In the construction of the building care has been taken to give to each part the stiffest and strongest form possible in a given quantity of material. The columns are hollow, and the girders which unite them are trellis-formed. The utmost weight which any girder will ever be likely to sustain is seven and a half tons; and not one is used until after having been tested to the extent of 15 tons; while the breaking weight is calculated at 30 tons. At first sight, there would seem to be danger that a building presenting so great a surface to the action of the wind, would be liable to be blown down. But from the manner in which the columns are framed together they can not be overthrown except by breaking them. Experiments show that in order to break the 1060 columns on the ground floor, a force of 6360 tons must be exerted, at a height of 24 feet. The greatest force of the wind ever known is computed at 22 pounds to the superficial foot; assuming a possible force of 28 pounds, and suppose a hurricane of that momentum to strike at once the whole side of the building, the total force would be less than 1500 tons--not one-fourth of the capacity of the building to sustain, independent of the bracings, which add materially to its strength. So that, if any reliance at all can be placed upon theoretical engineering, there can be no doubt as to the safety of the building. Entering at the main east or west entrance, we find ourselves in a nave 64 feet in height, 72 in breadth, and extending without interruption the whole length of the building, one-third of a mile. Parallel with this, but interrupted by the transept in the centre, are a series of side aisles of 48 and 24 feet in breadth, with a height of 44 and 24 feet. Over the centre of the nave swells the semicircular roof of the transept, overarching the stately trees beneath--a Brobdignagian green-house with ancient elms instead of geraniums and rose-bushes. The whole area of the ground floor is 772,784 square feet; and that of the galleries 217,100; making in all within a fraction of one million square feet; to which may be added 500,000 feet of hanging-space, available for the display of the products of human heads and hands. There are three refreshment rooms, one in the transept, and one near each end, around the trees which were left standing, where ices and pastry for the wealthy, and bread-and-butter and cheese for the poorer are to be furnished. No wine, spirits, or fermented liquors are to be sold; only tea, coffee, and unfermented drinks; pure water is to be furnished gratis to all comers by the lessees of the refreshment rooms.