Experiments With Alternate Currents Of Very High Frequency And Their Application To Methods Of Artificial Illumination

Wednesday, May 20, 1891
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JUL! 24, 189I.] EXPERIMENTS WITH ALTERNATE OUR-' RENTS OF VERY HIGH FREQUENCY AND THEIR APPLICATION TO. METHODS OF ARTIFICIAL ILLUNHNATIONJ BY NIKOLA TESLA. Tasse is no subject mom captivating, more worthy oi study, than nature. To nnderstaud~this great nxechanism, to discover the forces which are alrftive, and the laws whiglpgpuern them, is the highest nini of the inte ect of man, ' Nature has stored up in the universe inlinite energy. 'l‘hc etenml recipientnnd tnnsxnittcr of this infinite energy is the ether. The x‘eeognitiun*of'.'the existence of ether, and Q! the functions it performs, iscne of ‘theemost important results of modern scientific research.- The mate abandoning of the idea of action at 1 distance, the sssnmp-. tion of ti medium_pervadj|;5 all space and connecting all gross mutter, has heed-the mindslat-'t nkers of an everpmsent doubt, und, by opening a new horiwn#new and unforeseen possibilities-hns iven fresh interest to phenomena- with which we are familiar of obs It has been A grelt step towards the understanding of the forces ol nature and their rnultifold manifestations to our senses. It hns been for theenlightened student of physics what the understanding of the mechanism of the firearm or of the steam engine was for the hur- barinn. Phenomena upon which we used to look ns wonders bniiling explanation, we now see in a dilferent light, 'l‘he spnrk of nn induc-, tion coil, the glow of an incandescent lamp, the mmiifestaitions of the pxgchanical forces of currents and magnets are no longer beyond Eur grasp finswad of the incomprehensible, u ncfore| their observa- tion suggests how in our mi|isuch'thidg, and excess and want of that one thing, P‘l5sibly; but more probably its condition determines the positive and negative character. , The old theory of Franklin, though falling short in some respects, is, from a certain point of view, after all, the most plausible one. Still, in spite of this, the theory of the two elcctricities is generally acczipte ,as it apparently explains electric henumens in n more 'sati nctory manner. But n theory which iicttcr explains the facts is not necessarily true. Ingenidns minds will invent theories to suit observation, and almost every independent thinker has his own views on the subject. It is not with the object of advancing an opinion, but with the desire of ncquainting you better with some of the results, which I will describe, to sliow you the reasoning I have followed, the departures I have umdefthut I venture to express in s few words the views and convictions which have led me to these results, I adhere tu the idea that there is n thing which we have been in the habit of culling electricity. 'l‘he question is, Whnt is that thing ? _or What, of all things, the existence of which we know, have we the best reason to call electricity 7 We know that it acts like an income pressiblq lluid; that there must be n constant quantity nf it in nature; that it cnn be neither produced nor rleétroyedyund, what is more important, the electro-magnetic theory of light and' all facts observed teach us that electric und ether phenomena are identical. The idea nt once suggests itself, therefore, that electricity might be called ether. In fact, this view has in a certain sense been advancedfhy Dr. Lodge. His interesting work has been read by everyone, and mnny have been convinced by his arguments, His great ability and thc interesting nature of the subject keep the reader spcllbound; but when the impressions inde, one renliscs that he has to denl only with ingenious explnnntiuns. I must confess thut I cannot believe in two electriuities, lunch less in n doubly-constituted ether. The puzzling behaviour of the ether ns nsolid tu waves of light and heat, and ns n lluid to thc :notion of bodies through it, is certainly explained in the most nutur-ul and satisfactory nmnuer by nssumiug it to be in motion, us Sir Willizun 'l‘hon\son has suggested; but regardless of this, there is nothing which would enable ns to conclude with certainty thnt, while n lhiid is not capable of trnnsmittingtransverse vibrations of u few hundred or thousnnil per second, it might not he capable of truusinittiug such vihrutious when they rnnge into hundreds of million millions per second. Nor cnu uuyouo prove that there are tmnsverse ether wnves emitted from nu alternate current machine, giving n small number of nlternntions per second; to such slow dis- turbances, thc ether, if nt rest, nmy behave ns ax true i|uid._ ltcturning to the subject, und bearing in mind that the existence of t\\'o electrlcities is, to say the lenst, highly iuxprobnble, we must re- member that we have nulevidence of electricity, nor cnn we hope to get it, unless gross matter is present. Eleet'riciiGy. therefore, cannot he called ether in the brand sense of the terui; but nothing would seein to stnnd in the way of culling electricity other associated with matter, or bound ether; ur, in other words, that the su-called static

'IBB TEKJGBAPHIO- JOURNAL AID 104 ELECTRICAL REVIEW. fm" 24' "9" charge of the molecule is ether associated in some way with the mole- First will be met the ditlieulty of obtaining the required fre- cule. Looking at it in that light, we would be justified in saying that electricity is concerned in all molecular actions. Now, precisely what the ether surrounding the molecules is, wherein it differs from ether in general, can only be ponjeotured. It cannot differ in density, ether being incompressible ; it must, there- fore, be under some strain or in motion, and the latter is most pro- bable. To understand its functions, it would be necessary to have an exact idea of the physical construction of matter, of which, of course, we c:\n only form s mental picture. But of all the views on nature, the one which assumes one matter and one force, and a perfect uniformity throughout, is the most scientific and most likely to be true. An infinitesimal world, with the molecules and their atoms spinning and movingin orbits, in much the sarne manner as celestial bodies, carrying with them, and probably spinning with them, ether, or, in other words, carrying with them static charges, seems to my mind the most probable view, and one which, in a plausible manner, accounts for most of the phenomena observed. The spinning of the molecules and their ether sets up ether tensions or electrostatic strains ; the eqmilisstion of ether ten- sions sets up ether motions or electric currents, and the orbital move- ments produced the effects of electro and permanent magnetism. About 15 years ago, Prof. Rowland dcmonstratedamost interesting and important fact, namely, that a static charge carried around produces the effects of nn electric current. Leaving out of considera- tion the precise nature of the mechanism, which produces the attrac- tion and repulsion of currents, and conceiving the electrostaticslly charged mo ecules in motion, this experimental fact gives us a fair idea of magnetism. We can conceive lines or tubes of force which physically exist being formed of rows of directed moving molecules; we can see that these lines must be closed: that they must tend to shorten and expand, rtc. It likewise explains in a reasonable way the most puzzling phenomenon of all, permanent magnetism, and, in general, has all the beauties of the Ampére theory without possessing the vital defect of the same, namely, the assumption of molecular currents. Without enlarging further upon the subject, I would say that I look upon all electrostatic current and magnetic phenomena as being due to electrostatic molecular forces. The preceding remarks I have deemed necessary to l full under- standing of the subject as it presents itself to my mind. Of all these phenomena the most important to study are the cur- rent phenomena, on account of the already extensive and ever-grow- ing use of currents for industrial purposes. It is now a cent since the first practical source of current has been produced, ala ever since, the phenomena which accompany the flow of currents have been diligently studied, and through the untiring efforts of scientific men, the simple laws which govern them have been discovered. But these laws were found to hold good only when the currents are of a steady character. When the currents are ra idly varying in strength, quite different phenomena, often unexpected? present themselves, and quite different laws hold good, which even now have not been de- termined as fully as is desimblc,though through the work, principally of English scientists, enough knowledge has been gained on the sub- jcet to enable us to treat simple cases which now present themselves in daily practice. The phenomena which are peculiar tothe changing character of the currents are greatly exalted when the rate of change is increased, hence tl\c study of these currents is considerably facilitated by the employment of properly constructed apparatus. It was with this and other objects in view that I constructed alternate current machines capable of giving more than two million reversals of current per minute, and to this circumstance it is principally due that I am able to bring to your attention some of the results thus far reached, which I hope will prove to be a step in advance on account of their direct bearing upon one of the most important problems, namely, the pro- duction of a practical and ctlicicnt sourec of light. The study of such rapidly :iltemating currents is very interesting. Nearly every experiment discloses something new. Many results may, of course, he predicted, but many more are unforeseen. The experimenter makes many interesting observations. For instanec, we takeapiecc of iron and hold it against a magnet. Starting from low altcrnntions, and running up higher and higher, we feel the im- pulses succeed ench other faster and faster, get weaker and weaker, and Gnally disappear. We then observe n continuous pull; thc pull, of course, is not continuous; it only appears so to us; our sense of touch is imperfect. We may next ustahlish :tn arc between the electrodes and uhscrve as thc altcrnzitions rise, that thc note which nccompnnics alternating arcs gets shrillcr and shriller, gradually weakens, and linnlly ceases. The uir vibmtions, of course,continue, but they arctoo weak to be pcr- ceived ; our sense of hearing fails us. We observe the small physiological effects, the rapid heating of the iron cores and conductors, curious inductive effects, interesting coin denser phenomena, and still more interesting light phenomena with a high tension induction coil. All these experiments and observa- tions would be of the greatest interest to the student, but their de~ scription would lead mo too for from the principal subject. Partly for this reason, and partly on account of the vastly greater import- ance, I will confine myself to the description of the light effects produced by these currents. In the experiments to this cud n high tension induction coil or equivalent apparatus for converting currents of comparatively low into currents of high tension is used. If you will he suilicicntly interested in the results T shall describe as to enter into nn experimental stud; of this subject; if you will he convinced ofthe truth of the arguments l shall sdvsiwe, your niwn will be to produce high frequencies and high potentials; in other words, powerful elcct1'ost:\ti<: cl\`ccts. You will then encounter many diliicultics, which, if complet/ely overcome, would allo\v us to produce truly wonderful results. quencies by means of mechanical apparatus, and, if they be obtained otherwise, obstacles of a different nature will present themselves. Next it will be found dimcnlt to‘provide the requisite insulation without considerably increasing the size of the qplpamtus, for the potentials required are high, an , owing to the rapi 'ty of the alter- nations, the insulation presents peculiar didiculties. So, for instance, when a gas is present, the discharge may work, bythe molecular bombardment of the gas and consequent heating, through as much as an inch of the best solid insulating material, such as glass, hard rubber, porcelain, sealing wax, &c. ; in fact, through any known insu- lating substance. The chief requisite in the insulation of the appaf mtus is, therefore, the exclusion of any gaseous matter. In general my experience tends to show that bodiei which possess the highest specific inductive capacity, such as glass, afford a rather inferior insulation to others, which, while they are goodinsulators, have a much smaller specific inductive capacity, such‘ as oils, for in- st1mee,thc dielectric losses being no doubt greater in the former. The ditliculty of insulating, of course, only exists when the potentials are excessively high, for with potentials such as a few tiousand volts there is no particular difficulty encountered in conveying currents from a machine giving, say 20,000 alternations per second, to quite a distnnce. This number of alternations, however, is by far too small for many purposes, though quite sudicient for some practical appli- cations. This didiculty of insulating is fortunately not a vital draw- back ; it affects mostly the size of the apparatus,for, when excessively high potentials would be used, the light-giving devices would he located not far from the apparatus, and often they would be quite closeto it. As the air bombardment of the insulated wire is de- pendent on condenser action, the loss may be reduced to a tritlc by using excessively thin wires heavily insulated. Another difficulty will be encountered in the capacity and self- induction necessarily possessed by the coil. If the coil be large, that is, if it contain a glreat length of lire, it will be generally unsuited for excessively hig frequencies; lf it be small, it may be well ada ted for such frequencies, but the potential might then not be as higlgas desired. A good insulator, and preferably one ‘possessing a small specific inductive capacity, would aiiord a two~fol advantage. First, it would enable us to construct a very small coil ca£able of withstanding enormous differences of potential; and secon y, such a small coil, by reason of its smaller capacity and self-induction, would be capable of a quicker and more vigorous vibration. The roblem, then, of constructing a coil or induction apparatus of any Eind possessing the requisite qualities I regard asone of no small importance, and it has occupied me for a considerable time. _ The investigator who desires to repeat the experiments which I will describe, with an altemate current machine, capable of supplying currents of the desired frequency, and an induction coil, will o well to take the primary coil out and mount the secondary in such a manner ns to be able to look through the tube upon which the secondary is wound. He will then be able to observe the streams which pass from thc primary to the insulating tube, and from their intensity he will know how far he can strain the coil. Without this precaution he is sure to injure the insulation. This arrangement permits, however, an easy exchange of the primaries, which is de- sirable in these experiments. The selection of the type of machine best suited for the purpose must be left to the judgment of the experimenter. ` There are here illustrated three distinct types of machines, which, besides others, I have used in my experiments. _ -- Fig. I represents the machine used in *my experiments before ithxs Institute. The field magnet consists of s ringfof wrought iron with ‘ 1 \ 1 <1 .i a Q F_ \ ~'v’\;‘ ‘ . vi ‘i '//, s \\‘Wl ‘l ll\‘=“ii‘3\‘“1Ill\`i,,;‘,‘u~‘~~‘~.~ 2 - Q?Fill;l~l=\l§l»‘ill#ll:l‘~,: ,miliI1,il-\,1\;\=l1\‘1v\\\*ll§1W' $`,'\,u \> >\`1,`\` Q, ‘,,,“,‘l ~`;`,,3l,,l§,,' 1 s,==:,~; ~¢‘f.~, Wi,,w;‘;\~;\1~' 'ia $“\I:‘1‘=~,i. -. *_ “ , ‘f ‘ fill""fli!slf§."l`l`= ~, \=§r'2,‘ ‘ = .rw "1 U §twisisWM;-l.-1,~~._;/ 1 , E ‘ _»11l~1,\3\=`I3,,1`1‘, Lv ,_ ` f . _. ~ - 2lilllllulllilif fe Elllwi,l;.,;ll.,`§~g1,_ N - l 2llLl;‘,1\l‘\‘,l\=v ,,,;1:l,\l`l\l;ll,p~`,‘11lil;,:~‘§w %‘\:hl~~l~ illwl111~=,\‘,~l\‘~ :M \ s /L J \\~\"Wl“\l\‘lhhi\l,l‘~,~.‘1=‘\`X ` / Ml Wu, , l \\\\\ / "df/,,L;‘\“‘t ‘l ,r \ , / ||||lUllllll\\\ P / Y T* , ll . fl \ Ti l/ ii? -.~.~;=-nfl, 5' 'Nl 4 T;- - - ~ " f __ »- -- Fro.1.-Hrou Fnncvrsncr Anrnnnsron wrrn Dann Aausrvns. 38l pole projcCLio\»s_ 'l`hc armaturc comprises a steel disc to which is fztslcncd a thin, \~:\rc[ully wcldcrl rim of \\'|1\\1ght iron. Upon thi' rim :uv woiind scvcml layers I-f tiue, well-annealed iron wire, which when \vound is passed through shcllac. 'I`he srmaturc wires are wnnml nmnml hmss pins, wrapped with silk thread. The diameter if ll... znmatniu wire in this tyre cf mschine|should not he more than

'Ill Tl!-IGBAPBIU FOUBNAL AND JULY 2% 18914 ELECTRICAL REVIEW. 105 one-sixth ofthe thickness of the pole projections, else the local action will he considerable. Fig. 2 represents s larger machine of u ditfereut type. The Held magnet of this machine consists of two like parts which either enclose an exciting coil, or else are independently wound. Each part has 480 pole projections, the projections of one facing those of the other. The armatnre consists of a wheel of hard bronze, carrying the con- ductors which revolve between the projections of the Held magnet. un ul;12113Wiiiili’,ii~`“g;wv:§»r»i I _ . ,F i f'f*f "~.' l1%lz»1;Mlil¢.> ~'“' A ~ltuncc of the coil. lu thc lluming discharge the E-'lui etfect of the capacity is not perceptible ; the rate nt which the energy is being stored then just equals the nite at which it can be disposed of through the circuit. This kind of discharge is the scverest test for n coil; the break, when itovcurs, is of the nature oi that in nn overcharged Leyden jar. To give n rough approximation, 1 would state that, with an ordinary coil of, say 10,000 olnus resistance, the most powerful ure would be produced with about 12,000 Alternstions per second, When the frequency is increased beyond that rate, the potentinl,of course, rises, but the striking distance nmy, nevertheless, diminish, paradoxical as it muy seem. As the potential rises the coil attains more sud more the properties of n static machine, until, tinnlly, one muy observe the beautiful phenomenon of the streaming discharge, fig. 6, which muy be iroduced aeruss the whole length of the coil. At that stage streunis liegin to issue freely from all points and pro- jections. These strcnms will also be seen to pass in abundance in the space between the primary nnd the insulating tube. When the potential is excessively high they will nlways appear, even ii the frequency be low, and even if the primary he surrounded by as much ss nu inch of wax, hard rubber, glass, or any other insulating sub- stance, This limits greatly the output of the coil, but I will inter show how I have been nhle to overcome to a considerable extent this disadvantage in the ordinary coil. Besides the potcnliail, the intensity of the streams depends on the frequency; but if thc coil be very large they shew themselves, no mutter how low the frequencies used, For instance, in a very large 1-ml of it n-si>lunec of 67,000 nhnis, cumtrnvlcd by mv some time age, tln-_\ sippear uith ns l~-w :is Ili() al\urn=|li yu-| sew-nd and less, thc insulation of the ~--eundziry being ,’ inch of el-onite. When very intvnsc they prodlu-mr ai noise similar to that produ-'ed by the elnnging of an lloltz miuzliinc, but mncli more pmverfnl, and they emit ix strung smell uf ozone. The lower the frequency, the more apt they are to suddenly injure the coil, With excessively high frequencies they

'mn ualsnrmo rounsar. arm ' 106 ELECTRICAL nuvrsw. UU” 24' "9" may pass freely without producing any other effect than to heat the insulation slowly and uniformly. The existence of these streams shows the importance .oi construct- ing an expensive coil so as -to permit of 0ne‘s seeing through the tube surrounding the primary, and the latter should' bs easily exchange- able; or else the space between the primary and secondary should be completely tilled up with insulating material so as to exclude all air. The non-observance of this simple rule in thc construction of the commercial coils isresponsihls for the destruction of many an ex- pensive coil. _ , ' At the stage when the streaming discharge occurs, or-with some- what higher frequencies, one 'may, by ,approaching thelermlnals considerably and regulating properly the ellectvef capacity, roduce averitnblospmy of small silver-white snrlmstor n bunch ol) exces- sircly thin silvery threads (fig. 7) nmid!;t`|\ ‘powerful hrush-each spark or thrcnd possibly corresponding to one alternation. This, when produced under proper conditions, is probably the most beau- tiful discharge, and when an air blast is directed against it,Ht presents a singular appearance. The spray of sparks, when received through thc hody, causes some inconvenience, whereas, when thdedischarge simply streams, nothing nt all is likely to be felt if largelbnducting <_;bjects are held in the hands to protect them from receiving small urns. If the frequency is still more increased, then the c6i~l refuses to give any spark unless at comparatively small distances; and the Efth typical form of discharge may be observed (lig. 8). The tendency to stream out and dissipate is then so great that when the brush is produced nt one terminal no sparking occurs, even if, ,as I have rc' peaterlly tried, the hand, or any conducting object, is held within the stream; and, what is more singular, the luminous stream is not nt all easily deilectcd hy the approach o£`a conducting body. At this stage the streams seemingly pass with the greatest freedom through considerable thicknesses of insulators, and it is particularly interesting to study their behaviour. For this purpose it isconvenient to connect to thc terminals of the coil two metallic spheres which may be placed at any desired distance (fig. 9). Spheres are pre- fcrahle to plates, as the discharge can bc better observed. By insert- ing dielcctric bodies between the spheres, beautiful ‘discharge phenomena may be observed. If the spheres be quite close and a spark be playing between them, by inte osing a thin late of ebonite between the spheres the spark instunltljy ceases andp the discharge spreads into un intensely lnrninous circle several inches in diameter, provided the spheres ure sulticiently large. The passage of 2 the strrxims heats, and, after a while, softens the rubber so much that two plates may be mnde to stick together in this manner. lf the spheres are so fur apart that no spark occurs, even if they are fnr beyond the striking distance, by inserting a thick plate of glass the discharge is instantly induced to pnss from the spheres to the glass in the form of luminous streams. It nppenrs almost ns though these streams pass lhrouyh thc dielectric. In reality this is not the case, as thc stronms nrc due to the molecules of the air which are violently agitated in the space between the oppositcly charged surfaces of the spheres. When no dielectric other than air is present, tl\e hombnrdment goes ou, but is too weak to he visible; hy inserting a dielectric the inductive eilcct is much increased, nnd besides, the projected air molecules lind an obstacle, and the bombardment becomes so intense that the streams become luminous. If by any mecha- niml means we could etiect such a violent agitation of the molecules we could produce the same phenomenon. _ A jct_ of air csca ing through a small hole under enormous pressure and striging against an insulating substance, such as glass, may he luminous in the dark, and it might be possible to produce phosphorescence of the glass or other insulators in this manner. The greater the specilie inductive capacity of the interposed dielec- tric, the more poweriul the eitect produced. 'Owing to ‘this, the streams sho\v themselves with excessively high potentials even if the glass be as much ns li to 2 inches thick. But besides the heating due to bombardment, some heating ocs on undoubtedly in the dielectric, being apparently greater in gloss than in ebonite. I attribute this to the greater specilic inductive capacity of the glass, in consequence of which, with the same potential dilTerence,a greater nmount of energy is taken up in it than in rubber. It is like connect ing to a battery a copper and u brass wire of the same dimensions. The copper wire, though :\ more perfect conductor, would heat more by reason of its taking more current. Thus what is otherwise con- sidered a virtue of the glass is here a defect. Glass usually gives wny much quicker than ebouite ; when it is heated to a certain degree, the discharge suddenly breaks through at one point, assuming then the ordinary form of an are. The heating etieot produced by molecular bombardment of the dielectric would, of course, diminish as the pressure of the air is in- creased, and at enormous pressures it would be negligible, unless the frequency would increase correspondingly. ‘ ` It will be often observed in these experiments that when the spheres are beyond the striking distance, the approach of a glass p ste, for instance, may induce the spark to jump between the spheres. This occurs when the capacity of the spheres is somewhat below the critical value which gives the greatest ditference of poten- tial nt the terminals of the coil. By approaching a dielectric, the specific inductive capacity of the sp:\ce'between the spheres is in- creased, producing the same cileet as if the capacity of the spheres were increased. The potential at the terminals may then rise sohigh that the air space is macked. i The experiment is best performed with dense glass or mimi: ` ; . Another interesting ohservat-ion_ is that a plate of insulating material, when the discharge is passing through it, is strongly attracted by eithenof .thc spheres, that is, by the nearer one, this being obviously due 'to the smaller mechanical ettcct of the bom- bar;_lrnent_ on that side, and/ perhaps .also toF‘the greater felootri- ticu ion. From the behaviour of the dielectrics in these experiments we may conclude, that the best insulator for these rapidly alternating currents would be the one possessing the smallest speeilic inductive capacity and at the same time one capable of withstanding the greatest diiferedces of potential; and thus two diametrically opposite ways of -securing 'the' required insulation are indicated, name y,'t!: usserther alperfect vacuum or ia gas under great pressure \ll’t‘lt\I former would be preferable. Unfortunately neit er of the|¢¢\tilo`¢ways rs easily carried out in practice. _ _ It is especially interesting to note the behaviour of an erdessxvely high vacuum in these experiments. If a test tube, provided wrt external electrodes and exhausted to the highest possible degree, be connected to the lermjnuls of the coil, fig. 10, the electrodes of the tube are instantly brought to a high temperature and the glass at each end of ,the ,ti'il>e,'is réhilered intensely phosphoreseent, hut the middle appcalsvcomparatively dark; and for Ia while remains cool. When thlwlrequency, is so high that the discharge shown in iig._8 is obserye.§fl:onsideralrls dissipation no doubt- occurs in the coil. Nevertheless the coil may be worked for a long time, as the heating IB \l ' fllnM1p‘l&~.o!, the fnctgtrhatfflie dihereucs of potential may be enormous, little is felt when' the discharge _ls passed through the body, provided the hands are armed. This is to some extent due to the higher frequency, but principally to the fact that less energy is available externally, when the, ditfercnoe of potential reaches an enormous value, owin to the circumstancethat, with the rise of potential, the energy agsorbed in the coil increases as the square of the potential. Up to u certain point’the energy available externally increases with the rise of potential, then' it begins to fall of rapidly. Thus, withthe ordinary hrgh tension induction coil, the-curious paraf dox exists, that, while with a given current through the primary the shock might he fatal, with many times that current i rnight_he erfectly harmless, eren if the ircquenoy be the same. _ with high llrequencies and excessively high potentials when the terminals arc not connected td`bodies of some sioerprsetioally all the energy supplied to the primary is taken up by the coil. There 1s no breaking through, no_loca1 injury, but all the material, insulating and conduct- ing, is uniformly heated. _ _ To avoid misunderstanding in regard to the physrologwal effect of alternating currents of very high frequency, 1 think it necessary to state that, while it is un undeniable fact that they are rncomparably less dangerous than currents of low frequencies, yet it shouldnot thought that they are altogether harmless. What has _Just been said refers only to currents from an ordinary high tension 1|1¢i\10¢1°l1 wil. which currents are necessarily very small ; i received directly from a machine or from a secondary of low resistance, they produce more or less powerful eflcct/s, and may cause serious injury, especially when used in conjunction with condensers. _ ' ' _ _ _ The streaming discharge of n high tension rnduetroncorl dillers in many respects from that of a powerful static machine. In colour rt has neither the violet of the positive, nor the brightness of the nega- tive, static discharge, but lies somewhere between, herng_ of _course, alternatively positive and negative. But since the streaming is more powerful when the point or terminal is electrrded positively, than when electrified negatively, it follows that the point of the brush_rs more like the positive, and the root more like the negative static drs~ charge. In the dark, when the brush is very powerful the root may uppmr almost white. The windfproduced by the escaping streams, thou h it may be very strong-o ten indeed to such a degree _that xt rnayie felt quite a distance from the coil-is, nevertheless, considering the quantity of the discharge, smaller than that produced hy the posr- tive brush of a static macliiiiefand it aEeets the Home much less powerfull . From the nature of the phenomenon we can conclude that the higher the Loequeniiy5 the smaller must, of_ eourse, be the wind produced by the streams, and_with suEcierrtly high frequencies no wind at all would _be produced at the ordinary atmospheric pres- sures. With ireq\@neies ohtaihahle by* nieand of a machine, the mechanical el¥e¢$‘is suiliciently great to rcyolve, with considerable speed, large pin-wheels,” which in the dark present a beautiful ap~ pearance owing tothe abundance of the streams (lig. 11). _ In general, most of the ex eriments usually performed with a static machine can be performed with an induction coilwhen operated with very rapidly alternating currents. The eieots _produeed» howeve\§.ixre.much more' striking, beingfof nncompanibly: greater power. f§‘V_hen_a smalllength of ordinary cotton coveredvwrre, Hg. 12, is-attached to- one terminal of the coil, the strea1h§ all pdints of the wire may be so~intense asitoiptoductia 1§0Pl1d0U1bl€ ight effect. When the potentialaand trequene\es~oresyel'y-hfgb, H wire insulated with gutta-percha or rubber and_at6achcd to one of the terminals, appears to be covered with a lumroousffilm. A very thin bare wire w en attached to a terminal emits powerful streams and vibrates continually to and* fro or spins in a circle, producing a singular elfeet (fig. 13). _ Another peculiarity of the rapidly alternating discharge of the induction coil is its radical1y_ diEerent behaviour with respect to points and rounded surfaces. _ _ If a thick wire, provided with a ball at one end andwrth a point at thc other, be attached to the positive terminal of a statrcrnachme, practically ull the charge will be lost through the' pcrnt,'on account of the enormously greater tension, dependent on the‘rad.\us of curva- ture, Butif such awirc is atluche to one of the terminals of _the induction coil, it will be observed that with very high frequencies streams issue f.rom'the hall almost as copiouslyas from the',pornt ._ 1. _, V , _ __ _ (set ilgahnrdly conceivable that we could produce such axiondition to nn equal degree in n static machine, for thc sinipxle reason, that the tension increases as the square of the density, w ich in turn is pro- portional to the radius of curvature; hence; with a steady potential auenormous charge would be required to make streams usuo from a

THE @LlHBA§D JOURNAL AND ~"”” 24' ‘ml ELECTRICAL REVLEW. 107 polished ball while it is connected with n point, But with an induc- tion coil the discharge of which nlternntes with great mpidity, it is diifcrent, Here we hsve to deal with two distinct tendencies. First, there is the tendency to csmpc which exists in n con- dition of rest, and which depends on the radius ol curvature* nttmchzd nnd repelled, charged und discharged, snd their akin chnrgcs being thus disturbed, vihmle und emit light wnves. At the hnll, on the contrsry, there is no doubt thnt thc eiiect is to n great cxtcnt produced iuductively, the nir molecules not fieccssarily coming in contact with the ball, though they undoubtedly do so. To convince . . ,-_ ,-~ ~f"c’:- __ *~-’ ,Q ,Q ,~ ... - - ., J . , _ ,~ - T 1. _ . ‘ 13 ’ . _ ---1 » » ' - , »;_ ~-_ - 1~ -'-» -= ‘ ~__,_ _ l ., I l -4 %w?’?“” I 3 _ k ~ . - -“me Her ; ;;;f.=; _._;;' ' ct( LTL: »i=f i' Z 1 " , __ ,_ ___ __f‘ *ff* '»~,_ ;;_“- , ' , _ _ *J* / A2 fe f-= ‘-= =; L; ~ - l.-- ' ,' " i ~ =.: '-f":"1-'f-- 2 /' ,fd =<`¥f;i%i" _._ - _ _ . ,, _ . _ -v~~~ »>~f _ , ,..., 1 » -.`~,,‘,,--»vr,,_!-,.` » _ . FIG. 4.-Ssnsmvn Tmzssv ylfro. Dlscanmm 5.fFLAMlN0 Drscusnos. Flo. 6.-Srnssxunn Dxscnsnon. , _ . _ -f ..»-s, _*ac ev, _“g ` l s. ‘Q W" ~ *Z/, __,- ,__ J , _,_ ` Q ff .V - 13' __ , _ _ - _ . \ , l , ~ _ _, @‘ ‘}2°°f` ';_' 1 :_ '*=» e c f f T .,c. c e fr §§\Q____, ‘_ / _, ___ , - _“ig =_-==__;l_ __ *fi-3 ' , ‘VGA :__-T--l 'fi' A 5" i 2 Six T' “‘ if? if/' _"'??`f " ' ' - ,l -,»~ Y.-. ,._,, -_--_,. Pm."l.-Hausa AND Semv 17IG._B.4FlFTll_TY`PlOALFOl(1l F1(},9_-LU;||N0U5 1)15Cu_rR0|§_w1-m Dlson/mos. 'os Discumas. Isrnxzrossb IN.SU'LATORS._{ , _’. -mg _ _ _ ____, um ‘fum _ _ __{,;3r{1_.'_.f,“'¢ ._ _ ,w __ _ _ _ _ m f . A ¢,',?,_L;__»f _ _ , ,?_,i;5,~~¢_g| s, =‘~,_ _ _ - ‘ wa; _f;;»;=1.. ,.: - -. - l -». - ~ ag '»»-nxv§2»@}1 _ ,, \ \ _ Q5 ' _ --5 J; _L ‘ -4, A39 H, _ ; ‘ r-§-;~h_ mf wg, ' _ ., . I » :l='e~&“f'r+: - §.,,; _onine _- “_ t -2 zz. , Q4 - = _ j ; v . , / , ,, l ` _ " _ _ _ r,g;s_=,, ,:,7,W_~5,, =» ~ *~“~vrl='- - - »- - .-` Fm. ,10'4#D1scaAn0s Tnnovon Hrou- 'r Vscvryu , 31/ Fm. 11.-Pmwnssi. Dmvss sir A POWERFUL Bsusn. Flo. \2._L¢UtIlNOUS srnzsixs Escse ma Fnoxf A COT'l‘ON»COVERED \VIRE. ;;7"x~:t“' yr. F _ _ _, '<,_;1i.' _ .-_ Q J ?. ,sf ,¢‘ f ~ ‘4 \‘ V ?,, _,_ ' _ , , L '~ gs ' I’ L- _____H __ _______;_ _ _‘dx ga- ff ’i""_ _ _ _ ; __ i§ Q ' ‘ ¢, - 1 .1 -- _,Y _ ~ :M .______ . »=»--vs.a..-e~--4-wfvgi-' ’ i »7 - \» ` L-1--l .- \ - . , .;_ ir ‘ ~J7‘L,. _/ ; » ~--;fi:;~ '- _ ' » - J V Y-_-e _- 3- FI0,_;13_-Asrscrr PRESENTED nY_s ~ __ "’ "“` Y ' _vsnv Tum Wnzs Anscnsn rcs ,I~‘1a.14.`7Eri‘iccroFB.u.L‘AND`Pomr, »F‘°' 15"As"E" ‘OF Col” -UNDER TéRMlNA>L or 'rss Con. I’o\vsnsuL_BnUsu DISCHARGE: ..;'\ - " ’ , jc » , _ P' -‘mil 4" " \§¢“= _ » \ \j_;f»- l, _ _ _ fe i ‘ \ _ _~ ll 1 Z I - _ ` < . , . ' -- _ _ __ “V f ;é-¢ 'f - -f1f =2>;=?-i’c ;= _M ____ __, ___4______ i: ) fy' _"_ ' 2 f; = ~ ““ ll Il 7 »\_ _ _ , __ ~,_ ¢%l‘l“_llll ' ~-~---=- -~= _ » -» ' -~ ‘ ~ ,_ .,_\ »- ...>r> Fm. 16.-Inesnnsscssr Wms on ` "’ ”>" ” \ " F1;_.\>n:NT Smnzuso in AN Flo. `l'7A.-COIL Anmxoso Fon Pom-znrur. lll:IJ$H]C1~‘F1:(,'rS. Ussxnsusren GLo1sm\ second, there is the tendency to dissipate into the surrounding ni: by condenser action, which depends on the surface, When one of these tendencies is s maximum, the other is nt n mini- mum. At the point the luminous stream is principally dueto the nil' molecules coming bodily in contact with the point; they are ourselves of this we only need to exalt the condenser action, for instance, by enveloping thc bnll, nt some distance, by an better con- ductor, thnn the surrounding medium, the conductor being, of course, insulnted; or else by snrruumling it with n l-utter dielectric and nppronehingrsu insulated conductor; in both cnics the streams will D

'rms mnnaasemu :roummn mn 108 REVIEW. [JULY 24, 1891. break forth mom'e@piousIy. Also, the larger the lmll with u given frequency, or the higher thc frequency, the more will the bull lmve the edvnnhnge over tlxeypuint. But since R certain intensity of action is required fo lrendexvthe streams visible, it is obvious that in the experigiment described-the ball should not be taken boo large. In consequence of this two-fold tendency, it is possible to pro- duce by means of points effects identical to those produced by capacity. Thus, for instance, by nttuching to one terminal oi the coil a small length of soiled wire, presenting many points and offering great facility to escape, the potential of the coil may be raised to the snme value as by attaching to the terminal L polished ball of 1| surface many times greater than that of the wire. An interesting ex eriment, showing the eifeet of the points, may be ex-formed in the gmllowing manner: Attach to one of the terminals of Ehe coil a cotton covered wire nbout two feet in length, and adjust the conditions so that streams issue from the wirc. ln this experi- ment the primary coil should he prefemhly placed so that it extends only :bout lmlf way into the secondary coil. Now touch the free terminal of the secondary with mcoxxducting object held in the lmnd,or else connect it to an insulated body of some size. In this manner the oteutial on thc wire may be cnomxously raised. The effect of anis will be to either increase, or to diminish, the streams. If they increase, the wire is too short ; if they diminish, it is too long. By adjusting the length of the wire, a point is found where the touching of the other terminal does not _:xt sll sifcct the streams. In this osse the rise of potential is exactly cnunteracbed by the drop through the coil. It will be observed that small lengths of wire produce considerable diilerence in the magnitude and luminosity of the streams. The primary coil is placed sidewise for two reasons: First, to increase the pofcntizxl nt the wire rmd, second, to increase the drop through the coil. The scnsitivcness is thus rulglncnted. There is still another and fur more striking peculinrity of the bmsh discharge produced by very rapidly alternating currents. To observe this it is best to replace the usual terminals of the coil by two metnl columns insulated with a good thickness of ebonite. It is also well to close sll fissures :md cracks with wnx so that the brushes cannot form anywhere except at the hops of the columns. If tim conditions are carefully adjusted-which, of course, must be left to the skill of the experimenter-so that the potential rises tv :mn enormous value, one may produce two powerful brushes sevcml inches long, nearly white nt their roots, which in the dark bear ia strillin resemblance to two llsmes of agus escaping under pressure (iig.1§. But they do not only rasemlnlc, they are veritable flames, for they ure hot. Cer- tainly they nre not ns hot ss s gms burner, bu! Ihry would br xo if llw fraqzlmmy mu! I/rr palrulial 11-mild bc s|@‘l`¢-1'r1zIIg/ I1 ig/L. Produced with, say, twenty thousand slternntiuns pct second, the heat is easily per- ceptible even if the potential is not excessively high. The heat developed is, of course, due to the impact of the sir molecules against the terminals and against ench other. As, nt the ordinary pressures, the menu free path is excessively small, it is possible that in spite of the enormous initial speed impsirted to ezmlm molecule upon homing in Contact with the tern\iun.l, its progress-by collision with other molecules-is rcinrdrd to suvh nn extent, tlmt it does not get away far from the tcrmiunl, but nmy strike the same umuy timcs in succession. The higher the frequency, the less the mulc- culc is able to get sway, and this the more so, as fur a given eilect the potential required is smnllcr: and 11 frequency is conceivable -perhaps even obtninnlylc- nt wlxirh practically the same molecules would strike the Ierminal. Under such conditions the exchange of tlxe~molcculcs would be very slow, :md the heat produced at, and very near, the terminal would be excessive, But if t e frequency would go on increasing c<\ustn|\tly, the heat produced would begin to diminish for obvious reasons. In the positive brush of n static machine the exclmnge of the molecules is very rapid,tl1e stream is constantly of one direction, :md there nrc fewer collisions ; hence the heating eEect must be very small. Anything that impairs the iacility of exchange tends to increase the lnenl bent produced. Thus, if a bulb be held over the terminal of the coil so :Ls to enclose the brush, the sir contained in the bulb is very quickly brought to n high bempemkure. If :\ glass tube be held over the brush so new allow the draught to vnrry the lu-ush upwnnls, scorching hot air escapes at the lop ni thc tube. Anything held within the brush is, of course, rapidly lmntcd, and the possibility of using such heating effects for some purpose or other suggests itself. When contemplating this singular phenomenon of the hot brush, we cannot lmlp lxeinu cux\\'iu<‘<-d tlmt n similar process must lake plnce in the ur<\i|\:\ry Hmm-, and it secnxs strange that after all these centuries past of familiarity with the Ilnznc, now, in this cm of elec- tric lighting and lxcntiug, we are (innlly lcd to rccouniw, that since time immcumrinl we lmvc, after ull, always had “electric light and heat" at our disposal. It is nlso of un little interest to con- possiblc Wny of pmduuing-by template, that we have s other tlmn clicmivnl m<~m\s-:\ vcrihxlvlc ilame which would give umtcrinl being consumed, without light and heat \\'itl\o\1t :my any rzllmuiczml provcss faking place, and to necomplish this, we only need to perfect methods of producing enormous frequencies and pu!eulin.ls, I have nn dmlht that if the potcntinl could be made to alternate with suflicieut rapidity nnd power, the brush lormed at the end of s wire would lose its electrical characteristics and would become finmelike. The tlnme must be due to electrostatic molecular action. This phenomenon now explains in s manner which can hardly be doubted the frequwnt n:':~i

THE TEKIUBAPHID' JOUB-KAL AID ELLCTRIGAL REVIEW. UU” 11' 1891-3 EXPERIMENTB WITH ALTERNATE CUR- RENTS OF VERY HIGH FREQUENCY, AND THEIR APPLICATION TO METHODS OF ARTIFICIAL ILLUMINATION.° BY NIKOLA TESLA. (U:/nli1z|1c¢l_/`1'|//u page 108,) Tum above plan necessitates the employment oi n primary of ~:om~ parutivcly small size, and it is apt to hcuxt when powerful cilects are desirable for rs ccrtnin length of time In such u case it is bette to . r employ slnrgcr coil, Hg. 178, and introduce it from one side oi the tube, until the streams begin to appear. In this case the nearest terminal of th - dn ~ ` e sewn ry may be Lounccted to the primary nr to the ground, which is practically the same thing, il the primsry is con- ' A lccturo delivered before the American Institute of Electrical Engineers, nt Columbia College, N.Y., May 20th, 1891.

TIHJ TELEGBAPBIO JOURNAL ARD 148 ELECTRICAL REVIEW. nested directly to the mar-liine. In the case of ground connections it is iv'-ll to dm-turinine experimentally the frequency \\‘hieh‘is best suited under the vovidirimus of the test. Another way of obvinling the strcnrns, more or less, is to ninkc the primary in sections nnrl supply it from separate \\'(-ll insulated sources. In nmny of these experiments, when power-iul ellects arc wanted for a short time, it is :uh nntagenus to use iron cores with the rimarics. ln such case a very large primary coil may be wound and pliwced sido hy side \\ith the svr:m\lla|'y, nnd, tho nearest tcrminnl of the latter heing v-onn<-f~tcrl to the primnry, n laminated iron core is introduced through the primary into the secondary as far as the streams will pennit. Under these conditions |\n excessively o\\'crIul brush, several inches long, which may be appropriately cnlltd “ St. EImo's 1 , / t\, 0 U my I lllll "l k to Wddlhddhf Fil., 17n~ Con. Airnasizrair r-*on Powsnruri Bnusn Errr:c'rs.~ ST. ELaw‘s lIo'r Fuzrz. hot tire,” may be caused to appear nt the other terminal of the sevorirlary, prorluv-ing striking eflerts. lt is a most powerluloznniser, so powcrlul, irnlr-cd, that only a fc\\' minutes are sullicicnt to till the whole room with the smell oi ozone, and it undoubtedly possesses the quality of exciting chemical nflinitics. For thc production of ozone, alternating currents of very high frequency are eminently suited, not only on account ol the advan- tages they oilcr in the way of conversion, but also bernuse ot thc fact, that the ozcnising action of a rlisebm-ge is dependent on the frequency as well as on the potential, this being undoubtedly connrmcd by observation. in these experiments, if an iron core is used it should bc carefully ivatclretl, as it is apt to get excessively hot in an incredibly short time. To gi\\: :in idea of the rapidity of the heating, I \vill state, that by passing n po\\'cr[ul current through n coil with many tums, the inserting \\*ithm the same of a thin iron wire for no more than one sceornl`s time is suflicient to heat the wire to something like iO() U. ' ljut this rapid heating does not need to discourage us in the use of iron cores in connection with rapidly alternating currents. I have for along time been convinced, that in the industrial distribution by means of transformers, some such plan as thc following might be practicable. \\`e may use a comparatively small iron core, sub- flivideil, er perhaps no( cvcn subdivided. We may surround this core with a c

'rms 'rEr.x0BAPR1D< JOURNAL AID JULY *"» 1891-3 ELuofrRicA_L REVIEW. 149 magnetic waves many times longer than those of light, andproducible by sudden discharges of a condenser, could not be utilised, it would u-cm, except we avail ourselves of their effect upon conductors as in the present methods, which are wasteful. \Ve could not aifect by means of sneh waves the static molecular or atomic charges of a gas, muse them to vibrate and to emit light. Long transverse waves cannot, apparently, produce such effects, since excessively small electromagnetic disturbances may pass readily through miles of air. Such dark waves, \n\1ess they are of the length of true light waves, cannot, it would seem, excite luminous radiation in a Lleissler tube, and the luminous effects, which are producible by induction in a tube devoid of electrodes, I am inclined to consider as being of an electi - static nature, 'lb produce such luminous effects, straight electrostatic thrusts are required; these, whatever be their frequency may disturb the molecular charges and produce light. Since current impulses of thc required frequency cannot pass through a conductor of measurable rlnnensions, we must work with a gas, and then the production of piweriul electrostatic edects becomes an imperative necessity. - It has occurred to me, however, that electrostatic effects are in nanny ways available for the production of light. For instance, we may place a body of some refractory material in a closed, and pre- lurably more or less exhausted, globe, connect it to a source of high, nipiclly alternating, potential, causing the molecules of the gas to strike it many times a second atenormous speeds, and in this manner, with trillions of invisible hammers, pound it until it gets incan- descent; or, we may place a body in a very highly exhausted globe, in 14 non»siriking vacuum, and, by employing very high frequencies and potentials, transfer suiiicient energy from it to other bodies in the vicinity, or in general to the surroundings, to maintain it at any degree of incandescencc; or, \ve may, by means of such rapidly alter mixing high potentials, disturb the ether carried by the molecules of a gas on their static charges, causing them to vibrate and to emit li ht. llutiialectrostatic eriects being dependent upon thc potential and frequency to produce the most powerful action, it is desirable to in- crease both as far as practicable, It may be possible to ohtain quite fair results by keeping either of these factors small, provided the other is sutlicienily great ; Init we are limited in' both directions. My experience demonstrates that \ve cannot go below a certain frequency, lor, iirst, the potential then becomes so great that it is dangerous; and, secondly, the light production is less cilicienr. I have found that, hy using the ordinary low frequencies, thc pliysiolo;-giciil eilect of the current required to maintain at a certain decree of brightness a tube 4 feet long, provided at the ends with eatsale and inside condenser coatings, is so powerful that, I think, it might produce serious injury to those not accustoinedto such shocks; whereas, with 20,000 alternations per second, the tube may te maintained at the same degree of brightness without any eifect being felt. This is due principally to the fact that 1-i much smaller potential is required to produce the same light eliect, and also to the higher ethciency in the light production. It is evident that the ellieieney in such cases is the greater the higher the frequency, for the quiukerthe process of charging and discharging the molecules, the less energy will be lost in the form of dark radiation. But, unfortu- nately, we cannot go beyond n certain frequency on account of the ililiiculty of producing und conveying the clients. Ihave stated above that n body enclosed in an uncxhansted bulb may he intensely heated by simply connecting it with a source of rapidly alternating potential. The heating in such a case is, in all probability, due mostly to the boinburdinent of the molecules of thc grstonfiiaca ai the nat. when nic nut is errant:/ea,i1»c heating el the body is much more rapid, and there is no dilliculty whatever ui bringing a wire or iihnnent to any degree of incandescence by simply connecting it to one terminal of a coil of the proper: dimen- in/ns. Thus, if the well-kuoivn apparatus of I’rof.QCrookes,{consist- mg of a bent platinum wire with vanes mounted over it (fig.|l9),[be /\ in-5; /fi \ \s§» l ,AN Q ,\ , F ,J ,_ ~ i LJ Y l M s l~‘io. 10.-'l‘nn Cnoounn EX\’|il\I||lN'l‘ on Oifizn (ilncurr. connected to one terminal of the coil-either one or both ends of the platinum wire being connected-the wire is rendered almost instantly incandescent, and thc mica vanes are rotated as though a current imui a battery were used. A thin carbon filament, or, preferably, u lairlon of some reimctory material (Iig. 20), evcn if it be acoinpnm- tively poor conductor, cnclusud in nn cxhnilsted globe, nmy be rcn~ dared highly incandescent; and in this umnncr nsimplc lamp, capable of giving any desired candle-power, is~provided, 'l’h<: success of hnnps of this kind would depend largely on the selection of the light-giving bodies contained within the bulb. Since, under the conditions described, refractory bodies~\\'hich are very poor conductors, and capable ol withstanding for a lung time exces- sively high degrees ol tcmpenitum-may be used, such illuminating devices may be rendered successful It might he thought at first that if the bulb, containingthe Element or button of refractory material, be perfectly well exhausted-that is, as far as it can be done bythe use of the best apparatus-the heating would be much less intense, and that in a perfect vacuum it could not occur at all. This is not confirmed by my experience; quite the ountrary, the better the vacuum the more easily the bodies are brought to incandesecnoe. This result is interesting for many l'€|'lSOi`|B. At the outset ol this work the idea presented itself to mo whether two bodies of refractory material enclosed in a bulb exhausted to such a degree that the discharge of a large induction coil, operated in the usual manner, cannot pass through, could he rendered incandescent by mere condenser action. Obviously, to reach this rcsult enormous potential diiferences and very high frequencies are required, as is evident from a simple calculation. But such a lamp would possess a vast advantage over an ordinary incandescent lamp in regard to efticiency. It is well known that the eliiciency of a lamp is to some extent is function of the degree of incsndescence, and that, could we but work a iilament at many times higher degrees of incaudescenee, thc ciliciency would be much greater. In an ordinary lamp this is impravticablc 1 fl /i ./' 2 'E ; 7 /' ` _ 1_1 5 5 / \\ if 5 ' / '?`, i ii / 1 , \,)/ . \ ' f 1* l~ , / L-f ~ - i I Fm. 21.-Lane wrrn Two Fins' Fin. 20.-Lani' wrrn Sumu; srnivrs rn Hiounsr Vacoou Brlocir on Rnvmcroar lisrnann, wrru Lsanms-in Winns. on account of the destruction of the tilameut, and it has been determined by experience how far it is advisable to push the in- candesoence. It is impossible to tell how much higher ellicieney could, be obtained if the iilament could withstand indefinitely, as the investigation to this end obviously cannot be carried beyond n certain stage; but there are reasons for believing that it would be very considerably higher, An improvement might be made in the ordinary lamp by employing a short and thick carbon; hut then the leadiug»in wires would have to be thick, and, besides, there are many other considerations which render such a modification entirely impractiouble. But in a lamp as above described, thc lead- ing-in wires may be very small, the incandescent refractory material may he in the shape of blocks odering a very small radiating surface, so that less energy would be required to keep them at the desired in- candeswnce; and in addition to this, the refractory material need not be carbon, but may be manufactured from mixtures of oxides, for instsnee, with carbon or other material, or may be selected from bodies which are practically noirconductors, and capable of with- standing enormous degrees oi temperature, All this would point to the possibility of obtaining ax much higher eiliciency with such a lamp than is obtainable in ordinary lamps. in my experience it has been demonstrated that the blocks are brought to higi degrees of incnndescence with much lower potentials than those determined by calculation, and the blocks may be set at greater distances from each other. We may freely assume, and it is probable, that the molecular bombardment is an important element in thc heating, even if the globe be exhausted with the utmost care, as I have done; for although the number of the niolcculcs is, \_-oinpuia» tively speaking, inalguilleunt, yet on account of tha mean irce palh being very grcnt, there are fewer collisions, and the molecules may reach much higher speeds, so that the heating eifcct due to this cause may be conszdmtle, as in the cronies @>

TIIE TE[XBBLPmc‘ JUUBHAL ‘HD i 150 ELECTRICAL REVIEW. UU" '”’ ml' rig. 22, have been constructed and operated by me, and investi- gations are being carried on in this line. There is no diliculty in reziuhing such high degrees of iueandcscence that ordinary carbon is to all appearance melted and volatiliscd. If the vacuum could bc made absolutely perfect, such n lamp, although inoperative with apparatus ordinarily used, would, if operated with currents of the required character, zxllord an illumiunnt which would never be destroyed, and which would be fm- more eliicient than an ordinary in- candescent 1amp_ This perfection can, of cnurse, never be reached, and :\ very slow destruction and gradual diminution of the size always occurs, as in imzandnsecnt lamps; but there is no possibility cf a sudden and premature disabling which occurs in the latter by the breaking Of the Hlnmcnt, espccial1_y|when the incandescent bodies are is felt, being due to the nttraction :md repulsion of the molecules of the air \\'liicl.\ are electrified by induction through the glms. In some cases, when the action is very intense, I have been able to bear n sound, which must be due to the sumo cause. \VlJe1\ the :\lL<:rnations are low, one is apt to gctzxu excessively powerful shock from the bulb. lu general, when one nthiches bulbs or objects of some size to the terminals of the coil, one should look out for the rise of potential, for it may happen that by merely con< necting :i bulb or plate to the teru\in:\1,tl.\c potcutinl mny rise to many times its origiunl value. When llnmps nrc :\tt:xuhcd to the terminals, as illustrated in fig, 24, then the capacity of the‘l»u1bs should be such n the slmpc of blocks. ff- ,`7`\ 1- _:é i V, = 2 ;f W “I , ;?ff:_i;`:"'fT'Tf`i I if? Efél 5 ly I; *ug ;§ 2 ff l Vi I 351' l l' ` ' Fm. 24.-LAMPS wrru ONE Lmnms-LN Wim: Rmwznzn , , F ' INCANDESCENT, , l ` _ as to give thc mzxxiuinm rise of potential under the existing condi- ; -l ' tions. In this Luzmucr one may obiaiu the required potcutinlvvibh ` fewer turns of wire. The lift: of such lmups as described above depends, of course, ‘A largely mu (hc degree of cxhmistiou, but Ko some extent also oil the slmpu oi thu Imlock of refractory material. Thcoret,ical.ly it FIG- 22- would scum that a small sphere of carbon enclosed in a sphere nf LAMP wxzm Two Rmmucroiw Bnocxs rn Hxuumsr VAUUUM. With these rapidly alternating potentials there is, however, no necessity of enclosing two blocks in a g1ube,but a single block, as in iig. 20, or Hlzxmcnt, Hg, 23, may be used. The potential in this case must of course bc lxiglicr, but it is cnsily obtainable, and besides it is not necessarily dnugerous. The facility with which the button or lilamcnt in such A lamp is brought to incaudesccnue, other things being equal, depends on the size of the globe. If in perfect vacuum could bc obtained, the size of the globe would not be of importance, for then the heating would be QQ E512 74 \ % X / l l F P 1 / Y 7 %; f f,;;?~ x 2/ / \ I l 4 Fir.. 23.fLrii11- wma Smauc Srmlcur FILAMENT Am; ONE Lmnmo-IN Wmm. wholly due to the surging of the charges, and all the energy would be given off to the surroundings by radiation. But this can never occur in practice. There is always some gas left in the gIolxe,smd although the exhaustion may be carried bo the highest degree, still the space inside of the bulb must be considered as conducting when such high potentials are used, :md I assume that, in estimating the energy that may be given ol! from the filament to the surroundings, We may consider the inside surface of the bulb as one coating of a condenser, the air and other objects surrounding the bulb forming the other coating. When the nlternations are very low there is no doubt that a considerable portion of the energy is given oll" by the electrification of thc surrounding nlr. lu order to study this subject better, I carried on some experi- ments with excessively high potentials nnd low frequencies. I then observed that when the l.\:iu<1 is approached to the bulb-the filament being connected with one terminal of the coil-a powerful vibration glass would not sulfer deterioration from molecular bombnrdnieulgfor, the matter in the glnbc being mdinnt, the molecules would move in straight lines, and would seldom strike the sphere obliquely. An interesting thought in corincction with such a lamp is that in it “ elec- tricity ” and electrical energy nppnreutly must move in the Bam! lines. The use of alternating currents of very high frequency makes il possible to transfer, by electrostatic or eleutrd-mnguetic induction through the glass of a lamp, suliicient energy to keep a filament at iucamlcscexxce :md so do away with the leading-in wires. Such lamp! have been proposed, but for want of proper apparatus they have uoC been successfully opemtcd, Many forms of lamps on this principle with continuous and broken filaments have been constructed by me and experimented upon. When using a secondary enclosed within the lamp, a condenser is advantageously combined with the secondary. When the transference is eliected by electrostatic induction, the potentials used arc, of course, very high with frequencies obtainable from zi m:icl\im:. For instance, with a condenser surface of 40 v:cuii» ruetrcs square, which is not impmebicnbly large, and with glass nl guud quality 1 mm. thick, using currents alternating 20,Q00 times I second, the potential required is approximately 9,000 volts. This may seem large, but since each lump may be included in the secondary dl :\ transformer of very small dimexisions, it would not beiuconvcuicnb, and, moreover, it wuulrl not produce fatal injury. The tmusformcn would all be preferably in series. The regulation would offer no dilliculties, :us with currents of such frequencies it is very eaayta maintain a constant c\\rrc1.\t. In the accompanying engravings some of Lhe types of lamps of this kind are sho\vn. Fig. 25 is such a lamp with a broken filament, and if l I N' Fm, 25.~LAMP wrru Two BLOCKS on FILAMENTS AND A PAB ol hwni-ENDENT INSXDE ANU Oursmn Colm!-INSER (lonxxss. lig. 26/\ and 2Gn one with n single outside and inside coating und | single Iilamcnt. I have nlso nizule lamps with two outside :uid lnnlde contimgu :uid :x \:uu\\iu|\<.»uu loop cunuputing the latter. Such lump have been operated hy mc with current impulses of the uuormoul frequencies olitaiuzilile by the disruptive discharge of condeusers. The disruptive discharge of :L condenser is especially suited for operating mich lamps-with uu orrhvaré eluc¢»rica1»cunuectious-by

JULY 3] 18913 'rua 'ylfrxannrlno Jouluul. AFD 5 ' ELEQIRICAL REVIEW means oi electro-magnetic induction, the electro-magnetic inductive :tests being excessively high : and I have been able to produce the desired ineandescence with only n few short tums of wire. Incandes- fnlce may nlsnbe prodiwed in this manner in a simple closed fila- ment l. :V '7 ` i i . X - - 5 _ r Y! / ,_ J W/ . "I i \1i,, l /]\\` l` l | "ln i li ~ - yn l ` l l~ *~ .2 iw l . if i lfdlldl iflfy. l\ § ,» in | , by éffli .1 __<- iii;-l FIG, ‘26.\. FIG. 26s. Linn WITH ONE Flmunxrr, Om Inslnn AND ONE Ourslnn Conunnsnn. Comma, Leaving nmv out of consideration the pmcticability ot such lamps, lwculd only sny thnt they possess s beautiful and rlesirnble feature, namely, that they can be rendered, at will, more or less brillinnt V ~;i*‘1f ;- ~- -- -, r/ T iii ` " `\ l ,__ » ' f l _ , J V F1o.27.-LAMP wrru ONE Frm- Fm. 28.-LAMP wrrn Om-2 Fru- usm inn Lmnmo-nz Winn umm, Ons Insms /lun Ou: inn Ex1‘ExnuL 'Corinnnsnn Orrrslnn Connnnsxn Con'- Cusrmu. ma, nm /\uxIu.4nY Corrnm nmply hy altering the relative position of the uutalde and inside condenser coatings, or inducing and induced cimuita. When n lamp is lighted by connecting it to one terminal only of thesoiu-cc, this nmy he facilitated by providing the globe with un outside condenser coating, which serves at the mme time ns n re- flector, and connecting this to an insulated body of some sine. 1 ` ’ `\ i l \` t- `| _:_ ' ' \ - _ l in I Fm. 29.-lrlcnmsxna 'rlll Bmnumuy ol' Lum on Orin Winn. Lamps of this kind nm illustmted in ill. 27 and tlg, 28. Fig. 29 shows the phxn ot connections. The brilliancy of the lamp muy, in tlnicfise, be regulated within wide limits by varying the size of the insulated metal plate to which the coating is connected. (To he amlimud.)

'nm TEKIGBAPHIB- JOURNAL AID 176 ELECTRICAL EXPERIMENTS WITH ALTERNATE CUR- RENTS OF VERY HIGH FREQUENCY, AND THEIR APPLICATION T0 METHODS. OF ARTIFICIAL ILLUMINATION ‘ BY NIKOLA TESLA. [f7om'Iv1¢Ird/rmn page 151.) It is likewise pmcticriblc to light with one lending wire lamps siich ns illustmtcd in fig. 21 and rig. 22, by connecting one ter- minal of the lamp to one terminal of the source, nnd the other to nn iusulnted body of the required size. In all cases thc insulated body serves to give off the energy into the surrounding space, and is equivalent to rs return wire. Obviously, in the two last-named eases, instead of connecting the wires to an insulated body, connec~ tions may be mnde to the ground. The cxpcriments which will prove most suggestive, and of most interest to the investigator, are probnbly those performed with ex- hausted tubes. As might be anticipated, a source 'of such rapidly alternating potentials is wpable of exciting the tubes at s consider- able distance, and the light elfects produced are remarkable. ‘ During my investigations in this line, I endeavoured to excite tubes, devoid oi any electrodes, by electro-magnetic induction, making the tube the secondary of the induction device, and passing through the rimary the discharges of a Leyden jar. 'These tubes were m_ade ofpmnny shapes, and I was able to obtsin luminous effects which I thcn thought were due wholly to electro-magnetic induction. But on oarelully investigating the phenomena, I found thht the edccts produced were more of an electrostatic nature. It may be attributed to this circumstance ‘that this mode ol exciting tubes is very wasteful, namely, the rirnary circuit being closed, the potential, and consequently the elecgrostatic inductive etlect, is ,much dimi- nishcd. When an induction coil, operated as above described, is used, there is no doubt that the tubes are excited by electrostatic induction, and that electro-magnetic induction has litt e, it anything to do with the phenomena. This is evident from many experiments, For instance, if a tube be taken in one hand, the observer being near the coil, it is brilliantly lighted and remains so, no matter in what position it is heldrelatively to the observers body. Were the action electro-magnetic, the tuba could not be lighted when the obser'ver‘s body is interposed between ' A lecture dcli\'c'n:\'l before the American Instituto #Electrical Engineer; ra oemmbn onusgs, mr, my sour, ram. _ , REVIEW' [Auovsr 7, 1891. it and the coil, or st least its luminosity should be .wnsidenbly diminished. When the tube is held exactly over the centrebf the coil-the latter being wound in sections, and the' primary placed symmetritnlly to the secondary-it may 'remain completely dark, whereas it is rendered intensely luminous by moving it s ightl to the right or left lrom the centre of the coil. It does .not light, because in the middle both lialves of the coil neutzralisc each other, and the electric potential is nero. If the action were electro-magnetic; the tube should light best in the planethrough the centre of the coil, since the electro-magnetic etlect there should be s maximum, When nn sro is established between the terminals, the tubes and lanrps in the vicinity of the coil go out, but light up again when the src is broken, on account of the rise of potential. Yet the electro-magnetic effect should be practically the same in both cases. By plscingatube at some distance from the coil, and nearer to one terminal--preferably at a point on the axis of the coil-one may light it by touc ing the remote terminal with an insulated body of some size or with the hand, thereby raisinglphe potentinl at that terminal nearer to the tube. If the tube is s ' ted nearer tu the coil so that it is lighted by the action of the nearer terminal, it may be made to go out by ho ding, on an insulated support, the end of n wire connected to the remote terminal, in the vicinity of the nearer ter- minal, by this means counteracting the action oi the latter upon the tube. These effects are evidently electrostatic. Likewise, when s tube is placed at a considerable distance from the coil, the observer may, standing upon ln insulated support, between coil and tube, light the latter by approaching the han to it; or he may even render it luminous by simply stepping between itnnd the coiL This would bc impossible with electro-magnetic induction, for the body of the ob- server would act as a screen. r When the coil is energised by excessively weak currents, the ex - rimenter may, by touching one terminal of the coil with the tub; extinguish the latter, and may again light it by bringing it out of contact with the terminal and allowing a small arc tn form. This is clearly due to the respective lowering and raising of the potential at that terminal. In the above experiment, when the tube is lighted through a small arc, it may go out whentbe arc is broken, because the electrostatic inductive etlect _alone is too weak, though the potential may be much higher; but when ‘the are is established, the electriliestion ofthe end of tha tube is much greater, and it conse- quently lights. ' ' ' f If n tube is lighted by holding it near to the coil, and in the hand which is remote, by grasping the tube anywhere with the other hand, the part between the hands is rendered dark, and the singular effect of wi ing out the light of the tube may be produced by ssing the grind \}uiclrly along the tube, and at the same time with~ sgawing it gently rom theoorl, judging properly the distance so that the tube remains dark afterwards. ` ' If the rimary coil is placed sidewise, as in fig. 175 for instance, and an exhausted tube be introduced from the other side in the hollow space, the tube is lighted most intensely because of the increased condenser action, and in this position the striaa are most sharply defined. In all these experiments described, and in many othex~s,tbe action is clearly electrostatic. The elfects of screening also indicate the electrostatic nature of the phenomena, and show something of the nature of electrification through the air. ` For instance, ii s tube be placed in the direction or the axis of _the coil, and an insulated metal plate be interposed, the tube will generally increase in or if it be too far from the coil to' li ht, it ma` even be reudere *luminous by interposin an insulatef metal phtc. The magnitude of the effects depends to some extent on the size of the plate. But if the metal plate be con- connccted by a wire to the ground, its interposition will always make the tube go out, even if it be very near the coil. In general, the inter position ol a body between the coil and tube increases or diminishes the brilliancy of. the tube, or its facility to light np, according to whether it increases or diminishes the electritlcation. When experi~ menting with an insulated plate, the plate should not be taken too lurgc, else it will generally produce a weakening effect by reason of its rest facility for giving otf energy to the surroundings. 1% a tube be lighted at some distance from the coil, and a plate ol hard rubber or other insulating substance be interposed, the tube may be made to go out. The interposition of the die ectric in this ease only slightly increases the inductive effect, but, diminishes consider- ably the electrification through the air. ` In all the cases, then, when we excite luminosity in exhausted tubes by means of such s coil, the eEect is dus to the rapidly alter- nating electrostatic Ipptential; and, furthermore, it must be attributed to the harmonic a rnation produced directly by the machine, and not to any superimposed vibration which might be thought to exist. Buch superimposed vibrations are impossible when we work with an alternate current machine. I! a spring be gradually tightened and released, it does not perform independent vibrations ; or this s sudden release is necessary. So with the alternate currents hom a dgnamo machine; the medium is harmonically strained and release , this giving rise to only one kind of waves; n sudden contact or break, or a sudden giving way of the dielectric, as in the disruptive dis- charge of a Leyden Jar, are essential for the production of superim- posed waves. ` In all the last described experiments, tubes devoid of any elec< twdes may be used, and there rs no ditdculty in producing by their means sulicient light to read by. The light ediect is, however, con- siderably increased by the use of plrosphoreseent bodies such as yttris, uranium glass, M. A ' dilllculty will be found when the phosphorescent material is used, lor with these powerful eiieots it is carried gradually away, and it is preferable to use material in the form of a soli . _ A Iulteod ot de ndin on induction at A distance to light the tube, the same may bg progided with an external-and, il desired., also with an internal-condenser coating, and it may than be suspended

7, EL‘§Ca'§;a"r1;°'*1e~ee‘W_ anywhere in the room from a conductor connected to one terminal uf the coil, and in this manner s soft illumination may be provided. The ideal way cf lighting a hall or room would, however, he to produce such a condition in it that an illuminating device could be moved and put anywhere, and that it is lighted, no mutter where it is put and without being electritmlly connected to anything. I have been able to produce such a condition by creating in the room a powerful, rapidly altemuting electrostatic iield. For this purpose I suspend a sheet of metal a distance fmm the ceiling on insulating cords and connect it to one terminal oi the induction coil, the other terminal being preferably connected to the ground. Or' else I suspend two sheets as illustrated in il . 30, each sheet being connected with one ol the terminals of the coiE and their size being carefully determined. _An exhausted tube may then be carried in the hand anywhere between the sheets or placed anywhere, even a certain distance beyond them ; it remains always luminous. In such an electrostatic Held interesting phenomena may be observed, especially if the alternations are kept low andthe potentials excessively high, In addition tothe luminous phenomena mentioned, one may observe that any insulated conductor gives sparks when the hand or another object is approached to it, and the sparks may often be powerfuL When a large conducting object is fastened on an insu- lnting support, and the hand approached to it, a vihmtion, due to the rythmica motion of the air molecules is felt, und luminous streams may be perceived when the hand is held near a pointed projection. When a telephone receiver is made to touch with one or both ol its terminals an insulated conductor of some size, the telephone emits a loud sound; it also emits a sound when a length of wire is attached to one or both terminals, and with very powerful fields a sound may be perceived even without any wire. How far this principle is ca ahle of practical application, thefutum will tell. It might be thought that electrostatic effects are unsuited for such action at a distance. Electro»mn ctic induc- tive eiiects, if available for the production of light, might be thought better suited. It is true the electrostatic effects diminish nearly with the cube of the distance from the coil, whereas the electro- meaus of a conducting circuit, the energy to the lace of transforma- tion. Bat in so doing we cannot very sensibly d)epart from present methods, and all we could do would be to improve the ap aratiis. From these considerations it would scum that if this igeal way of lighting is to be rendered practicable it will he only by the use ol electrostatic effects. In such a case the most powerful electrostatic in~ ductive effects are needed; the apparatus employed must, therefore, be capable of producing high electrostaticpoteutials changing in value with extreme rapidity. High frequencies are especially wanted, for gracticnl considerations make it desirable to kee down the potential, y the employment of machines, or, geuer-allJy speaking, of any mechanical apparatus, but lou* frequencies can be reached; recourse . ' rf " ~\ I < ‘ l \ i 1 , p, |> , H r \ jf »_-_,W-_Q l L V_)l` l _L l _ _ \\_f_/ F1n.31.-Discuss! or-‘ Corvrmcrrons Fon Couvsrvrmo Fnolu Hma To Low Tlrristoxi nv Mamas or 'nm Dlsnurrrvm Dxscr-lsnom. miut, therefore, he had to sonic other means, The discharge of a con- denser aifords us a menus of obtaining frequencies by far higher than are obtainable nicchzuiienlly, and I have accordingly employed con~ denscrs in the experiments to the above end. l When the terminals of a high tension induction coil, (lg, 81, are connected to a Leyden jar, and the latter is discharging disruptively ___ i__ ._/3 V , $15 I lil W ll; .ll 'Wi wi Fm. 30.-Inner. Mm-non or' Lxonruvn A Room.-Tunes Davorn os sur ELEC-moons Rmrvnaanu Barnnnnrr m sn AL'rs:ns.\-rum Enecraosrirxo FIELD. magnetic inductive effects diminish simply with the distance. But when we establish an electrostatic field of force, the condition is very diiierent, lor then, instead ot the differential effect of both the terminals, we get their conjoint effect. Besides, I would call atten- tion to the fact, that in an alternating electrostatic field, n conductor, such as an exhausted tube, for instance, tends to take up most of the energy, whereas in an electro- magnetic alternating held the conductor tends to take up the least energy, the waves being reflected with but little loss. This is one reason why it is djfllcult to excite an exhausted tube, at a distance, hy electro-magnetic induction. I have wound coils of very large diameter and of many turns of wire, and connected a Geissler tube to the ends of the coil with the oh`ect of exciting the tube at a distance; but even with the powerful inductive effects producible by Leyden jar discharges the tube could not be ex- cited unless at a vary small distance, u though some judgment was used as to the dimensions ol the Foil. I have also found that even' the most powerful Leyden jar discharges are capable of exciting only fccble luminous eiiects in a closed exhausted tube, lud even these effects upon thorough examination I have been loroedto consider of an electrostatic nature. ~ How, then, can we hope to produce the required effects at a disuince by means of electro-magnetic action; when even »in the closest proximity to the source of disturbance, under the most advantageous conditions, wc can excite but faint luminosity? It is trac that when acting at a distance we have the resonance to half us out. We can connect an exhausted tube, or whatever the illum noting device may be, with an insulated system oi the proper capacity, and so it may he possible to increase the effect qualitatively; and on y qua1itatively,f0r we would not get more energy through the device. Y S0 we-luny, by resonance effect, obtain the requiredeleetromotive force in nu ex- hausted tube, and excite faint luminous eifocts, but we cannot get enough eneriyutéo render the light practicalty available, and a lim le aslculstion, d on experimental results, shows that even if, all Phe' energy which a tube would receive at e certain distaucelmm the. source should be wholly Converted.; into light, it would hardly sstisfyf the practical requin-ments. Hence the necessity qi directing, by; into a circuit, we may look upon the arc playing between thc knobs as heingn source el alternating, or generally speaking, undulating currents, mul then \ve have to deal with the familiar system of a generator of such currents, a circuit connected to lt, and a. condenser bridging the circuit. The condenser in such a case is ri veritable transformer, and since the frequency is excessive, almost any ratio in the strength of the currents in both thu branches nrhy be obtained, Ia reality tho analogy is not quite complete, for in the disruptive dis< charge we have most generally a fundamental instantaneous variation of comparatively low lrequency, and a superimposed harmonic vibm- tion, and the laws governing the [low of currents are not the same for both. , E V I l , ‘ I ` ` r _ ,_:..;Qr , .I l ' ' '"? - T-V ,' | " 'W S ' ' W", ‘ z Fra. 32.-Mirman or Opnarrluo su Isnucvxox Con. In converting in this manner, the ratio ol conversion should not be toograat, lor the loss in the arc hetwecn the knobs increases with thv square of the current, and if the jar be discharged through very thicl and short conductors, with the view of obtaining a very rapid oscilla tion, a very considerable portion ol the energy stored is lost. On the other hand, two small ratios are not practicable for many obvious reasons, As, the converted , currents How in u _practically closed circuit, the

'HIE 'A'l:r.lGBAPRID\.1UUBx|aL AKD [Auousr 7 1891. 178 ELncfrR1cA_L REVIEW. ' electrostatic effects are necessarily small, and I therefore convert them into currents or eifects of the required character. I have edected such conversions in several ways. The preferred plan of connections is illustrated in fig. 32. The manner of operating renders it easy to obtain by means of n small and inexpensive ap aratus enormous diitercnces of potential which have been usually obtained by rncnns of large and expensive coils. For this it is only necessary to tnkc an ordinary small coil, adjust to it a condenser and discharging circuit, forming the primary of an auxiliary small coil, and convert upward. As the inductive effect of the primary currents is excessively great, the second coil nccd have comparatively but very few turns., By properly adjusting the elements, remarkable results nfay be secured. ln endeavouring to obtain the required electrostatic effects in this manner, I have, as might be expected, encountered many difficulties which I have been gradually overcoming, but I am notns yet prepared to dwell upon my ex erienccs in this direction. I believe that the disruptive discharge of a condenser will play an important part in the future, for it offers vast ossibilities, not only in the way ol reducing light in a more eilicient) manner and' in the line indicated by theory, but also in many other respects. For years the eiforts of inventors have been directed towards ob- taining electrical energy from heat by means of the thennopile. It might seem invidious to remark that but few know what is the real trouble with the thermopile. It is not the inefliciency or small out- put~thongh these are great drawbacks-but the inet that the ther- ruopile has its phylloxem, that is, that by constant use it is deterio- rated, which has thus far prevented its introduction on an industrial scale. Now that all modern research seems to point with certainty to the use of electricity of excessively high tension, the question must present itself to many whether it is not possible to obtain in a practicable manner this form of energy from heat. We have been used to look upon an electrostatic machine as a plaything, and some- how we couple with it tl\e idea of the inetiioient and impractical. But now we must think diiicrently, for now we know thateverywhere we have to deal with the same forces, and that it is a mere question oilinveuting proper methods or apparatus for rendering them avail- ah e. In the present systems 01 electrical distribution, the employment of the iron with itsyvonderful magnetic properties allows us to reduce considerably the sire ol the apparatus; but, in splite of this, it is still very cumbersome. i'l‘he more we progress in t e study of electric and magnetic henbmena, the more we become convinced that the present method)s will be short lived. For the production of light, at least, such heavy machinery would seem to be unnecessary. The energy required is very small, and if light can be obtained as edi- eiently ns, theoretically, it a pears possible, the apparatus need have but{a very small output. Tgere being a strong probability that the l `\ ‘ 1 ' . ml: l l l l H "" I l ' ' l 1 V 4 J"/Y V\ n_ 9 l ~, . i 5. 5 ‘ --fre F1o.33.-Lsur Kam' ar Incmnnsonnon aoaoss A 'rxucx Connex Baa-Snowmo Nouns. illuminating methods of the future will involve the use of very high potentials, it seems very desirable to perfect a oontrlvnnoe capable of converting the energy ol heat into energy of the requisite form. Nothing to speak of has been done towards this end, for the thought that electricity of some 50,000 or 100,000 volts pressure or more, even if obtained, would be unavailable for practical purposes, has deterred inventors from working in this direction. -- In fig. 31 a plan of connections is shown for converting enr» rents of high into currents of low tension, by means of the dis- ruptive discharge of a condenser. This plan has been used by me frequently for operating a _few incandescent lamps required in the laboratory. Some diiiicultics have been encountered in the arc ol the discharge, which I have been ahle to overcome to a great' extent; be- sides this, and the adjustment necessary for the proper working, no other dimoulties have been met with, and it was easy to operate ordi- nary lamps, and even motors, in this manner” The line being con- nected to the ground, all the wires could be handled with perleotim- punity, no matter how high ,tho pokntial at the terminals of the condenser. In these experiments a high tension induction coil, ope- rated from a battery or from an altemats current machine, was _employed to charge the condenser; but the induction coil might be rep aced by an apparatus of a different kind, capable of giving elec» tncity of such high tension. In this manner, direct or altemnting currents may be converted, and in both cases the current impulses ,may bc otany desired I nency. When the currents charging the condenser are of the sambudirection, and it is desired that the con» _verted currents should also he of one direction, the resistance of the _discharging circuit should, of course, be so chosen that there arena oscillations. _ p ` . ` V In operating devices on the above plnn, I have observed curious phenomena of impedance which are of interest. - For instance, ii a thick copper bar be bent, asindicatéd in fig. 33, and shunted by ordi- nary incandescent lam s, then, by passing the discharge between the knobs, the lamps mayliie brought to incandescence, although they are short-circuited. When a large induction coil is employed it is easy to obtain nodes on the bar, which are rendered evident by the dif- Ierent degree of brilliancy of the lamps, as shown roughly in fig. 33. The nodes are never clearly defined, but there are simply maxima and minima of potentials along the har. This is probably due to the irregularity of the arc between the knobs. In general, when the above-described lan of conversion from high to low tension is used, the behaviour ofp the dismptive discharge may be closely studied. The nodes may also he investigated b meens of an ordinary Cardew voltmeter, which should be well insulixted. Geissler tubes may also be li hted amoss the points of the bent har; in this case, of course, it is lrctter to employ smaller capacities- I have found it practicable to light up in this manner a lamp, and even a Geissler tube. shunted by a short heavy block of metal, and this result seems at first very curious. In fact, the thicker the copper bar in Eg. 33, the better it is for the success of the experiments, as they appear more striking. When lamps with long slender filaments are used, it will be often noted that the filaments are from time to time violently vibrated, the vibration being smallest at the nodal points. This vibration seems to be due to an electrostatic action between the filament and the glass of the bulb. V I _ In tome oi the above sx£\-iments, it is preferable to use special lamps having; straight , ment, s|`,shown'iu fig. 34. When such Fm. 84.-Pnnnounnon or Iurnnancn rs m‘Isc/mnnscnm Lsur. a lamp is used a still more curious phenomenon than those' described ma be observed. The lamp may be placed across the copper bar andlighted, and by using somewhat larger capacities, or, in other words, smaller irequencies, or smaller impulsive impedances, the fila- ment may be brought to any desired degree oi iucaudescence. But when the impedance is increased, a point is reached when compara- tively little current passes throughpthe carbon, and most of it through the rareiied gas ; or erhaps it may be more correct to statethat the current divides nearg evenly through both, in spite of the enormous difference in the resistance, and this would be true 'unless the gas and the filament behave differently. It is then noted that the whole bulb is brilliantly illuminated, and the ends of the leading»iu wires become incandescent, and often throw off sparks in consequence of the violent bombardment, but the carbon tilament remains dark. This is illustrated in fig. 34. Instead of the filament, a single wire extendi ing through the whole bulb may be used, and in this case the pheno- menon would seem to be still more interesting. From the above eyrperimentf it will be evident that,_when ordinary lam s are operated by the converted cdr-rents, those should be pre- ferably taken in which the platinum wires are far apart, and the ire- quencles used should not be too great, else the disoharge’will occur at the ends of the filament or ~in_the base of the lamp between the leading-in wires, and the lamp might then be damaged. " ' ‘ In presenting to yon these results of my investigation on the sub- ject under consideration, I 'have paid on y a passing notice to facts npon which I could have dwelt at length, and among many observa- tions I have selected only those which I thought most likely to interest you. The Held is wide and comfpletely unexplored, and at every step A new truth is gleaned, a novel act observed. How far the results here borne out are capable of practical app‘l.ica¢_ tions will be decided in the future. As regards the production o 'ght, some results already reached are encouraging, and make me eonlident in asserting that the practical solution of the lproblem lies in the direction I have endeavoured to indicate. Bt' I,`whatsver may be the immediate outcome of these experiments I am hopeful that they will only prove a ste to further development towards the ideal and final ‘ perfection. Efha possibilities which are opened by~ modern research are so vast that even ‘the most reserved must feel' sanguine of the future. Eminent scientists consider the problem of utilising one kind ol radiation without the others a rational- one. Inl an apparitus designed for the production of light by conversion from Any* orm of. energy into that -oi light, such 's result can never be reached, for no matter what the 'process of producing the required'

A'UeUs'r.‘ 7, 1891.] vihrntions, be it electrical, chemical, or any ether, it will not he pos- sible to obtain the higher light vibrations without going thronglgdthe lower heativibrations, It is the problem of imparting to L y A certain velocity without passing through all lower velocities. But there is s possibility of obtaining energy not only in the form of light, but motive power and energy of any other form, in some more direct way from the medium. The time will be when this will be accomplished, and the time has come when one may utter such words before an enlightened audience without being considered a visionary, Wo are whirling through endless space with an inconceivable speed, all around useverything is spinning, everything is moving, everywhere is energy. There must be some way of availing ourselves of this energy more directly. Then, with the light obtained from the medium, with the power derived from it, with every form of energy obtained without e ort, from the store for ever inexhnustihla, humanity will advance with giant strides. The mere contemplation of these magniiicent plossibilities expands our minds, strengthens our hopes, and fills our carts with supreme delight. ' -nm rzuannna aovmmr. um ELECTRICAL REVIEW