SCAFFOLDING. In ordinary buildings the scaffolding requires very little notice. Poles are erected in a vertical position a few feet from the walls, their lower ends being inserted in the ground. Wherever a platform is required for the workmen, a horizontal pole is tied to the uprights, parallel with the wail ; and from this horizontal pole cross-pieces extend to the wall, into which their ends are received, to support.a flooring of planks. As the building rises, the scaffold is strengthened by diagonal poles ; and the several poles are fastened by ropes, In the erection of important buildings of stone, a very convenient kind of scaffold has been recently adopted, consisting of large squared timbers well framed together, and terminating at the top in horizontal beams. Such a framing is erected on each side of the wall, unconnected with it, and rails are laid on the top beams, on which runs a carriage, ca pable of being moved by means of a winch handle connected with the wheels. The carriage itself consists of a frame supporting another railway at right angles with that on which it runs ; and on the upper railway is a smaller carriage, which supports tackle suita ble for raising the stones. By this arrange ment a stone may be lifted up, and moved, by the combined action of the two railways, to any point required on the wall.
In bridge building and similar works, the centering of arches is a peculiar kind of scaf folding ; it is the wooden support or mould on which the arch rests While building. A cen tering usually consists of a number of distinct frames, resembling the trusses of a roof, placed equidistant from each other in vertical planes, and covered with a series of planks or beams of timber called bridging-joists, laid at right angles with the frames or trusses. This boarding or covering of bridgings forms a con vexity coinciding with the internal concavity of the intended arch. For small arches the
centering is usually covered with planks ; but in large works bridging-joists, one laid for each course of arch-stones, are preferred, these being kept at the proper distance apart by blocks placed between them. The whole structure is stiffened by crossbars to keep the trusses equidistant and parallel to each other.
Mr. Hughes has invented a scaffolding, which he used for repairing the interior of a dome at Manchester. It consists of a vertical pole erected in the centre of the dome, to which is connected a framework, supporting a kind of ladder, corresponding with the form of the interior of the dome, and mounted on wheels, so that it may be moved round to any part of it, the vertical pole serving as an axis. Mr. Slacks, a mason, has invented a scaffolding for building an obelisk without scaffolding of the ordinary description. This simple and ingenious machinery was used in erecting an obelisk of sandstone, 100 feet high, not inclu ding the foundation, on the summit of a mountain called Whitaw, in Dumfriesshire, in honour of the late Major-General Sir John Malcolm. The Society of Arts rewarded the inventor with their gold Isis medal in 1837.
The finest scaffolding ever invented, per-, baps, is that which now surmounts the Victoria tower at the New Houses of Parlia ment. It is made to travel upwards as the work progresses ; and it revolves on a central axis, so that four extended arms of scaffolding may be brought over every part of the tower in turn.
If the scaffolding just mentioned is the most complete, perhaps that by which Messrs. Fox and Henderson have built the Crystal Palace is the most simple—so simple, indeed, that it can hardly be called a scaffolding ; it is rather a system of ropes and pailleys.