Letters To The Editor: Tesla's New Alternating Motors
industries, ian November. 1890. Jeffers io i£§e Qtéifov. TESLA’S NE\V ALTERNATING MOTORS. To 'nm Enrroa or “IrmlJs'rnns." Sm,-In your issue of the 10th October I find an article relating to some remarks made by me in other journals. You say “it is perhgps an ‘pversiphf " cn my part that I have not forwarded you sn a vaucs proo o m rsmar s. Iadmit the justies ofy this remark, and beg you to accept my apology. But while l do this I must saythat I do not agree with some of your statements. You still misunderstand me on some points about the luot/or which you have made ths subject of your crificigin. Ishit because my explanations and views are “ ecceu ic, or er aps svou unsound In the n\otor Fyou refer to, the four coils are wrap ed trans- versely with the fins iron wire-that is, the axis of tlla wire is parallel with the lines of force or induction set up by the current through the coils. This arrangement was referred to by me as a closed magnetic circuit, and is so for all pracrical purposes. My statement was that on the start, and as long as the current through the coils has a small value, the few lines set up close through the iron wire, and thus the two effects mentioned by me are brought about, namely, the current through the coils is re~ torded, and tha appearance of the free poles delayed. I believe that it is proper to say that, in this ruse, the “screening ” is edected "magnetimlly," since the formation of the secondary currents in the “ screen " is reduced as far as practicable. You scem to overlook that in advancing the views in question I have, as far us my recollection goes, nowhere stated that the “ screening" might not bc flue to Foncault. currents, which are fornicd no matter how finely the core may be subdivided. What- ever was said referred to the fact observed, and not to what may have caused it. If I observe that the outside of a core is mag- netised tlrst, I think that I should be allowed to say in a popular way that thedruagnetio action affects the outside first and pro- gresses towar s t e interior. As to the Foucault currents hsiug concerned in the phenomena, I had, obviously, views similar to your own. _ In exploring the field of a motor by means of a rotating disc, I have several times observed what one might call “ magnetic eddies." In some places within the field the disc would rotate in the proper diwction, in other places-the axis of the disc being always paiallel with the axis o the armaturs of the motor-it would not rotate, or it would even rotate in the iappcsite direction, though with less force in cabo; plieceea of the eld. Yet tlae cores were well laminated, and t e e coi s properl connecte _ I explained this hyyassuming that, ou the start of the current throng the coils, secondary currents are formed throughout the cores. These currents in each core might be re laced by a single current sheet somewhere beneath the surface. The space between this cunent sheet and the surface of the core would then be mag- netised jointly hy the primary and secondary currents, whereas the centre is demaguetised by the secondary. As there is a difference of haaa besides, it occurs sometimes that the centre ac ulrea a pollzrity opposite to that which would be imparted to it rlzy the prima current. The core may than be thought to consist. of two iddependent parts, and these phenomena of rota- tion occur. Motors were constructed by me on this and similartplaus. The only trouble with this view is that 1 have observe these and other phenomena with well-laminated oores. I have, therefore, tried to explain tha phenomena in many other ways more or less in accordance with the facts observed, and I do not agree with you in the opinion that it. is necrsraq/ to aasums the action to be due to Foucanlt currents, I mean currents circulating in paths of measurable length. _ The magnetic loree around a conductor conveying current diminishes with the distance. The msgnetisatiou being an_ ar- rangemeut displacement or orientation of parts possessing weight and inertia requires time. When a sudden magnetlsmg force is applied to the core (by passing s. current through the coil sur- rounding the core) it may occur that the outside-that is; the side nearest to the coil-is magnetiaed tlrst, though the orce ap ears in every part of the oere without loss of time, but ditgerent iu intensity. The magnetisatiou thus spreads towards the portions of the core where the force is less intense. ds the current sinks down to zero and reverses, a wave_of maguetxsation passes from the stronger to the weaker magnetiaed parts, partly on account of the tendency to equaliaatiou throughout the core when the same is maguetised and left to itself, and partly because of the repulsion which is exerted by the current upon the existing polarity. The changing permeability of the parts may also be of more or less influence, Various other explanations, more or less “ eccentric," have suggested themselves to me. You state that I have misinterpreted my results, audit looks as though you believe my views to be unsound. Yourargumeuts are those of an crnineut scholan I was myself a fair scholar. For years l pondered. so to speak, day and night over books, and filled my head with sound views-very sound ones, indeed-those of others. But I could not get to practical results. then began to work and think independently. Gradually my views became unsound, but they conducted ma to some sound results. Yours, tc., Nixon Tnsu. Astor House, New York, U.S.A., 28th October, 1890.