Tesla's Vacuum-tube Lighting

As is well known, Mr. Tesla has been engaged on experiments in vacuum-tube lighting for the last decade. According to the daily press, he has recently made a considerable advance in this direction. From one account the following statements are taken:

New York, January 26. — Nikola Tesla, who has been striving for years to produce an electric light without heat, feels that he is making perceptible headway in that undertaking. His general plan is to use an alternating current of almost inconceivably great frequency and a lamp consisting of a vacuum tube. The alternations are secured by an instrument of his own invention, known as the oscillator. But after Mr. Tesla entered upon his interesting line of experimenting he encountered various unforeseen difficulties. While he was able to obtain a beautiful light almost at the outset, it was at the expense of more energy than was desirable. In other words, he did not have his invention on a thoroughly satisfactory basis.

By degrees he has improved the efficiency of his apparatus so that his light is now more economical than it was, and he regards it as superior to both the incandescent and arc, lights in this respect. At present, however, he is. unwilling to indicate precisely the nature and degree of the technical advances made or to use figures in comparing its economy with that of its rivals. One reason for reticence on the latter point may be a recognition of the possibility of further improvement. Mr. Tesla frankly declares that his lamp is not yet perfect. It does not make as good a return in light for the electrical energy invested as he would like. All that he insists upon is that it is now so efficient that he can conscientiously recommend it to those who may wish to put it on the market.

In some of his earlier experiments Mr. Tesla used a straight vacuum tube fully an inch and a half in diameter and six or eight feet long. Latterly, he has employed a more slender one, and by arranging this tube in the shape of a rather compact coil he saves a great deal of space.

A score of lamps of this sort, each with a porcelain reflector over it, may be suspended from the ceilings of rooms on the tenth floor of an office building, while the special apparatus which modifies the current for their use would be down in the basement. The street mains would supply an ordinary alternating current and other wires would lead from the oscillator up to the lamps. For some purposes two wires to each lamp would be preferable, but for others one would suffice. Less copper would be required for inside wiring, and the risks from escaping currents would be diminished rather than increased. The present style of insulation would be more than sufficient.