A portion of the work which necessarily occupied a very large amount of time was the painting, which was necessary for the preservation of all the parts, as well as for their appearance; and when it is considered that every portion required to be gone over four times, it must be evident that it was highly desirable to adopt some means for facilitating the operation. It was found that the sash-bars of the roof, being in short lengths and of small dimensions, could readily be operated upon by some mechanical contrivance. [Illustration: THE SASH-BAR PAINTING-MACHINE.] A wooden trough was made sufficiently long to receive the sash-bars, and this was filled with paint; a number of the bars were then put into it, and upon being taken out separately, they were passed through a frame into which a set of brushes were fixed in such a manner as to clear off all the unnecessary paint. Two small brushes, placed where the bar first entered the frame, cleared out the grooves. One workman pushed the bar in at one end of the frame, which was about two feet six inches long, and another drew it out at the other end, where a trough was placed to receive any droppings of paint. The bars were then stacked upright, until they were sufficiently dry for the next coat. The first coat only was put on by this apparatus, the second being done in the ordinary manner, and the last not till after the work was all fixed in its place. By means of this apparatus a workman could perform at least ten times the amount of work done in the ordinary way. [Illustration: THE FRAME-WORK WITH BRUSHES.] The finishing the painting of the various parts of the roof internally, after they had been put together, was very ingeniously managed, so that while the workmen were able to work with ease to themselves, the scaffolding on which they stood required no supports from the ground, where they would have been much in the way of other operations; loops of wrought-iron were hooked on to the roof-trusses, and by means of these a perfect cloud of scaffold-boards was suspended, enabling between 400 and 500 men to be at work at one time. The roof of the main avenue, particularly, presented a very singular appearance, as nearly one half of the entire length was thus covered at one time, and a crowd of painters were at work over the heads of many, perhaps unconscious exhibitors, who were arranging their goods undisturbed below. The Hand-rail Machine. One of the mechanical contrivances which were put up on the ground during the works, for saving labour and increasing the rapidity of production, remains to be mentioned; it was contrived for turning out the rounded mahogany hand-rail for the gallery railing as well as that for the staircases.