Thomas A. Edison is sometimes spoken of rather as a master mechanic than as a master inventor or discoverer, and with regard to some of his work--I might even say most of it--this characterization holds true. Edison's fame is chiefly associated in the popular mind with the electric light. Yet it is perfectly well known to every student of the matter, that in all that he has done toward making the electric light a useful every-day--or perhaps I should say every-night--affair, he has simply made practicable what other men had invented or discovered before him. The fundamental discovery upon which the incandescent electric lamp is founded--that a wire of metal or other substance if heated to incandescence in a glass bulb from which the air has been exhausted will give light for a longer or shorter time, according to the character of the apparatus and the degree to which a perfect vacuum has been effected in the bulb--this dates from the first half of the century. As early as 1849 Despretz, the French scientist, described a series of experiments with sticks of carbon sealed in a glass globe from which air had been exhausted. When a powerful current was passed through the carbon filament it became luminous and remained so for a short time. This was, perhaps, the first of a long line of similar experiments in which a number of American physicists--Farmer, Draper, Henry, Morse, and Maxim among them--took part. But notwithstanding the labors of a score of experts in Europe and this country, the incandescent electric light--the wire in a glass bulb exhausted of its air--remained a laboratory curiosity up to the time, fifteen years ago, when Edison took hold of it. It gave light only for a short time and was too expensive a toy for practical use. The carbon burned out or disintegrated, and the lamp failed. Edison took hold of the mechanical difficulties of the problem. With a patience, an ingenuity, a fertility of device in which he stands alone, he got to the bottom of each radical defect and remedied it. The lamp would not burn long because the platinum wire used gave out, partly because platinum was not fitted for the work, fusing at too low a temperature. Edison substituted carbonized strips of paper. These in turn failed, and he found a species of bamboo that answered. The lamp would not burn because air still remained in the little bulbs notwithstanding the most careful manipulation with Sprengel pumps to exhaust the air. Edison invented new pumps and devices by which the air, down to one millionth part, was excluded. The lamp cost too much to operate, because large copper wires were needed to carry the current, and the generators used up steam power too fast. Edison devised new forms of conductors and generators. All such work called more for mechanical ingenuity than for actual invention. No new principles were involved--merely the better adaptation of known methods. Given a perfect