From the very important office which the girders perform throughout the building, but more particularly those supporting the galleries, it was of the utmost importance that, previously to their being fixed in their places, the soundness of the casting should be proved; for it could hardly be expected that so large a number of girders could be produced without some of them being defective. The ordinary means of testing girders, by loading them with weights, would have occupied far too much time; and therefore an ingenious apparatus was devised by Mr. C. H. Wild for this purpose, by the use of which the testing of a girder occupied but a few minutes. [Illustration: FRAME AND HYDRAULIC PRESS FOR TESTING THE GIRDERS.] It consisted of a very strong cast-iron frame rather longer than the girder, the bottom of which was formed by two fixed beams placed eight inches apart, and supported a few inches above the ground. At each end of these a cast-iron standard was firmly bolted between them and rose to a height rather greater than the depth of the girder to be tested; on the inner faces of these standards two "shoulders" were formed, which received the projections cast on the ends of the girder, as before mentioned. Between the fixed beams below, at two points dividing the whole length into three equal parts, were placed strong cylinders, with rising pistons connected with a forcing-pump, together with which they formed a Bramah's hydraulic press. A girder being placed in this frame, in an inverted position, the force applied by means of the pistons rising from the cylinders acted upon it precisely at those points, and in the same manner, as the load from the gallery or the roof would do when afterwards fixed in its place. The essential parts of the Bramah's press may be thus briefly described. It consists of two cylinders, the diameter of one being considerably larger than that of the other. The smaller cylinder is fitted with a solid plunger or piston, by means of which water may be forced from it into the larger; this being also fitted with a rising piston, the force is communicated by it to the weight which it is desired to raise. The power obtained by means of this apparatus arises from the distributive power of fluids and the practical incompressibility of water, and it is proportioned to the difference of the diameters of the two cylinders; so that if a pressure of one pound per square inch be applied on the surface of the piston in the smaller cylinder, and the piston in the larger cylinder present a surface ten times greater, the power is multiplied by that number; whilst, in addition, the lever power used in applying the pressure to the smaller piston is obtained. The cylinders are fitted with valves, so arranged as to prevent the return of the water from the larger to the smaller, while the apparatus is in action, and thus the power is accumulated in the former.