The problem was to find a material for the filament which would give a bright light and which, would, at the same time, be durable, and with this end in view, hundreds and hundreds of different filaments were tried. The difficulties in the way of this experimenting were enormous, since the light only burns when in a vacuum, and the instant the vacuum is impaired, out it goes. At one time, all the lamps he had burning at Menlo Park, about eighty in all, went out, one after another, without apparent cause. The lamps had been equipped with filaments of carbon and had burned for a month. There seemed to be no reason why they should not burn for a year, and Edison was stunned by the catastrophe. He began at once the most exhaustive series of experiments ever undertaken by an American physicist, remaining in his laboratory for five days and nights, dining at his work bench on bread and cheese, and snatching a little sleep occasionally, when one of his assistants was on duty. It was finally discovered that the air had not been sufficiently exhausted from the lamps. Again success seemed in sight, but soon the lamps began acting queerly again. Worn out with fatigue and disappointment, Edison took to his bed. Ultimate failure was freely predicted, and the price of gas stock rose again. In five months, the inventor had aged five years, but he was not yet ready to give up the fight. And at last it was won, and the incandescent lamp placed on the market. It has not displaced gas, as some people thought it would, but it is the basis of a business which made the inventor sufficiently rich to realize his great ambition of building himself the finest laboratory in the world; where the most expert iron-workers, wood-workers, glass-blowers, metal-spinners, machinists and chemists in the world find employment. Every known metal, every chemical, every kind of glass, stone, earth, wood, fibre, paper, skin, cloth, may be found in its store-rooms, ready for instant use. The library contains one of the finest collections of scientific books and periodicals to be found anywhere. These are the tools, and with them Edison is constantly at work upon a great variety of problems. The first thing he turned his hand to after his installation in his new laboratory was the phonograph. The patient thought and experiment, extending over many years, lavished on this wonderful invention are almost unbelievable. The idea had come to him years before, when he had worked out an instrument that would not only record telegrams by indenting a strip of paper with the dots and dashes of the Morse code, but would also repeat the message any number of times by running the indented strip of paper through it.