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INVENTIONS OF NIKOLA TESLA.

to allow reading ordinary print at a distance of five to six paces.It was of interest to see liow some of the phosphorescent bulbsof Professor Crookes would behave with these currents, and hehas had the kindness to lend me a few for the occasion. Theeffects produced are magnificent, especially by the sulphide ofcalcium and sulphide of zinc. With the disruptive dischargecoil they glow intensely merely by holding them in the hand andconnecting the body to the terminal of the coil.

To whatever results investigations of this kind may lead, thechief interest lies, for the present, in the possibilities they offerfor the production of an efficient illuminating device. In nobranch of electric industry is an advance more desired than inthe manufacture of light. Every thinker, when considering thebarbarous methods employed, the deplorable losses incurred inour best systems of light production, must have asked himself,What is likely to be the light of the future ? Is it to be an in-candescent solid, as in the present lamp, or an incandescent gas,or a phosphorescent body, or something like a burner, but in-comparably more efficient?

There is little chance to perfect a gas burner; not, perhaps,because human ingenuity has been bent upon that problem forcenturies without a radical departure having been made—though the argument is not devoid of force—but because in aburner the highest vibrations can never be reached, except bypassing through all the low ones. For how is a flame to proceedunless by a fall of lifted weights ? Such process cannot be main-tained without renewal, and renewal is repeated passing from lowto high vibrations. One way only seems to be open to improvea burner, and that is by trying to reach higher degrees of incan-descence. Higher incandescence is equivalent to a quicker vi-bration : that means more light from the same material, and thatagain, means more economy. In this direction some improve-ments have been made, but the progress is hampered by manylimitations. Discarding, then, the burner, there remains thethree ways first mentioned, which are essentially electrical.

Suppose the light of the immediate future to be a solid, ren-dered incandescent by electricity. Would it not seem that it isbetter to employ a small button than a frail filament ? Frommany considerations it certainly must be concluded that a buttonis capable of a higher economy, assuming, of course, the diffi-culties connected with the operation of such a lamp to be effec-