the apex, the whole weight of the obelisk raised is upwards of 336tons. The length of each of the sides at bottom is 12£ palms, and at top palms, thepalm being equal to 8-7 English inches: 46 cranes, 600 men, and 140 horses wereemployed in removing it, and the timber, ropes, and iron made use of cost 20,000 crowns.The operations for removing it, which were conducted with the greatest skill, were asfollows: —
A scaffold, called a castellum or shears, was first constructed, 7 feet higher thanthe top of the obelisk when mounted on the pedestal. The eight principal timbers, four oneach side, were 89 feet in height from the foundation; they were each built of oak andwalnut, four beams in thickness, and banded at every 9 feet with strong iron hoops, andbolted together in several parts. The whole was so arranged that it could be easily putup or taken down, to suit the several positions in which the obelisk might be placed :wherever this castellum was to be used, 4 holes 3 feet square were prepared in a platformof travertine stone, into which the four posts were dropped and secured.
The obelisk was cased over with double mats to protect it from injury; was then coveredwith two-inch plank, and longitudinal iron bars, 4 inches in breadth, were attached to it,three on each of the four sides; these, connected together by nine iron hoops, served toattach the tackle ; this coating of mat, wood, and iron was estimated to weigh as much asone-twelfth of the obelisk. Thus entirely covered, the obelisk was lifted from the pedestal
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DEVONPOilT DERRICK.