"I had an equation with a large number of unknown quantities," he said. "About the only thing known for a certainty was the amount of current passing into the receptacle containing the gas, and its pressure. I had to assume values for these unknown quantities in every experiment, and you can understand what a great number of trials were necessary, using different combinations, before obtaining results. I presume thousands of experiments were made." Many other investigators had been on the very edge of the discovery. They had tried sending strong currents through a vacuum tube containing mercury vapour, but had found it impossible to control the resistance. One day, however, in running a current into the tube Mr. Hewitt suddenly recognised certain flashes; a curious phenomenon. Always it is the unexpected thing, the thing unaccounted for, that the mind of the inventor leaps upon. For there, perhaps, is the key he is seeking. Mr. Hewitt continued his experiments and found that the mercury vapour was conducting. He next discovered that _when once the high resistance of the cold mercury was overcome, a very much less powerful current found ready passage and produced a very brilliant light: the glow of the mercury vapour_. This, Mr. Hewitt says, was the crucial point, the genesis of his three inventions, for all of them are applications of the mercury arc. Thus, in short, he invented the new lamp. By the use of what is known to electricians as a "boosting coil," supplying for an instant a very powerful current, the initial resistance of the cold mercury in the tube is overcome, and then, the booster being automatically shut off, the current ordinarily used in incandescent lighting produces an illumination eight times as intense as the Edison bulb of the same candle-power. The mechanism is exceedingly simple and cheap; a button turns the light on or off; the remaining apparatus is not more complex than that of the ordinary incandescent light. The Hewitt lamp is best used in the form of a long horizontal tube suspended overhead in a room, the illumination filling all the space below with a radiance much like daylight, not glaring and sharp as with the Edison bulb. Mr. Hewitt has a large room hung with green material and thus illuminated, giving the visitor a very strange impression of a redless world. After a few moments spent here a glance out of the window shows a curiously red landscape, and red buildings, a red Madison Square, the red coming out more prominently by contrast with the blue-green of the light. "For many purposes," said Mr. Hewitt, "the light in its present form is already easily adaptable. For shopwork, draughting, reading, and other work, where the eye is called on for continued strain, the absence of red is an advantage, for I have found light without the red much less tiring to the eye. I use it in my own laboratories, and my men prefer it to ordinary daylight."