This design was then laid before the contractors, Messrs. Fox and Henderson, who at once determined to submit a tender for the construction of a building in accordance with it. In a single week, they had calculated the amount and cost of every pound of iron, every pane of glass, every foot of wood, and every hour of labor which would be required, and were prepared with a tender and specifications for the construction of the edifice. But here arose a difficulty. The committee had advertised only for proposals for carrying out their own design; but, fortunately, they had invited the suggestion on the part of contractors, of any improvements upon it; and so Mr. Paxton's plan was presented simply as an "improvement" upon that of the committee, with which it had not a single feature in common. This, with certain modifications, was adopted, and the result is the Crystal Palace--itself the greatest wonder which the Exhibition will present--the exterior of which is represented in our accompanying Illustration. The building consists of three series of elevations of the respective heights of 64, 44, and 24 feet, intersected at the centre by a transept of 72 feet in width, having a semicircular roof rising to the height of 108 feet in the centre. It extends in length 1851 feet from north to south, more than one-third of a mile, with a breadth of 456 feet upon the ground; covering 18 superficial acres, nearly double the extent of our own Washington-square; and exceeding by more than one half the dimensions of the Park or the Battery. The whole rests upon cast-iron pillars, united by bolts and nuts, fixed to flanges turned perfectly true, so that if the socket be placed level, the columns and connecting-pieces must stand upright; and, in point of fact, not a crooked line is discoverable in the combination of such an immense number of pieces. For the support of the columns, holes are dug in the ground, in which is placed a bed of concrete, and upon this rest iron sockets of from three to four feet in length, according to the level of the ground, to which the columns are firmly attached by bolts and nuts. At the top, each column is attached by a girder to its opposite column, both longitudinally and transversely, so that the whole eighteen acres of pillars is securely framed together.