Letter: Tesla On Current Interrupters

Wednesday, March 15, 1899
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March 15, 1899 TESLA ON CURRENT INTER- RUPTERS. To 'ral Enrron or Eu:o'rn.u:AL Rlvilv: I Wish to acknowledge the receipt of your favor of March 11, and thank you for calling my attention to the matter of the “electrolytic current interrupter." Pressing work has for the past few weeks claimed all my time, and 1‘ have been unable='to peruse the technical periodicalsyancl it is only a`few days ago that'I noticed an article descriptive of the'device. Upon receiving your note'I have gone over the journals and have read the articles and comments that have ap- peared. Most of them are indicative of time ill-spent for the purpose of comprehending the requirements of such an apparatus. 'l`o stimulate the nrdor of the zeal- ous axperimeuters, who believe inthe revolutionary cliuructer of this dis- covery,‘it might be well to suggest one or two such simple devices for interrupting the current For in- stance, a very primitive contrivance of this kind eomprisesapoker#yes; an ordinary poker. connected hy means of a flexible cable to one of the mains of the generator, and a bathtub filled' with conducting fluid which is connected in anysuitable manner, through the primary of an induction coil, to the other pole of the generator, When the experi- menter desires tn tuko n Roontgen picture, he brings the end of the poker to white heat, and, thrusting the same into 'the bathtub, he will at once witness an astonishing phe- nomenon, the seething and boiling liquid making and breaking the eur- rent in rapid succession, and the powerfull rays generated will ut once convince him of the great practical value of this discovery. l might further suggest that the poker may be conveniently heated by means of 9. welding machine. Another device, entirely automatic, and probably suitable for use in subs urban districts, comprises two insu- lated metal plates, supported in any convenient manner, in close proximity to each other. These plates are con- nected throngh the primary of an in- duction coil 'with tho terminals of a g0l\0l`||l}0|', iiuil are bridged by two movable contacts joined bya flexible cable. The two contacts are both attached to the legs of a good-sized chicken standing astride on the plates. Heat' being-applied to the latter, muscular contractions ure pro- duced in the legs of the chicken, which thus makes und breaks the current through the induction coil. Any number of such chickens may be ELECTRICAL REVIEW provided and the contacts connected in series or multiple arc, as may be desired, thus increasing the frequency of the illlLlPll1_B6S. In this manner iierce sparks, suitable for most pur- poses, may be obtained, and vacuum tubes may be operated, and these cou- trivauces will be found a notable im- provementyou certain circuit-breakers of old, with- which two enterprising editors undertook some years ago to revolutionize the systems of' electric lighting. The enterprising editors n|'e_ wiser now. They are to, be eon- gratulated, and their readers, scientific societies and the profession, all ought to be congratulated, and-“all is well that ends well.” The observant ex- perimenter will not fail to note that the fierre sparks frighten the chickens, which are thus put into more violent spasms and muscular contractions, this again increasing the ilorcenoss of the sparks, which, in return, causes a greater fright of the chickens and in- creased speed ofdnterruptions; it is, in fact, as Kipling says: “interdependence absolute, foreseen, or- dained, decreed. To work, ye'll note, at'any'tl`lt‘ uh' every rlite o' spccd.” But to return, in all enrnestuess, to the “electrolytic interrupter” de- scribed, this is a device with \vhich I am perfectly familiar, having carried on extensive experiments with the sunie two or three yours ago. lt wus one of many devices which 1 invented in my efforts to produce an econom- ical contrivance of this kind. The name is really not appropriate, inas- much as any fluid, either conducting or made so in any manner, as by being rendered acid or alknline, or by being heated, may be used, I have even found it possible, under certain con- ditions, to operate with mercury. The device is extremely simple, but 'the great waste of energy attendant hpon its operation andcertain other defects make it entirely unsuitable for any valuable, practical purpose, and as far as those instances ure concerned, in which a small amount of energy is needed, much better results are ob- tained by' a properly designed me- chanical circuit-breaker. The ex- perimenters ure very likoly iloceivoil by (hiding ,thut an iuiluctiou coil gives longer sparks when this device is inserted in place of the ordinary break, but this is due merely to the fact that the break is not properly de- signed. Of the total energy supplied from the mains, scarcely one-fourth is obtainable of that amount, which n well constructed mechanical break furnishes' in the secondary, and al- though I have designed many im- proved forms, I have found it impos- sible to increase materially the econ- omy.- Two improvements, however, which I found at that time nec- essary to introduce,_ I_may mention forthe benefit of those who are using the device. As will be readily noted, the smell terminal is surrounded by a gaseous l)lll.)l)l0,l`i'1 \vhich the makes and breaks ure fcriiicil, generally in an irregular manner, by the liquid being driven towards the terminal at some point, Theforce which drivestheliquid is evidently the pressure of the fluid column, and by increasing the iluid pressure in any manner the liquid is forced with greater speed towards the terminal and thus the frequency is increased. Another necessury im- provement wus to make a provision for preventing the acid or alkali from heing carried olf into the atmosphere, which always happens more or less, even if the liquid column be of some height. During my early experi- ments with the device I became so interested in it thatpl neglected this precaution, and I noted that the acid had attacked all the apparatus in my laliorutriry. The :experimenter will conveniently carry out both of 'these improvements by taking a long glass tube of, sny, six to eight feet in length, and arranging the interrupt- ing device close to the bottom of the tube, with an outlet for eventually roplucirigg thu liquiil. 'l‘he high col- umn will prevcut the fumes from vitiating the atmosphere of the room, and the increased pressure \vill add materially to the effectiveness of the performance. If the liquid column be, say, nine times as high, the force driving the lluid towards the contact is nine times as great, and this force is capable, under the same conditions, of driving the fluid three times as last, hence the frequency is in- creased in that ratio and, in fact, in a somewhat greater ratio, as the gaseous bubble, being compressed, is rendered smaller, and therefore the liquid is made to travel through a smaller dis- tuuce. The electrode, of course, should he very small to insure the regularity of operation, and it is not necessary to use platinum. The prusaiiro muy, however, lin iinzrensed in other ways, und I have obtained some results of interest in experi- ments of tl1is kind. As before stated, the device is very wasteful, aud,while it may be used in 167 in which by far better results are ob- tainable with devices equally simple, if not more so. I may mention one here, based on a different principle, which is incomparuhly more eifective, more efficient and also simpler on the whole. It comprises a tine stream; of conducting fluid which is made‘to issue, with any desired speed, from an orifice connected witlpriiie pole of a generator, through the primary ol' the induction eoil, against the other terminal of the generator placed at a small distance. This device gives dis~ charges of a remarkable suddenness, and the frequency may be brought within reasonable limits, almost to anything desired. I have used this device for a long time in connection with ordinary coils and in at form of my own coil with results greatly superior in every respect to those obtainable with the form of device discussed. If time permits I shall, iu compli- ance with the request expressed in your letter, make a few statements re- ferring to such make and break dc- vices in general, and various forms based op this new principle. Yours very truly, N. TESLA. New York, March 13.