The accompanying figures illustrate this engine and my high-speed equivalent drawn to the same scale; it will be seen that the small engine occupies about one tenth of the floor space needed for the large one, and would cost less than ten per cent. of the money. It would also have a more nearly uniform motion, the impulses received by the crank being 300 per minute, against only 144 per minute received by both cranks of the large engine, besides which in the latter the full force of the steam is exerted at the commencement of each stroke and falls to nothing at the end, while in the smaller engine, by the inertia of the reciprocating parts, the forces exerted at the opposite ends of the stroke would be practically equalized. The reader will doubtless inquire, as Mr. Green did why, with these enormous advantages, does not everybody use the high-speed engines and every builder make them? [Illustration: The Corliss Engine Exhibited at the Centennial Exhibition.] [Illustration: Porter-Allen Engine Equal in Power to the Exhibited Corliss Engine.] At this exhibition the Bell telephone was first shown to a select company, among which were President Grant and Dom Pedro, the last emperor of Brazil. This exhibition was given on Sunday, that being the only day when silence could be had. Human speech, both in talking and singing, was transmitted through the whole length of the main building, about 1800 feet; it has since been transmitted somewhat further. The exhibitors of hand pumps all talked about the ease with which their own pumps could be worked; one man touched bottom in this respect. He had set his pump so that the spout was nearly on a level with the surface of the pool from which it drew its water; he boldly claimed that his pumps required no power at all. I was invited, as I suppose multitudes were, to take hold of the handle and see for myself that his claim was true. I never heard of but one man who I think would be satisfied with this demonstration; that was the engineering editor of the New York _Tribune_. Shortly before this he had published an account of a wonderful pump invented by a Mr. George, which he concluded by saying that the superiority of Mr. George’s pump lay in the fact that at each stroke not the whole column of water had to be lifted, but only that which was to be discharged. We had a waterfall maintained by a centrifugal pump, which received its water on one side only; the maker evidently knowing nothing about the method of balancing these pumps by admitting the water equally on the opposite sides.