In respect to the decoration of the interior, a keen controversy has been waged. The fact of iron being the material of construction renders it necessary that it should be painted to preserve it from the action of the atmosphere. On the one hand, it is said that the fact that the structure is metallic should be indicated by the decoration, otherwise the whole will have no more appearance of stability than an arbor of wicker-work. Those who take this view recommend that the interior should be bronzed. On the other hand, those to whom the decoration is intrusted affirm that the object of using color is to increase the effect of light and shade. If the whole were of one uniform dead color the effect of the innumerable parts of which the building is composed, all falling in similar lines, one before the other, would be precisely that of a plane surface; the extended lines of pillars presenting the aspect of a continuous wall. In order to bring out the distinctive features of the building various colors must be used; and experiments show that a combination of the primary colors, red, blue, and yellow, is most pleasant to the eye. The best means for using these is to place blue, which retreats, upon the concave surfaces, yellow, which advances, upon the convex ones, reserving red for plane surfaces. But as when these colors come in contact each becomes tinged with the complementary color of the other--the blue with green, the red with orange--a line of white is interposed between them. Applying these principles, the shafts of the columns are to be yellow, the concave portions of their capitals blue, the under side of the girders red, and their vertical surfaces white. Among all the wonders of the Crystal Palace nothing is more wonderful than its cheapness, and the rapidity of its construction. Possession of the site was obtained on the 30th of July; in a period of only 145 working-days the building was to all intents and purposes completed. As to cheapness it costs less per cubic foot than an ordinary barn. If used only for the Exhibition, and at its close returned to the contractors, the cost will be nine-sixteenths of a penny a foot; or, if permanently purchased, it will be one penny and one-twelfth. Thus: The solid contents are 33,000,000 cubic feet; the price if returned is £79,800, if retained £150,000. This simple fact, that a building of glass and iron, covering eighteen acres, affording room for nine miles of tables, should have been completed in less than five months from the day when the contract was entered into, at a cost less than that of the humblest hovel, opens a new era in the science of building.