laughs and goes back to simpler matters. I watched him for a few moments before presenting myself. After a long look at his bottle, held up against the light, he put it down again on the table before him, and resting his head between his hands, both elbows on the table, he peered down at the bottle as if he expected it to say something. Then, after a moment's brown study, he would seize it again, give it a shake, as if to shake its secret out, and hold it up to the light. As pantomime nothing could have been more expressive. That liquid contained a secret it would not give up, but if it could be made to give it up, Edison was the man to do it, as a terrier might worry the life out of a rat. [Illustration: Edison's Menlo Park Electric Locomotive (1880).] The secret of his success might well be "Persistency, more persistency, still more persistency." One of his foremen relates that once in Newark when his printing telegraph suddenly refused to work, he locked himself into his laboratory, declaring that he would not come out till the trouble was found. It took him sixty hours, during which time his only food consisted of crackers and cheese eaten at the bench; then he went to bed and slept twenty hours at a stretch. At another time, during the height of the first electric-light excitement, all the lamps he had burning in Menlo Park, about eighty in all, suddenly went out, one after another, without apparent cause. Everything had gone well for nearly a month and the great success of the experiment had been published to the world. If the lamps, with their carbon filaments of charred paper would burn for a month there seemed to be no reason why they should not burn for a year, and Edison was stunned by the catastrophe. The trouble was evidently in the lamps themselves, for new lamps burned well. Then began the most exciting and most exhaustive series of experiments ever undertaken by an American physicist. For five days Edison remained day and night at the laboratory, sleeping only when his assistants took his place at whatever was going on. The difficulties in the way of experimenting with the incandescent lamp are enormous because the light only burns when in a vacuum. The instant the glass is broken, out it goes. Edison's eyes grew weak studying the brilliant glow of the carbon filament. At the end of the five days he took to his bed, worn out with excitement and sick with disappointment. During the last two days and nights he ate nothing. He could not sleep, for the moment he left the laboratory and closed his eyes some new test suggested itself. Neither was there much sleep for his faithful force. Ordinarily one of the most considerate of men, he seemed quite surprised when rest and refreshments were sometimes suggested as in order after fifteen hours' incessant work. The trouble was finally discovered to be one that time alone could have proved. The air was not sufficiently exhausted from the lamps. To