HIGH FREQUHNVY AND HIGH POTENTIAL (tURRENTS.

121

of lighting an apartment by simply creating in it sncli an electro-static field, and this, in a certain way, would appear to be theideal method of lighting a room, as it would allow the illuminat-ing device to be freely moved about. The power with whichthese exhausted tubes, devoid of any electrodes, light up is cer-tainly remarkable.

That the principle propounded by Mr. Tesla is a broad one isevident from the many ways in which it may be practically ap-plied. We need only refer to the variety of the devices shownor described, all of which are novel in character and will, with-out doubt, lead to further important results at the hands of Mr.Tesla and other investigators. The experiment, for instance, oflighting up a single filament or block of refractory material witha single wire, is in itself sufficient to give Mr. Tesla’s work thestamp of originality, and the numerous other experiments andeffects which may be varied at will, are equally new and interest-ing. Thus, the incandescent filament spinning in an unex-hausted globe, the well-known Crookes experiment on open cir-cuit, and the many others suggested, will not fail to interest thereader. Mr. Tesla has made an exhaustive study of the variousforms of the discharge presented by an induction coil when op-erated with these rapidly alternating currents, starting from thethread-like discharge and passing through various stages to thetrue electric flame.

A point of great importance in the introduction of high ten-sion alternating current which Mr. Tesla brings out is the neces-sity of carefully avoiding all gaseous matter in the high tensionapparatus. He shows that, at least with very rapidly alternatingcurrents of high potential, the discharge may work through al-most any practicable thickness of the best insulators, if air ispresent. In such cases the air included within the apparatus isviolently agitated and by molecular bombardment the parts maybe so greatly heated as to cause a rupture of the insulation.The practical outcome of this is, that, whereas with steady cur-rents, any kind of insulation may be used, with rapidly alternat-ing currents oils will probably be the best to employ, a factwhich has been observed, but not until now satisfactorily ex-plained. The recognition of the above fact is of special impor-tance in the construction of the costly commercial induction coilswhich are often rendered useless in an unaccountable manner.The truth of these views of Mr. Tesla is made evident by the in-