Nikola Tesla - Free-Energy Devices

HIGH FREQUENCY AND HIGH POTENTIAL CURRENTS. 241much smaller diameter. To still further reduce the dangerarising from the heating of the glass stem, and also with the viewof preventing an electrical connection between the metal tubeand the electrode, I preferably wrap the stem with several layersof thin mica, which extends at least as far as the metal tube. Insome bulbs I have also used an outside insulating cover.The preceding remarks are only made to aid the experimenterin the first trials, for the difficulties which he encounters he maysoon find means to overcome in his own way.To illustrate the effect of the screen, and the advantage ofusing it, I have here two bulbs of the same size, with their stems,leading-in wires and incandescent lamp filaments tied to the latter,as nearly alike as possible. The stem of one bulb isprovidedwith an aluminum tube, the stem of the other has none. Originallythe two bulbs were joined by a tube which was connectedto a Sprengel pump. When a high vacuum had been reached,first the connecting tube, and then the bulbs, were sealed off ;they are therefore of the same degree of exhaustion. When theyare separately connected to the coil giving a certain potential, thecarbon filament in the bulb provided with the aluminum screenis rendered highly incandescent, while the filament in the otherbulb may, with the same potential, not even come to redness,although in reality the latter bulb takes generally more energythan the former.When they are both connected together to theterminal, the difference is even more apparent, showing the importanceof the screening. The metal tube placed on the stem containingthe leading-in wire performs really two distinct functions: First,it acts more or less as an electrostatic screen, thus economizingthe energy supplied to the bulb ; and, second, to whatever extentitmay fail to act electrostatically, it acts mechanically, preventingthe bombardment, and consequently intense heating andpossible deterioration of the slender support of the refractory incandescentbody, or of the glass stem containing the leading-inwire. I say slender support, for it is evident that in order toconfine the heat more completely to the incandescing body its supportshould be very thin, so as to carry away the smallest possibleamount of heat by conduction. Of all the supports used I havefound an ordinary incandescent lamp filament to be the best,principally because among conductors it can withstand the highestdegree of heat.The effectiveness of the metal tube as an electrostatic screendepend? largely on the degree of exhaustion.