Experiments With Alternating Currents Of High Frequency

Friday, June 5, 1891
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EXPERIMENTS WITH ALTERNATING CURRENTS OF HIGH FREQUENCY! T1-In recent meeting of tho Anicricnn Institute of Electrical Engineers will long be remembered by those present, not only on nceount ol the brilliant exiieriments shown in connection Withvn. lecture given by Mr, Niko n Tesla., hut also for the many Possi- bilities which it suggested in the development of the srtliicial illumination of the future. For the purpose of his experiments, Mr. Tesla employed sn alternating nntchine with 400 poles, which, when run at full srieed, permitted him to obtain 20,000 alternntions per second. ‘he currents of this machine in all of Mr. Teslfs experiments were ilrst ruu through n. oondensor in order to avoid the possibility of injury in the machine. The ma.- chine itself was set up in the electrical wnrkshe of the colle e, and was driven by unslectric motor, the speed oiiwhich could the varied by A switch on the lecture platform, Mr. Tesla introduced his subject by the remark that modern science hes been able to make rapid strides by the recognition oi other ls the medium of transmission of vibrations of various forms which manifest themselves to our senses. We are there- fore able now to see things in s, diierent light then was formerly the case, and being tolerably well able to explain them, the truth cannot be hidden much longer. The answer to the question, “ What is Electricity? ” we were not yet prepared to give, We were justined in assuming, however, that electric phenomena. are ether phenomena, and we may consider the phenomena of statin electricity ss phenomena of ether under strain, and those of dy- namic electricity and electromngnetism ss phenomena. of other in motion, The lecturer, while expressing the highest consideration for the work ol Dr. Lodge, wus not in entire accord with the views advanced by him, which he considered to be more of the nature of ingenious exglsnntions then of s probable theory, the lecturer contending t et there can be no two electricities. Alluding further to the electromagnetic theory of light, and to the Hertz experiments md those o Dr. Lodge. and their application to the production of an eilieient source o light, the lecturer considered the electromagnetic waves as unavailable for the production of luminous eifects, for the reason that long before we could reach the newsssry frequency the conductor would become opaque to the passage of the wnves. The lecturer thought that electro- magnetic weves, unless they have the frequency of true light waves, cannot produce luminous oiiscts. Not so, however, with the electrostatic Waves or thrusts. These, no matter what their Irequency, can excite luminous rndiutinnl He reasoned thet the static effects in the Hertz and Lodge experiments were excessively snmll, due to the fact that they were produced in a practically closed coil, the spsrlr acting sts s. bridge, makin the coil practically continuous and depressing the potential. Tooitsjn the desired diiierence of potential we must work with un open circuit gensrntor of high potential of high frequency to enhance the electrostatic eiects, and it wns the recognition of this fact which led the lecturer to the results he showed. ln carrying out this idea. of obtaining enormous differences of potcntinl, the lecturer st once encountered the diiliculty of ob- taining the requisite insulation for the induction wil em loyed by him. His experience demonstrated that what we consigerthe best insulators, sueh as glass and rubber, sre inferior to others, nut former? so considered, such as oil and wex. The lecturer then stsrte n spark coil in action, the primary ol which was in connection with his alternator which was speeded to give from 10,000 to 11,000 nlternltions per second. The coil emitted sclear note, which rose As the number of sltemations was increased. As " Ahsinct of I recent 'paper reed b M . Nik ll T IA bel' th Amerinu lnltituti of Electricnl Erlgillwrzi got tb; shoe; lhltitgl wi: ue indebted to mir Amnicm eontamporlry the Elem-i¢-n,l Engine: r. £'§1151¢Sf1fi¢S, 5th June, 1891. the discharges took pluce helween the terminals of the coil, nn exhausted Geissler tube held in roxiniity to the discharge did not light, but upon blowing out the src the tube lighted up, which was due to the rise of potential caused by the rupture of the urn. This effect tho lecturer considered ss purely electrostatic. Mr. Tesla then showed the iniluence of insulated bodies lmving considerrthle size upon the spark length demonstrating the eiicct of capacity upon the nature of the discharge. Thus, when wo attach sninsulnted body to the terminal of the coil, the potential maybe raised or lowered, He showed this hy wrapping an insulated wire of About one foot in length about one terminal of the coil, and touehin the other tenniusl with is. brass sphere held in the hand; ungsr these conditions streams of light eniansted from all sides of the wire. When the sphere was removed, however, the streams disappeared almost eu- tirely. He then cut oif the wire in successive lengths, and the stream discharges became more marked and brilliant. He then attached it fins platinum wire to the terminal, which also showed the streams to n. remarkable degree, and kept up s continuous vibration to and fro, He also showed n pin- wheel elfoot, the wheel being rapidly rotated with streams issuing from the two points. Another experiment consisted in attaching two spheres of about 4iu. diameter to the ter- minals. The spnrk passes first between the t\vo points nearest to each other _on the s heres, then works up toward their tops, is extinguished ami) is re-established at the iirst point, this bcing continuously re ated. The neighbouring exhausted tubes end lamps were ilgiimineted and extinguished in unison with the action of the spsrk between the spheres. These, the lecturer pointed cut, were not electromrtgnetic vibra- tions like tho Hertz waves, He showed how by the use of the dielectric the spark is induced to jump botween the sepsrsted syhores due to the increase in the speciic inductive capacity o the medium, and he also demonstrated that the stream- ing discharge assed easily through thick lass plates, rubber plates, and s hook. The lecturer then siiowed these static effects in n non~strikiug vacuum. A tubc of this nature when connected to the rneohine glowed brightly, and the tem\inals became incandescent. The lecturer renmrkcd thnt if, instead of using s filament in A nmp_wmc1\ necessarily limited us in the degree of incundescenoe which we could practically employAwe could employ solid blocks of carbon, much higher uiliciency could be obtained. Based upon this reasoning, he has constructed ii lump which ho showed, containing two blocks of catrlvon in non~striking vacuum. When connecting these two oerbons to the two terminals oi the coil or one to one terminal and the other to e body of some size, the blocks can be raised to high iucendoscenee. (To be continued.)