THE MERCURY-VAPOR LIGHT OF PETER COOPER HEWITT "On an evening in January, 1902, a great crowd was attracted to the entrance of the Engineers' Club in New York city. Over the doorway a narrow glass tube gleamed with a strange blue-green light of such intensity that print was easily readable across the street, and yet so softly radiant that one could look directly at it without the sensation of blinding discomfort which accompanies nearly all brilliant artificial lights. The hall within, where Mr. Hewitt was making the first public announcement of his great discovery, was also illuminated by the wonderful new tubes. The light was different from anything ever seen before, grateful to the eyes, much like daylight, only giving the face a curious, pale-green, unearthly appearance. The cause of this phenomenon was soon evident; the tubes were seen to give forth all the rays except red,--orange, yellow, green, blue, violet,--so that under its illumination the room and the street without, the faces of the spectators, the clothing of the women, lost all their shades of red; indeed, changing the face of the world to a pale green-blue. "The extraordinary appearance of this lamp and its profound significance as a scientific discovery at once awakened a wide public interest, especially among electricians who best understood its importance. Here was an entirely new sort of electric light. The familiar incandescent lamp, though the best of all methods of illumination, is also the most expensive. Mr. Hewitt's lamp, though not yet adapted to all the purposes served by the Edison lamp, on account of its peculiar color, produces eight times as much light with the same amount of power. It is also practically indestructible, there being no filament to burn out; and it requires no special wiring. By means of this invention electricity, instead of being the most costly means of illumination becomes the cheapest--cheaper even than kerosene. No further explanation than this is necessary to show the enormous importance of this invention." As just stated, the defect of the Edison incandescent lamp is its cost, due to its utilizing only a small fraction of the power used in producing the incandescence, and, of much less importance, the relatively short life of the filament itself. Only about three per cent. of the actual power is utilized by the light, the remaining ninety-seven per cent. being absolutely wasted; and it was this enormous waste of energy that first attracted the attention of Mr. Hewitt, and led him to direct his energies to finding a substitute that would be more economical. A large part of the waste in the Edison bulb is known to be due to the conversion of the energy into useless heat, instead of light, as shown by the heated glass. Mr. Hewitt attempted to produce a light that would use up the power in light alone--to produce a cool light, in short.