Nikola Tesla - Free-Energy Devices

232 INVENTIONS OF NIKOLA TESLA.side, and close to it, an insulated metal plate.The static screenmay, however, be omitted, and simply a thickness of insulatingmaterial fastened to one of the sides of the fan.To show the behavior of the coil, the fan may be placed uponthe terminal and it will readily rotate when the coil is operatedby currents of very high frequency. With a steady potential,of course, and even with alternating currents of very low frequency,it would not turn, because of the very slow exchange ofair and, consequently, smaller bombardment; but in the lattercase itmight turn if the potential were excessive. With a pinwheel, quite the opposite rule holds good; it rotates best witha steady potential, and the eifort is the smaller the higher thefrequency. Now, it is very easy to adjust the conditions so thatthe potentialisnormally not sufficient to turn the fan, but thatby connecting the other terminal of the coil with an insulatedbody it rises to a much greater value, so as to rotate the fan, andit is likewise possible to stop the rotation by connecting to theterminal a body of different size, thereby diminishing the potential.Instead of using the fan in this experiment, we mayuse the" electric" radiometer with similar effect. But in this case it willbe found that the vanes will rotate only at high exhaustion or atordinary pressures; they will not rotate at moderate pressures,when the air is highly conducting. This curious observation wasmade conjointly by Professor Crcokes and myself. I attributethe result to the high conductivity of the air, the molecules ofwhich then do not act as independent carriers of electric charges,but act all together as a single conducting body. In such case,of course, if there isany repulsion at all of the molecules fromthe vanes, it must be very small. It is possible, however, thatthe result is in part due to the fact that the greater part of thedischarge passes from the leading-in wire through the highly conductinggas, instead of passing off from the conducting vanes.In trying the preceding experiment with the electric radiometerthe potential should not exceed a certain limit, as then the electrostaticattraction between the vanes and the glass of the bulbmay be so great as to stop the rotation.A most curious feature of alternate currents of high frequenciesand potentials is that they enable us to perform many experimentsby the use of one wire only. In many respects this feat,ure is of great interest.