One of the secrets of Edison's great success is the ease with which he concentrates his mind. He is said to possess the faculty of leaving one thing and taking up another whenever he wills. He even carries on in his mind various trains of thought at the same time. The operations of his brain are imitated in his daily conduct, which is direct and simple in all respects. He is never happier than when engaged in the most absorbing and exacting mental toil. He dresses in a machinist's clothes when thus employed in his laboratory, and was long accustomed to work continuously for as long as he was so inclined without regard to regularity, or meals, or day or night. He is willing to eat his food from a bench that is littered with filings, chips and tools. To relieve strain and take a moment's recreation he is known to have bought a "cottage" organ and taught himself to play it, and to go to it in the middle of the night and grind out tunes for relaxation. He has a working library containing several thousand books. He pores over these volumes to inform himself upon some pressing idea, and does so in the midst of his work. No man could have made some of his inventions unaided by technical science and a knowledge of the results of the investigations of many others, and it has often been wondered how a man not technically educated could have seemed so well to know. There was a mistake. He _is_ educated; a scientific investigator of remarkable attainments. In thinking of the inventions of Edison and their value, a dozen of the first class, that would each one have satisfied the ambition or taken the time of an ordinary man, can be named. The mimeograph and the electric pen are minor. Then there are the stock printer, the automatic repeating telegraph, quadruplex telegraphy, the phono-plex, the ore-milling process, the railway telegraph, the electric engine, the phonograph. Some of these inventions seem, in the glow of his incandescent light, or with one's ear to the tube of the telephone he improved in its most essential part, to be too small for Edison. But nothing was too small for Franklin, or for the boy who played idly with the lid of his mother's tea-kettle and almost invented the steam-engine of today, or for Hero of Alexandria, who dreamed a thousand years before its time of the power that was to come. So was Henry's first electric telegraph the merest toy, and his electro-magnet was supported upon a pile of books, his signal bell was that with which one calls a servant, and his idea was a mere experiment without result. There was a boy Edison needed there then, whose toys reap fortunes and light, and enlighten, the world. The electric pen was in its day immensely useful in the business world, because it was the application of the stencil to ordinary manuscript, and caused the making of hundreds of copies upon the stencil idea, and with a printer's roller instead of a brush. The mimeograph was the same idea in a totally different form.