A glance at the book-shelves affords a revelation of the subjects in which Edison is interested, for the titles of the volumes include astronomy, botany, chemistry, dynamics, electricity, engineering, forestry, geology, geography, mechanics, mining, medicine, metallurgy, magnetism, philosophy, psychology, physics, steam, steam-engines, telegraphy, telephony, and many others. These are not all of Edison's books by any means, for he has another big library in his house on the hill. Turning to pass out of the library, one's attention is arrested by a cot standing in one of the alcoves near the door. Sometimes during long working hours Mr. Edison will throw himself down for a nap. He has the ability to go to sleep instantly, and, being deaf, noises do not disturb his slumber. The instant he awakes he is in full possession of his faculties and goes "back to the job" without a moment's hesitation. Immediately outside the library is the famous stock-room, about which much has been written. Edison planned to have in this stock-room some quantity, great or small, of every known substance not easily perishable, together with the most complete assortment of chemicals and drugs that experience and knowledge could suggest. His theory was, and is, that he does not know in advance what he may want at any moment, and he planned to have anything that could be thought of ready at hand. Thus, the stock-room is not only a museum, but a sample-room of nature, as well as a supply department. At first glance the collection is bewildering, but when classified is more easily comprehended.