The store-rooms contain all the material needed. Four store-keepers are employed to keep the supplies, valued at $100,000, in order and ready for use at a moment's notice. Each article is put down in a catalogue which shows the shelf or bottle where it may be found. Every known metal, every chemical known to science, every kind of glass, stone, earth, wood, fibre, paper, skin, cloth, is to be found there. In making up the chemical collection an assistant was kept at work for weeks going through the three most exhaustive works on chemistry in English, French, and German, making a note of every substance mentioned, and this list constituted the order for chemicals, an order, by the way, which it required seven months to fill. In the glass department, for instance, there is every known kind of glass, from plates two inches thick to the finest, film, and if anything else in the way of glass is needed, the glass-workers are there to make it. This stupendous collection of material, filling one floor, is intended to guard against annoying delays that might occur at critical times for want of some rare material. In 1885, when working upon an apparatus for getting a current of electricity directly from heat--the thermo-electric generator--Edison's work was brought to a standstill for want of a few pounds of nickel, an article not then to be found in any quantity in this country. The store-room was organized to avert such delays. The library is the only part of the main building that shows any attempt at decoration. It is a superb room, 60 feet by 40, with a height of 25 feet. Galleries run around the second story. At one end is a monumental fireplace, and in the centre of the hall a fine group of palms and ferns. The room is finished in oiled hard wood and lighted by electricity. Fine rugs cover the floors. The shelves contain nothing but scientific works and the files of the forty-six scientific periodicals in English, French, and German to which Edison subscribes. They are indexed by a librarian as soon as received, so that Edison can see at a glance what they contain concerning the special fields in which he is interested.