The cable carries eighteen trays, distributed at regular intervals. Each tray is capable of carrying a volume the size of the ordinary quarto, (say eleven inches by ten, and four inches thick), or its equivalent in smaller volumes. Larger books must be carried by hand down the elevator with which each stack is provided. The tray is of brass, made in the form of a hooked comb, the ends of the teeth being left free. The terminal cabinet and all the stack stories are provided with toothed slides, the teeth of which engage with those of the trays, and rake off or deliver the books, as the case may be. If one bends and slightly opens the fingers of both hands, and then draws the fingers of one through those of the other, the general principle of the arrangement will immediately be seen. The tray, however, can receive books only when going up, and can deliver them only when coming down. When a book is received by a slide it falls into a padded basket, ready to be taken to its place on the shelves or delivered to the reader. When the attendant desires to deliver a book to the Rotunda, he places it on the slide, and sets the latter so that it will be ready to meet the first tray which arrives. In returning books, the officer at the Distributing Desk must set a little lever on a dial at the number of the stack for which the book is intended. When the tray approaches the proper floor, the slide is automatically pushed out to receive the load. [Illustration: FULTON. BY EDWARD C. POTTER.]