HE subject of the strength and stability of the building is one on which considerable anxiety has been felt, both by the public at large and by those professional bodies more capable of forming a correct judgment upon it. In the prolonged discussion which followed the reading of Mr. Wyatt's paper at the Institution of Civil Engineers, many points of objection were raised which seemed at first sight of a very serious nature; but, in most cases, the answers that were given to them were perfectly satisfactory. The two greatest difficulties raised were, firstly, the enormous surface presented by the exterior to the pressure of the wind, with apparently but a slight power of resistance; and, secondly, the construction of the galleries, which, it was thought, would not be able to resist the vibratory motion likely to be produced by great numbers of people walking upon them. The results of several calculations were adduced on the occasion alluded to in support of the objections on the first point; but perhaps the best answer that could be given to them was the circumstance mentioned by Mr. Fox—that on the 5th of that month (January) the pressure of the wind, which blew a perfect gale, was not only much above the average, but very nearly reached the greatest amount known within a considerable period in London—about 25lbs. per square foot; and that as the building, although in an incomplete state, had resisted that pressure without receiving any injury, it was fair to conclude that, when finished, it would be able to sustain the greatest force which the wind could be reasonably expected to exert upon it.
The question of the strength of the galleries was one of even greater importance than the other, as, in case of any failure in that part of the building, human life must almost inevitably have been sacrificed to a great extent. It was therefore deemed necessary to ascertain, as far as was practicable, by experiment, that their strength was abundantly sufficient; and in Mr. Wyatt's paper, as printed, the following description of the experiments instituted for this purpose will be found.
N the interval between the reading of this paper and its going to press a series of experiments have been tried to ascertain the action of these galleries under the strain of a moving load. A complete bay, twenty-four feet square, was constructed, raised slightly from the ground, consisting of the four cast-iron girders, with the connecting-pieces at the angles, and on this the timbers and boards of the flooring. Rows of planks the full width of the platform led up to it and down from it, so that a body of men as wide as the gallery might be able to march up and down in close rank.
"The area of the platform was first covered over with labourers packed as closely together as possible; but no action of walking, running, or jumping that 300 men could perform did any injury whatever to it, and the greatest deflection of the girders did not exceed a quarter of an inch. Soldiers of the corps of Royal Sappers and Miners were then substituted for the contractors' men; and although the perfect regularity of their step in marking time sharply appeared a remarkably severe test, a minute examination of the construction after the completion of the experiments showed that no damage whatever had been done by their evolutions.
"But as the Commissioners were deeply impressed with the necessity of thoroughly convincing the public, who should visit the Exhibition, that they might feel perfectly secure in every part of the building, it was deemed desirable to apply a still further test to the actual galleries as they stand; as it might perhaps be said that the single bay which had been experimented upon was not similarly circumstanced to those forming parts of the building.
