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

Date: 
Friday, July 17, 1891
Volume: 
3
Pages: 
63-74
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THE ELECTRICAL ENGINEER, JULY 17, 1891. 63 _____ EXPERIMENTS WITH ALTERNATE CURRENTS 0F VERY HIGH FREQUENCY AND THEIR APPLICA- TION T0 METHODS OF ARTIFICIAL ILLUMINA- TION.* nv Nncoca TESLA. There is no subject more captivating, more worthy of study, than nature. To understand this great mechanism, to discover the forces which are active, and the laws which govern them, is the highest aim of the intellect of man. Nature has stored up in the universe infinite energy. The eternal recipient and transmitter of this infinite energy is the ether. The recognition of the existence of ether, and of the functions it performs, is one of the most impor- tant results oi modern scientific research. The mere abandoning of the idea of action at a distance, the assump- tion of a medium prevadingall space and connecting all gross matter, has freed the minds of thinkers of an ever present doubt,and by opening a new horizon-new and unforeseen possibilities-has given fresh interest to phenomena with which we are familiar of old It has been a great step towards the understanding of the forces of nature and their multifold manifestations to our senses. It has been for the enlightened student of physics what the understanding of the mechanism of the firearm or of the steam engine was for the barbarian. Phenomena upon which we used to look as wonders baffling explanation we now see in a different light. The spark of an induction coil, the glow of an incan- descent lamp, the manifestations of the mechanical forces of currents and magnets, are no longer beyond our grasp. Instead of the incomprehensible, as before, their observa- tion suggests now in our minds a simple mechanism, and although as to its precise nature all is still conjecture, yet we know that the truth cannot be much longer hidden, and instinctively we feel that the understanding is dawning upon us. We still admire these beautiful phenomena, these strange forces, but we are helpless no longer ; we can, in a certain measure, explain them, account for them, and we are hopeful of finally succeeding in unravelling the mystery which surrounds them. In how far we can understand the world around us is the ultimate thought of every student of nature. The coarseness of our senses prevents us from recognising the ulterior con- struction of matter, and astronomy, this grandest and most ' Lecture delivered before the American Institute of Electrical Engineers at Columbia College, New York, May 20. positive of natural sciences, can only teach us something that happens, as it were, in our immediate neighbourhood ; of the remoter portions of the boundless universe, with its numberless stars and suns, we know nothing. But far beyond the limit of perception of our senses the spirit still can guide us, and so we may hope that even these unknown worlds-infinitely small and great-may in a measure become known to us. Still, even if this knowledge should reach us, the searching mind will find a barrier, perhaps for ever unsurpassable, to the true recognition of that which seems to be, the mere appearance of which is the only and slender basis of all our philosophy. Of all the forms of nature’s immeasurable, all~pervading energy, which, ever and ever changing and moving, like a soul animates the inert universe, those of electricity and magnetism are perhaps the most fascinating. The effects of gravitation, of heat and light we observe daily, and soon we get accustomed to them, and soon they lose for us the character of the marvellous and wonderful ; but electricity and magnetism, with their singular relationship, with their seemingly dual character, unique among the forces in nature, with their phenomena of attractions, repulsions and rotations, strange manifesta- tions of mysterious agents, stimulate and excite the mind to thought and research. What is electricity 'I and What is magnetism? These questions have been asked again and again. The most able intellccts have ceaselessly wrestled with the problem; still the question has notas yet been fully answered. But while we cannot even to-day state what these singular forces are, yet we have made good headway towards the solution of the problem. We are now confident that electric and magnetic phenomena are attributable to ether, and we are perhaps justified in saying that the effects of static electricity are effects of ether under strain, and those of dynamic electricity and electromagotism effects of ether in motion. But this still leaves the question, as to what electricity and magnetism are, unanswered. First, we naturally enquire, Vffhat is electricity, and is there such a thing as electricity 1 In interpreting electric phenomena, we may speak of electricity or of an electric condition, state or effect. If we speak of electric effects, we must distinguish two such effects, opposite in character and neutralising each other, as observation shows that two such opposite effects exist. This is unavoidable, for in a medium of the properties of ether we cannot possibly exert a strain, or produce a displacement or motion of any kind, without causing in the surrounding medium an equivalent and opposite effect. But if we speak of elec~ tricity, meaning a thing, we must, I think, abandon the idea of two electricities, as the existence of two such things is highly improbable. For how can we imagine that there should he two things, equivalent in amount, alike in their properties, but of opposite character, both clinging to matter, both attracting and completely neutralising each other? Such an assumption, though suggested by many phenomena, though most convenient for explaining them, has little to commend it. If there is such a. thing as electricity, there can be only one such thing, and, excess and want of that one thing, possibly; but more probably its connection determines the positive and negative character. The _old theory of Franklin, though falling short in some respect, is, from a certain point of view, after all, the most plausible one. Still, in spite of this, the theory of the two electricities is generally accepted, as it apparently explains electric phenomena in a more satisfactory manner. But a theory which better explains the facts is not necessarily true. Ingenious 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 acquainting you better with some of the results, which I will describe, to show you the reasoning I have followed, the departures I have made-that I venture to express, in a few words, the views and convictions which have led me to these results. I adhere to the idea that there is a thing which we have been in the habit of calling electricity. The question is, What is that thingl or, What, of all things, the existence of which we know, have we the best reason to call elec-

64 _ THE ELECTRICAL ENGINEER JULY 17 1891 tricity 'I We know that it acts like an incompressible fluid ; that there must be :A constant quantity of it in nature 3 that it can be neither produced nor destroyed ; and, what is more important, the electromagnetic theor of light and all facts observed teach us that electric and etllier phenomena are identical. The idea at once suggests itself, therefore, that electricity might be called ether. In fact, this view has in a certain sense been advanced by Dr. Lodge. His interesting work has been read by ever one, and many have been convinced by his arguments. lilis great ability, and the interesting nature of the subject, keep the reader spellbound; but when the impressions fade, one realises that he has to deal only with ingenious explanations. I must confess that I cannot believe in two electricities, much less in a doubly constituted ether. The puzzlin behaviour of the ether as a solid to waves of light and heat, and as a fluid to the motion ef bodies through it, is certainly explained in the most natural and satisfactory manner by assuming it to be in motion, as Sir William Thomson has suggested; but, regardless of this, there is nothing which would enable us to conclude with certainty that, while a fluid is not capable ef transmitting transverse vibrations of a few hundred or thousand per second, it might not be capable of transmitting such vibrations \vhen they range into hundreds of million millions per second. Nor can anyone prove that there are transverse ether waves emitted from an alternate-current machine, giving a small number of alternations per second ; to such slow disturlr ances, the ether, if at rest, may behave as a true fluid. Returnin to the subject, and bearing in mind that the existence of two electricities is, to say the least, highly improbable, we must remember that we have no evidence of electricity, ner can we hope to get it, unless gross matter is present. Electricity, therefore, cannot be called ether in the broad sense of the term : but nothing would score to stand in the way of calling electricity ether associated with matter, or bound ether; or, in other words, that the so-called static charge of the molecule is other associated in some way with the molecule. Looking at it in that light, we would be justified in saying that electricity is concerned in all molecular actions. New, precisel what the ether surrounding the molecules is, wherein it mbffers from ether in general, can only be conjectured. It cannot differ in density, ether being incompressible ; it must, therefore, be \n\der some strain or in motion, and the latter is the most probable. To under- stand its functions, it would be necessary to have an exact idea of the physical construction of matter, of which, of course, we can only form a mental picture. ( To be umfinued. ) _iii-l

THE ELECTRICAL ENGINEER, JULY 24, 1891. 81 EXPERIMENTS WITH ALTERNATE CURRENTS OF VERY HIGH FREQUENCY AND THEIR APPLICA- TION T0 METHODS OF ARTIFICIAL ILLUMINA- TION.* or Nlicom 'resLA. (Continued from page 64.) But of all the views ou nature, the one which assumes one matter and one force, and a perfect uniformity throughout, is the most scientilic and most likely to be true. An infinitesimal world, with the molecules and their atoms spinning and moving in orbits, in much the same 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 equalisations of ether tensions sets up ether motions or electric currents, and the orbital movements produce the effects of electro and permanent magnetism. About 15 years ago Prof. Rowland demonstrated a most interesting and important fact-namely, thats static charge carried around produces the effects of an electric current. Leaving out of consideration the precise nature of the mechanism which produces the attraction and repulsion of currents, and conceiving the electrostatically charged mole- cules 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 oi rows of directed moving molecule ; we can see that these lines must be closed ; that they must tend to shorten and expand, etc. It likewise explains in a reasonable way the most puzzling phenomenon of all, permanent magnetism, and, in general, has all the beauties of the Ampere 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 1 look upon all electrostatic current and magnetic phenomena as being due to electro- static molecular forces. The preceding remarks I have deemed necessary to a full understanding ofthe subject as it presents itself to my mind. Of all these phenomena the most important to study are the current phenomena, on account of the already extensive and everfgrowing use of currents for industrial purposes. It is now a century since the first practical source of current has been produced, and ever since the phenomena which accompany the flow of currents have been diligently studied, and through the untiring efforts of scientific men Engineers nt (`olnnibia College, New York, May 20.

several layers of fine, well annealed iron wire, which, when wound, is passed through shellac. The armature wires are wound around brass pins, wrapped with silk thread. The diameter of the armature wire in this type of machine should not be more than one-sixth of the thickness of the pole projections, else the local action will be considerable. Fig. 2 represents a larger machine of a different type. The field-magnet of this machine consists of two like parts which either enclose an exciting coil, or else are indepen- dently wound. Each part has 480 pole projections, the at : .- ,=' _ ..=:-» ~~~f..__»~=\f . ,` 1' “gg / A -' 'ire `\ .VA ,/. Li by I *iii l l a 4 i, ‘ t/ \ sa ’ A / ,f~“`£ ~ is' if fr 4 ,v . R , ` I ."\ 4 ' / 13 ’§ i / \ if f i K ._,, . __ I 0 z_...: ~ ~ ~~ .=< ~-4 »=\;='~'- fear’ #ii ' fm. nh &§ “‘”§§;ii::;§i *'“‘“”' :Jem if A . _; r ' __ _.i _ ...; 53», ;_ ¢f.;~»».f¢x~rf-s..' ~ '~¢cx=:wt»s-=»~ mm sewn :wswsw mf -vw Fm. 2, projections of one facing those of thc other. The armature consists of a wheel of hard bronze, carrying the conductors which revolve between the projections of the iiehl magnet. To wind the armatnre condnctors,I have found it most convenient to proceed in the following manner : I construct a ring of hard bronze of the required size. This rinff and the rim of the wheel are provided with the proper inrniber ei pins, and both fastened upon a plate. The armature conductors being wound, the pins are cut off and the ends ni the conductors fastened by two rings which screw to the bronze ring and the rim of the wheel respectively. The whole may then bc taken oil and forms a solid structure. 2 i_ l if. _ .,,;¢.;. sz; fl" -Q igiibx ‘src 1 ag’ ‘ a ? ` Wg’ sv* 1 1° mas “\ 9' ` .'t~- v ' l' 4 ii _ ..__ ~ ‘fi ec-_ 1, _ ,e i 1 ,f a .2 fc Ql H” 9 _ V _-"pf, * ' .ifii-Iibii' in ` 7 \ ' _ , _ .,, f f ,¢._3.~g _, . iw _ , ms, .}~"-»"" ` .32 4;-,' éff” il _ v .- *iw sql. Sf” ,=;,_:_`]3 ,fa g.-'-V3.3 .Xia-: . * 1 ~ 55? *::..' ~ f<< ‘f,,. ‘-'<~-M ¢ _1¥l;J_. .G" ,_ '" i' ' m m ' -e .}5T;:if uv _ " »¢,_;. t,'r_§`~i'¥e?i‘fl¢§a ?-ef ? *gl ` ' ~ - .x.,l‘* lw ~=~ : wrt# s i ;:..\'s¢¢.~-1 ~ "' 7 » »- ,-..s.a,s_.;,f._ » s »- ..» vw E, ,:'f.?' 7<;.»-- --yi-<<-s 'A Q l l ff as msesrr»r~ ' W ““:’5 if of Fio.3. The conductors in such a typo of machine should consist of slicct copper, the thickness of which, of course, depends on the thickness of the pole projections , or clse twisted thin \vires should be employed. Fig, 3 is a smaller machine, in many respects similar to thc former, only here the armature conductors and thc exciting coil are kept stationary, while only a block of wrought iron is rcvolvcd. It would be uselessly lengthening this description were I to dwell more on the details of construction of these machines. Besides,thcy have been described somewhat more elaborately inthe N.Y. Electrical Engineer of March 18, 1891. I deem it well, however, to call the attention of the investi- gator to two things, the importance of which, though self- evident, he is nevertheless apt to underestimate ; namely, to the local action in the conductors, which must be care- fully avoided, and to the clearance, which must be small. I may add, that since it is desirable to use very high peri- pheral speeds, the armature should be of very large diameter in order to avoid impracticable belt speeds. Of the several 'types of these machines \vhich have been constructed by me, I have found that the type illustrated in Fig. 1 caused me the least trouble in construction, as well as in maintenance, and, on the whole, it has been a good experimental machine. In operating an induction coil with very rapidly alter- nating currents, among the first luminous phenomena noticed are naturally those presented by the high-tension 93" . sy ,gif- " it ‘ , "‘ " , -.> . » pf é in. , - . _ fi \'; ` ' " has _.~ »-is .. Flu. 4. discharge. As the number of altcrnations per second is increased, or as-the number being high--the current through the primary is varied, the discharge gradually changes in appearance. It would he difficult to describe the minor changes which occur, and the conditions which bring them about, but one may note five distinct forms of the discharge. First, one may observe a weak, sensitive discharge in the form of a thin, feeble coloured thread, Fig. 4. It always occurs \vhen, the number of alternations per second being high, the current through the primary is very small. In spite of the excessively small current, the rate of change is great, and the diflerence of potential at the terminals of the secondary is therefore considerable, so that the arc is established at great distance; but the quantity of “electricity ” set in motion is insignificant, barely sudicient to maintain a thin, threadlike arc. It is excessively sensitive and may be made so to such a degree that the mere act of breathing near the coil will aifectit, and unless it is perfectly well protected from currents of air, it wriggles around constantly. Nevertheless, it is in this form excessively persistent, and when the terminals are approached to, say, one-third of the striking distance, it can be blown out only with difficulty. This exceptional persistency, \vhen short, s' " 1,- ’ ‘lt Q f - f- ~=' f-» -~wf='f=. .-- . -_ ' _,V , Q ; : q g .., ,._..f , -Q ’ Fila. 5. is largely due to the arc being excessively thin ; presenting, therefore, a very small surface to the blast, Its great sensitiveness, when very long, is probably due to tho motion of the particles of dust suspended in the air. When the current through the primary is increased, the discharge gets broader and stronger, and the effect of the capacity of the coil becomes visible until, finally, under proper conditions, a white flaming arc, Fig, 5, often as thick as one’s finger, and striking across the whole coil, is produced. It develops remarkable heat, and may _be further characterised by the absence of the high note which accompanies the less powerful discharges. To take a_shock from the coil under these conditions would not be advisable, although under different conditions, the potential being much higher, a, shock from the coil may be taken with impunity. (Ta be czmliuueal.)

EXPERIMENTS WITH ALTERNATE CURRENTS 0F VERY HIGH FREQUENCY AND THEIR APPLICA- TION T0 METHODS OF ARTIFICIAL ILLUMINA- -Yr TION . er NIKOLA Testa. (U01lff7L'lLC‘Zlfl'0I7L page 85.) The importance of these elements in an alternate-current circuit is now well known, and, under ordinary conditions, the general rules are applicable. But in an induction coil exceptional conditions prevail. First, the self-induction is of little importance before the arc is established, when it asserts itself; but perhaps never as prominently as in ordinary alternatecurrent circuits, because capacity is dis- tributed all along the coil, and by reason of the fact that the coil usually discharges through very great resistances; hence the currents are exceptionally small. Secondly, the capacity goes on increasing continually as the potential rises, in consequence of absorption which takes place to a considerable extent. Owing to this there exists no critical relationship between these quantities, and ordinary rules would not seem to he applicable. As the potential is increased either in consequence of the increased frequency or of the increased current through the primary, the amount of the energy stored becomes greater and greater, and the capacity gains more and more in importance. Up * Lecture delivered before the American Institute of Electrical Engineers et Columbia College, New York, May 20. to a certain point the capacity is beneficial, but afterftllnl it begins to bc an enormous drawback. It follows }”0l1I this tlnit mn-lx coil gives tho best result with ft SW" frequency nnil priniary current. A very large coil, when operated with currents of very high frequency,l11f\Y "El give :rs much as ,lin. spark. By_adding capacity to ll terminals the condition may be improved, but what the coil really wants is a lower frequency. _ _ Wlnin the flaming discharge occurs, the G0l1dIl|\0I\BBN evidently such that the greatest current is made_to llov through the circuit. These conditions may be attained by varying the frequency within wide limits, _but the higher! frequency at which the flaming arc can still be produced, determines, for a given primary current, the maximum striking distance of the coil. In the flaming discharge the Jelot efl`ect of the capacity is not perceptible 3 the rate al. which the energy is being stored then just equals the rate at which it can be disposed of through the circuit. Thu kind of discliargo is the severest test for a coil; the breali, \\`llL‘l\ it occurs, is of the nature of that in an overcharged Leyden jar. To give a rough approximation I would state that, with an ordinary coil of, say, 10,000 ohms resistance, the most powerful arc would be produced with about 12,000 alternations per second. When the frequency is increased beyond that rate, the potential, of course, rises, but the striking distance may, nevertheless, diminish, paradoxical as it may seem. A1 the potential rises the coil attains more and more the pit perties of a static machine until, finally, one may observe the beautiful phenomenon of the streaming discharge, Fig. 6, which may be produced across the whole length ofthe coil. At that stage streams begin to issue freely from all points and projections. These streams will also be seenl/J pass in abundance in the space between the primary aml the insulating tube. \Vhen the potential is excessively high they will always appear, even if the frequency be low, and even if the primary be surrounded by as much as an inch of wax, hard rubber, glass, or any other insulating substance, This limits greatly the putput of the coil, but I will later show how I have been able to overcome ton considerable extent this disadvantage in the ordinary coil. Besides the potential, the intensity of the streams depends on the frequency; but if the coil be very large they show themselves, no matter how low the frequencies used. For instance, in a very large coil of a resistance ol 67,000 ohms, constructed by me some time ago, they appear with as low as 100 alternations per second and less, the insulation of the secondary being Qin. of ebenite. When very intense they produce a noise similar to that produced by the charging of a Holtz machine, but much more powerful, and they emit a strong smell of ozone. The lower the frequency, the more apt they are to suddenly injure the coil. With excessively high frequencies they may pass freely without producing any other effect thanto heat the insulation slowly and uniformly. The existence of these streams shows the importancecl constructing an expensive coil so as to permit of one'i seeing through the tube surrounding the primary, and the latter should be easily exchangeable: or else the space between the primary and secondary should be completely filled up with insulating material so as to exclude all air. The non-observance of this simple rule in the construction of the commercial coils is responsible for the destruction ol many an expensive coil. At the stage when the streaming discharge occurs, or with somewhat higher frequencies, one may, by approaching the terminals considerably and regulating properly the effect of capacity, produce a veritable spray of small silver white sparks or a bunch of excessively thin silvery threads, Fig. 7, amidst a powerful brush-each spark or thread possibly corresponding to one alternation. This, when produced under proper conditions, is probably the most beautiful discharge, and when an air blast is directed against it, it presents a. singular appearance. The spray ol sparks, when received through the body, causes some inconvenience, whereas, when the discharge simply streams, nothing at all is likely to be felt if large conducting objech are held in the hands to protect them from receiving small burns. If the frequency is still more increased, then the coil

THE ELECTRICAL ENGINEER, JULY 31, 1891. 111 __l_ refuses to give any spark unless at comparatively small distances, and the fifth typical form of discharge may be observed, Fig. 8. The tendency to stream out and dissipate is then so great that when the brush is produced at one terminal no sparking occurs, even if, as I have repeatedly tried, the hand, or any conducting object, is held within the stream; and, what is mere singular, the luminous stream is not at all easily deflected by the approach of 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 is convenient to connect to the terminals of the coil two metallic spheres which may be placed at any desired distance, Fig. 9. Spheres are preferable to plates, as the discharge can be better observed. Byinserting dielectric bodies between the spheres, beautiful discharge phenomena may be observed. If the spheres be quite close and a spark be playing between them, by interposing a thin plate of ebonite between the spheres the spark instantly ceases, and the discharge spreads into an intensely luminous circle several inches in diameter, provided the spheres are sufficiently large. The passage of the streams heats, and after a while softens the rubber so much that two plates may be made to stick together in this manner. lf the spheres are so far apart that no spark occurs, even if they are far beyond the striking distance, by inserting a thick plate of glass, the discharge is instantly induced to pass from the spheres to the glass in the form of luminous streams. It appears almost as though these streams pass through the dielectric. In reality this is not the case, as the streams are due to the molecules of the air which are violently agitated in the space between the oppositely of the air is increased, 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 plate, 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 difference of potential at the terminals of the coil. By approaching a dielectric, the specific inductive capacity of the space between the spheres is increased, pro- ducing the same effect as if the capacity of the spheres were increased. The potential at the terminals may then rise so high that the air space is cracked. The experiment is best performed with a dense glass or mica. Another interesting observation is that a plate of insu- lating material, when the discharge is passing through it, is strongly attracted by either of the spheres-that is, by the nearer one, this being obviously due to the smaller me- chanical ef’l`ect of the bombardment on that side, and perhaps also to the greater electrification. From the behaviour of the dielectrics in these experi- ments we may conclude, that the best insulator for these rapidly alternating currents would be the one possessing the smallest specific inductive capacity, and at the same time one capable of withstanding the greatest differences of potential ; and thus two diametrically opposite ways of securing the required insulation are indicated-namely, to \\se either a perfect vacuum or a gas under great pressure , but the former would be preferable. Unfortunately neither of these two ways is easily carried out in practice. It is especially interesting to note the behaviour of an excessively high vacuum in these experiments. If a test »f -f ,.,_ ' »=' ‘Ts-“W - , "' "VT af. fa J ge, as 1, *15 ( '¥*~'5i" "1 ` ` ' \ . 7 i‘ f ‘ ` "‘ l - ' , f; _ 'f=; *‘*;: A _ fggam hifi -ii I T ' ' ' " "" _> ~ : _ iig ,fo ii izsiii?-g I ';. . 1¥11'f?f1=*" ,L ‘ “-@

1 w 1 r . 112 M .QI.UE.-l°Llt0FEl9i\I;;l3l`lG§!1iEF-PM JULY_§ih%*__~__ effect of alternating currents of very high frequency, I think it necessary to state that, while it is an undeniable fact that they are incomparably less dangerous than currents of low frequencies, yet it should not be thought that they are altogether harmless. What has just been said refers only to currents from an ordinary high-tension induction coil, which currents are necessarily very small; if received directly from a machine or from a secondary of low resistance, they produce more or less powerful effects, and may cause serious injury, especially when used in con- junction with condensers, The streaming discharge of a high-tension induction coil diflers in many respects from that of a powerful static machine. In colour it has neither the violet of the positive, nor the brightness of the negative, static discharge, but lies somewhere between, being, of course, alternatively positive fi f e fa ?= 1* ' ) Xe » . -. 1 1 i ` ~`_,__ -My Fm, 9. and negative. But since the streaming is more powerful when the point or terminal is electrified positively than when electrified negatively, it follows that the point of the brush is more like the positive, and the root more like the negative, static discharge. In the dark, when the brush is very powerful, the root may appear almost white. The wind produced by the escaping streams, though it may he very strong-often indeed to such a degree that it may be felt quite a distance from the coil-is, nevertheless, con sidering the quantity of the discharge smaller than that produced by the positive brush of a static machine, and it effects the flame much less powerfully. From the nature of the phenomenon we can conclude that the higher the frequency, the smaller must, of course, be the wind pro- duced by the streams, and with sufficiently high frequencies no wind at all \vould be produced at the ordinary atnio» spheric pressures. With frequencies obtainable by means of a machine, the mechanical ellect is sufficiently great to , ` ,-.__...»~ \ r , ga g _ <-K it rs" ` ha, 1 A E, ' F Q » _jf_ 'D ,V -»_, ,s ; ' * Fic. 10. revolve, with considerable speed, large pin-wheels, which in the dark present a beautiful appearance owing to the abundance of the streams, Fig. ll. In general, most of the experiments usually performed with a static machine can be performed with an induction coil when operated with very rapidly alternating currents. The effects produced, however, are much more striking, being of incomparably greater power. When a small length of ordin:u‘y cotton-covered \\‘l1'(1, Fig. 12, is attached to one terminal of the coil, thc streams issuing from all points of the \vire may maybe so intense as to produce a consider- able light effect, \Vhen the potentials and frequencies are very high, a wire insulated with guttapercha or rubber and attached to one of the terminals, appears to be covered with a luminous film. A very thin bare \vire when attached to a terminal emits powerful streams and vibrates continually to and fro or spins in a circle, producing a singular effect, Fig. 13. Some of these experiments have been described by me in the Electrical World (New York) of February 21, 1891. Another peculiarity of the rapidly alternating discharge of the induction coil is its radically different behaviour with respect to points and rounded surfaces. If a thick wire, provided with a ball at one end and with a point at the other, be attached to the positive terminal of a static machine, practically all the charge will be lost through the point, on account of the enormously greatn' tension, dependent on the radius of curvature. But if such a wire is attached to one of the terminals of the induction coil, it will be observed that with very high frequencies streams issue from the ball almost as copiously as from the point, Fig. 14. It is hardly conceivable that we could produce such a fa" ' f ` ~ ` 9 ’ ,r-/A{;:f.I~1 ‘ 5% rf ‘_ ,rr lim 7` , sp Q, l \ f ' fi* ll*/W \\ , \.~.,;, » _.. »_,;; Fira, ll. condition to an equal degree in a static machine, for the simple reason, that the tension increases as the square of the density, which in turn is proportional to the radius of curvature; hence, with a steady potential an enormous charge would be required to make streams issue from n polished ball while it is connected with a point. But with an induction coil, the discharge of which alternates with great rapidity, it is different, Here we have to deal with t\vo distinct tendencies, First, there is the tendency to escape which exists in a condition of rest, and which depends on the radius of curvature; second, there is the tendency to dissipate into the surrounding air by condenser action, which depends on the surface. When one of these tendencies is a maximum, the other is at a minimum, At the point the luminous stream is principally due to the air molecules coming bodily in contact with the point; they __ .¢_, " ix? 3 l l it :gi ‘Q ., ,. 1 1\ l , _,:_:;i~_§.-.= -~ . . ______=w_.=é.»; , ._ _._ , " if , , Flu. 12. are attracted and repelled, charged and discharged, and, their atomic charges being thus disturbed, vibrate and emit light waves. At the ball, on the contrary, there is no doubt that the effect is to a great extent produced inductivcly, the air molecules not necessarily coming in contact with the ball, though they undoubtedly do so. To convince ourselves of this we only need to exalt thc condenser* action, for instance, by enveloping the ball, at some distance, by n hetter conductor than the surrounding medium, the con» ductor being, of course, insulated; or else by surrounding it with a better dielectric and approaching an insulated conductor ; in both cases the streams \vill break forth more I-opiously. Also, the larger the ball with agivcn frequency, or the higher the frequency, the more will the ball have the advantage over the point. But, since a certain intensity of action is required to render the streams visible, it is

THE ELECTRICAL ENGINEEIi;ALlQ@l;7, 1891. EXPERIMENTS WITH ALTERNATE CURRENTS OF VERY HIGH FREQUENCY AND THEIR APPLICA- TION 'I`O METHODS OF ARTIFICIAL ILLUMINA- TION.* DY NlK()I,l'\ TESL'/\. - ((,'¢i1Lli'iLzlnl from page 113. ) By preventing completely the exchange of the air molecules, the local heating cflect may be so exalted as tn bring a body to ineandescence, Thus, for instance, if a sniall button, or lirefcrably a very thin wire or l`ll1\lIIOIl\i,lJC enclosed in an nnexhausted globe and connected with the terniinal of the coil, it may be rendered incandescent. The plicnonienon is inadc inncli more interesting by the \'a1ii|l spinning round in a circle of the top of the filament, thus presenting the appearance of a luminous funnel, Fig. IG, which \videns when the potential is increased. When the potential is small the end of the filament may perform irregular motions, suddenly changing from one to the other, or it may describe an ellipse;bnt \Vl]0I\ the potential is very high it always spins in a circle; and so does generally K-J* s~=-»- fi] I f I '_ ‘ ' » 1 ., inf- ii _ V/_ ` .fy J ' ` ”***` * M? 4 Fm. IG. a thin straiglit wire attached freely to the terminal of the coil, 'l`hesc motions are, of course, due to the impact of the molecules, and the irregularity in the distributional the potential, owing to thc roughness and dissyininetry of the wire or filament. With a perfectly symmetriealanrl polished wire such motions would probably not occur. That the motion is not likely to be due to other causes is evident from the fact that it is not of a definite direction, and that in a very l]l,L[lIly-CXIIHIISI-Ufl globe it ceases altogether. The possibility of bringing a body to ineandcscence in an unex~ haustcrl globe, or even when not at all enclosed, would seein to aflbrd a possible way of obtaining light eliects, \vl\ich, in perfecting methods of producing rapidly alter mating potentials, might lic rendered available for useful purposes, In ernploying a commercial coil, the production of very powerful brush eflects is attended with considerable difli- enlties, for when these high frequencies and enormous potentials are used, the best insulation is apt to give way. Usually the coil is insulatcd well enough to stand the strain from convolution to convolution, since two double sill# covered pzrrallined wires will withstand a pressure nl several thousand volts; the dillicnlty lies principally in preventing the breaking tln'ough from the sceondxiry to the primary, which is greatly facilitated by thc streams issuing from the latter. In the coil, of course, the strain is greatest from section to section, but usually in a larger coil there are so many sections that the danger of a sudden giving way is not vci‘y great. Ne difliculty \vill generally be encountered in that direction, and, besides, the liability of injuring the coil internally is very much reduced bv tllu " Lecture delivered before the American Institute of Electrical Engineers at Columbia College, New York, May 20,

T THE ELECTRICAL ENGINEER, AUGUST 7, 1891. 129 fact that the effect most likely to be produced is simply a. gradual heating, which, when far enough advanced, could not fail to be observed, The principal necessity is then to prevent the streams between the primary and the tube, not only on account of the heating and possible injury, but also because the streams may diminish very considerably the potential difference available at the terminals. A few hints as to ho\v this may be accomplished will probably he found useful in most of these experiments \vith thc ordinary induction coil. One of the ways is to wind a short primary, Fig. 17A, so that the difference of potential is not at that length great enough to cause the breaking forth of thc streams through the insulating tube. The length of the primary should be determined by experiment. Both the ends of the coil should be brought out on one end through a plug of insulating material fitting in the tube as illustrated. In such a disposition one terminal of the secondary is attached to a body the surface of which is determined with the greatest care so as to produce the greatest rise in the potential. At the other terminal a powerful brush appears, which may be experimented upon. The above plan necessitates the employment of a primary of comparatively small size, and it is apt to heat when powerful effects are desirable for a certain length of time. In such a case it is better to employ a larger coil, Fig. 1713, and introduce it from one side of the tube, until the streams begin to appear. In this case the nearest terminal of thc secondary may be connected to the primary or to the ground, which is practically the same thing, if the primary is connected directly to the machine. In the case of ground connections it is \vell to determine experimentally But this rapid heating does not need to discourage us in the use of iron cores in connection \vith rapidly alternating currents. I have for a long time been con- vinced that in the industrial distribution by means of transformers, some such plan as the following might be practicable. We may use a comparatively small iron core, subdivided, or perhaps not even subdivided. \Ve may surround this core with a considerable thickness of material which is fireproof and conducts the heat poorly, and on top of that we may place the primary and secondary windings. By using either higher frequencies or greater magnetising forces, we may hy hysteresis and eddy currents heat the iron core so far as to bring it nearly to its maximum permeability, which, as Hopkinson has shown, may be as much as 16 times greater than that at ordinary tempera- tures. If the iron core were perfectly enclosed it would not he deteriorated by the heat, and, if the enclosure of fireproof material would he sufhciently thick, only a limited amount of energy could be radiated in spite of the high temperature. Transformers have been constructed by me on that plan, but for lack of time no thorough tests have as yet been made. Another way of adapting the iron core to rapid alterna- tions, or, generally speaking, reducing the frictional losses, is to produce by continuous magnetisation a How of some- thing like 7,000 or 8,000 lines per square centimetre through the core, and then work with weak magnetising forces and preferably high frequencies around the point of greatest permeability. A higher efiiciency of conversion and greater output are obtainable in this manner. I have also employed this principle in connection with machines in which there is no reversal of polarity. In these types of _- \__ ,. "-~. . .i 1 ' ` Y ` " 1 1; >\ .. si’ ‘p .- \V_ Y; K: ,jg .Q ,> . ' “ _ 2' - _____ -ill il Q23 ""i ’:, 'i"` `i" ‘ F "”i" " " i!di.ili.l...llZi. .... ¢.li:lii:`ifi. `.lI`ff. Fm. l7.\. the frequency \vhich is best suited under the conditions nf the test, Another way of obviatiug the streains, more or less, is to make the primary in sections and supply it from separate well-insulated sources. In many of these experiments, when powerful effects unc wanted for a shnrt time, it is advantageous to use iron cores with the primaries. In such case a very large primary coil may he wound nn-l placed side by side with thc secondary, and, the nearest terminal of the latter being connected to thc primary, a laminated iron core is intro- duced through the primary into the secondary as far as the streams \vill permit. Under these conditions an excessively powerful brush, several inches long, which may be appropriately called “ St. Elmo’s hot fire," may be caused to appear at the other terminal of the secondary, producing striking eficcts. It is a most powerful ozoniser, so powerful, indeed, that only a fe\v minutes are sufficient to fill the whole room \vith the smell of ozone, and it undoubtedly possesses the quality of exciting chemical affinities. For the production of ozone, alternating currents of very high frequency are eminently suited, not only on account ofthe advantages they ofler in thc way of conversion but also because of the fact of the ozonising action of a discharge is dependent on the frequency as \vell as on thc potential, this being undoubtedly confirmed by observation. In these experiments if an iron core is used it should be carefully watched, as it is apt to get excessively hot in an incredibly sho1't time. To give an idea of the rapidity of the heating, I will state that by passing a po\verful current through a coil \vith many turns, the inserting within the siune of a thin iron wire for no more than one second’s time is sufficient to heat the wire to something like 100deg. C. ' Fm. l7n machines, as long as there are only few pole projections, there is no great gain, as the maxima and minima of magnetisation are far from the point of maximum perme- ability; but when the number of the pole projections is very great, the required rate of change may be obtained, without the magnetisation varying so far as to depart greatly from the point of maximum permeability, and the gain is considerable. iygggh E=a,=ss-'i§ is-gs k 2=“fi'§ ,g `\\“\“m?`\\\\\ M 0 O 0 I 'H N ,teas ';:s.'s asia:-Q ,iiaéis !afa===s Q., \\\\ Fm. IS. Thcabove described ;u'i-angcinents refer only to the use of commercial coils as ordinarily constructed. If it is desired to construct a coil for the express purpose of per- forming with it such experiments as I have described, or, generally, rendering it capable of withstanding the greatest possible difference of potential, then a construction as indicated in Fig 18 wiil be found of advantage, The coil , in this case is formed of two independent pa1‘ts which are wound oppositely, the connection bet\veen both being made near the primary. The potential in thc middle being zero,

130 THE ELECTRICAL ENGINEER, AUGUST 7, 1891. there is not much tendency to jump to the primary, and not much insulation is required, In some cases the middle point may, however, be connected to the primary or to the ground. In such a coil the places of greatest difference of potential are far apart and the coil is capable of withstanding an enormous strain. The two parts may be movable so as to allo\v a slight adjustment oi the capacity ciTect. As to the manner of insulating the coil, it will be iound convenient to proceed in the following way: First, the wire should he boiled in paraHln, until all the air is out; then the coil is wound by running the wire through melted pararlin, merely for the purpose of fixing the wire. The coil is then taken off from the spool, immersed in a cylin- drical vessel lilled with pure melted wax, and boiled for a long time until the bubbles cease to appear. The whole is then left to cool down thoroughly, and than the mass is taken out of the vessel and turned up in a lathe, A coil made in this manner and with care is capable of with- standing enormnus potential differences. It may be found convenient to immerse the coil in paral'l‘in oil or some other kind of oil ; it is a most effective way of insulating, principally on account of the perfect exclusion of nir, but it may be found that, after all, IL vessel filled with oil is not a very convenient thing to handle in a laboratory. If an ordinary coil can be dis- mounted, the primary may be taken out of the tube and the latter plugged up on one end, filled with oil, and the primaryreinserted. This affords an excellent insula- tion, and prevents the formation of the streams. Of all the experiments which may be performed with rapidly alternating currents, the most interesting are those which concern the production of n. practical illuminant. It cannot be denied that the present methods, though they were brilliant advances, are very wasteful. Some better methods must be invented, some more periect apparatus devised. Modern research has opened new possibilities for the production of an eflicient source of light, and the attention of all has been turned in the direction indicated by able pioneers. Many have been carried away by the enthusiasm and passion to discover, but in their zeal to reach results, many have been misled. Starting with the idea of producing electromagnetic waves, they turned their attention, perhaps, too much to the study of electromagnetic eflects, and neglected the study of clectrostatie phenomena. Naturally, nearly every iu» vestigator availed himself of an apparatus similar to that used in earlier experiments. But in those forms of apparatus, while the electromagnetic inductive eflects are enormous, the electrostatic effects are excessively small. In the Hertz experiments, for instance, a high»tcnsion induction coil is shertcireuited by an arc, the resistance oi which is very small, the smaller the more capacity is attached to the terminals 3 and the difference of potential at these is enormously diminished. On the other hand, when the discharge is not passing between the terminals, the static effects may be considerable, but only qualitatively so, not quantitatively, since their rise and fall is very sudden, and since their frequency is small. In neither ease, there- fore, are powerful electrostatic effects pereeivable. Similar conditions exist when, as in some interesting experiments of Dr. Lodge, Leyden jars are discharged disruptively. It has been thought-and [ believe asserted-that in such cases most of the energy is radiated into space. In the light oi the experiments which I have described above, it will now not be thought so. I feel safe in asserting that in such cases most of the energy is partly taken up and converted into heat in the are of the discharge and in the conducting and insulating material of the jar, some energy being, of course, given off by electrification of the air ; but the amount of the directly radiated energy is very small. When s. high-'tension induction eeil, operated by currents alternating only 20,000 times a secnnd, has its terminals closed through even zx very small jar, practically all the energy passes through the dielectric of the jar, which is heated, and the electrostatic eifccts manifest themselves outwardly only to a very weak degree. Now thc external circuit of a. Leyden jar-that is, the are and the connections of the coatings-may be looked upon as acircuit generating alternating currents of excessively high frequency and fairly high potential, which is closed through the coatings and the dielectric between them, and from the above it is evident that thc external electrostatic effects must be very small, even if e. recoil circuit be used. These conditions make it appear that with the apparatus usually at hand the observation of powerful electrostatic effects was impos- siblc_ and what experience has been gained in that direction is only due to the great ability of the investigators. But powerful electrostatic effects are a sine que mm of light production on the lines indicated by theory, Electro magnetic effects are primarily llll2t\'i1`ii11i)i0,f0l` the reason that to produce the required effects we would have to pass current impulses through a conductor which, long before the required frequency of the impulses could be reached, would cease to transmit them. Un the other hand, electro- magnetic waves many times longer than those of light, and produciblo by sudden discharges of a condenser, could not bo utilised, it would seem, except we avail ourselves of their eiiect upon conductors as in tho present methods, which are wasteful. We could not affect by means of such waves the static molecular or atomic charges of a gas, cause them to vibrate and to emit light. Long transverse waves cannot, apparently, produce such effects, since excessively small electromagnetic disturbances may pass rcaflily through miles of air. Such dark waves, unless they are of the length ol true light waves, cannot, it would seem, excite luminous radiation in a Geissler 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 electrostatic nature. To 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 the required frequency cannot pass through a. conductor of measurable dimensions, we must work with a gas, and then the production of powerful electrostatic effects becomes an imperative necessity. It has occurred to me, however, that electrostatic effects are in many ways available for the production of light. For instance, we may place a body of some refractory material in a closed, and preferably more or less exhausted, globe, connect it to a source of high, rapidly alternating, potential causing the molecules of the gas to strike it many times a second at enormous 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 a non-striking vacuum, and by employing very high frequencies and potentials transfer sufficient energy from it to other bodies in the vicinity, or in general to thc surroundings, to maintain it at any degree of incandes- cence, or we may, by means of such rapidly alternating high potentials, disturb the ether carried by the molecules of a gas or their static charges, causing them to vibrate and to emit light. But, 0iGCtl`OSt&\.LiC effects being dependent upon the potential and frequency, to produce the most powerful action it is desirable to increase beth as far as practicable. It may be possible to obtain quite fair results by keeping either of these factors small, provided the other is sufli- ciontly great; but we are limited in both directions. My experience demonstrates that \vc cannot go below a certain frequency, for, first, the potential then becomes so great that it is dangerous ; and, secondly, the light production is less ellicient. I have found that, by using the ordinary low frequencies, the physiological cllect of the current required to maintain at a certain degree of brightness a tube 4ft. long, provided at the ends \vith outside and inside condenser coatings, is so powerful that, I think, it might produce serious injury to those not accustomed to such shocks ; whereas, with 20,000 alter-nations per second, the tube may be maintained at the same degree of brightness without any effect being felt. This is due principally to the fact that a much smaller potential is required to produce the same light effect, and also to the higher elliciency in the light production. It is evident that the eiliciency in such cases is tho greater, the higher the frequency, for the quicker the process of charging and disclmrging the molecules, the less energy will be lost in the form of dark radiation. But, uniortunately, wc cannot go beyond a certain frequency on account of the difl'lculty of producing and conveying the eilects. I have stated above that u body enclosed in an unex- hausted 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, duo mostly to the bombardment of the molecules of the gas contained in the bulb. When the bulb is exhausted the heating of the body_is much more rapid, and there is no difficulty whatever in bringing a wire_ or filament to any degree of incandes- ecnco by simply connecting it to one terminal of a coil of the proper dimensions. Thus, if the \vcll-known apparatus of Prof. Crookcs, consisting of a bent platinum wire with vancs mounted over it, Fig. 19, be connected to one terminal of the coil-either one or both ends of the platinum wire being connected-the wi1'e is rendered almost instantly incandescent, and the mica varies are rotated as though a current from a battery were used. A thin carbon filament, or preferably a button of some refractory material, Fig. 20, even if it be a comparatively poor conductor, enclosed in an exhausted globe, may be rendered highly incandescent; and in this manner a simple lamp capable of giving any desired candle-power is provided. The success of lamps of this kind \vonld depend largely on the selection of the light-giving bodies contained within the bulb. Since, under the conditions described, refractory bodies-which are very poor conductors and capable of withstanding for a long time excessively high degrees of temperature-may be used, such illuminating devices may bc rendered successful. It might be thought at Hrst that if the bulb containing thc filament or button of refractory material, be perfectly \vcll exhausted-that is, as far as it can bc done by tho 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 contrary, the better the vacuum the more easily the bodies are brought to incandescence. This result is interesting for many reasons. ,._ I ‘R :pi ~ _ -- ' i i ly) ’,_ T " 4 E/ s» ' ` - Qi," ' Q ' ;.,,,s e r J- 'éhr ' 4_@ / Fin. lf). Flo. QU. At the outset of this work, the idea presented itself to me 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 be rendered incandescent by mere con' denser action. Obviously, to reach this result, enormous potential differences and very high frequencies are required, as is evident froma simple calculation. But such a lamp \vonld possess a vast advantage over an ordinary incandescent lamp in regard to efficiency. It is \vcll known that the efficiency of a lamp is to some extent a function of the degree of incandescence, and that, could we but work a filament at many times higher degrees of incandescence, the efficiency would be much greater. In an ordinary lamp this is impracticable on account of the destruction of the filament, and it has been determined by experience ho\v far it is advisable to push the incan- desccnce. It is impossible to tell ho\v much higher efiiciency could be obtained if the filament could with- stand indefinitely, as the investigation to this end obviously cannot be carried beyond a certain stage ; but there are reasons for believing that it \vonld be very considerably higher. An improvement might be made in the ordinary lamp by employing a short and thick carbon ; but then the leading-in wires \vonld have to be thick, and, besides, there are many other considerations which render such a modification entirely impracticablc. But in a lamp as above described the leading-in \Vll'CS may be very small, the incandescent refractory material may be in the shape of blocks offering a. very small radiating surface, so that less energy \vonld be required to keep them at the desired incandescenoe; and, in addition to this, the refractory material need not be carbon, but may be manufactured from mixtures of oxides, for instance, \vith carbon or other material, or may be selected from bodies which are practi- cally non-conductors, and capable of withstanding enormous degrees of temperature. All this would point to the possibility of obtaining a much higher efficiency with such a lamp than is obtainable in ordinary lamps. In my experience it has been demon- strated that thc blocks are brought to high degrees of incandescence with much lower potentials than those determined by calculation, and the blocks may be set at greater distances from each other. \Ve may freely assume, and it is probable, that the molecular bombardment is an important element in the heating, even if the globe be exhausted \vith the utmost care as I have done ; for although the number of the molecules is, comparatively speaking, insignificant, yet on account of the mean free path being very great, there are fewer collisions, and the molecules may reach much higher speeds, so that the heating effect due to this cause may be considerable, as in the Crookes experiments \vith radiant matter. But it is likewise possible that we have to deal here with an increased facility of losing the charge in very high vacuum, when the potential is rapidly alternating, in \vhich case most of the heating would be directly due to thc ` ' " `f=:?;if‘f=~; ‘ . ,ar _._ /” »fs .» is K ‘» Q E 3. go, i "’ ‘N 2 ix or-*off is . tf;:c+f‘§ ,_ <.-w .sg-_p 15, , ' ,. ¢~ 1.5 1... NS ~' " 7% f,i,;‘,“€.fi ,z-~. ~ I ». 1 ~ if 1 3 J. -- ¢~_ >.; ,;v f `::3:L' ml: ‘r‘ 2 ~ ' »i _:T ;:` , c 1. »il' r» »\~ .. we = -'Q 'ri “‘ . `, ` IrgE’{f'_ li' "i sy? . l1‘§ . ,_ . f. _._ . W _ , <=.»>;.v.x sd Fic. 21. Fin. 22. surging of the charges in the heated bodies. Or elsc the observed fact maybe largely attributable to the effect of the points \VlllCl1 I have mentioned above, in consequence of which the blocks or filaments contained in the vacuum are equivalent to condonsers of many times greater surface than that calculated from their geometrical dimensions. Scientific men still differ in opinion as to whether a charge should, or should not, be lost in a perfect vacuum, or, in other \vords, whether ether is, or is not, a conductor. If the former were the case, then a thin filament cncloscd in a perfectly exhausted globe, and connected to a source of enormous, steady potential, would be brought to incan- dcsccncc. Various forms of lamps on the abovedescribed principle, \vith the refractory bodies in the form of filaments, Fig. 21, or blocks, Fig. 22, have been constructed and operated by mc, and investigations are being carried on in this line. There is no difiiculty in reaching such high degrees of incandesccncc that ordinary carbon is to all appearance melted and volatilised. lf the vacuum could be made absolutely perfect, such a lamp, although inoperative with appa1‘atns ordinarily used, would, if operated with currents of the required character, afford an illuiniuant which would never be destroyed, and which would be far more efficient than an ordinary incandescent lamp, This pcrfcction can, of course, never be reached, and a very slow destruction and gradual diminution of the size always occurs, as in incandescent lamps; but there is no possibility of a sudden and premature disabling which occurs in the latter by the breaking of the filament, especially when the incandescent bodies are in the shape of blocks. (To be continued.)

THE ELECTRICAL ENGINEER, AUGUST 14, 1891. 159 EXPERIMENTS WITH ALTERNATE CURRENTS OF VERY HIGH FREQUENCY AND THEIR APPLICA- TION T0 METHODS OF ARTIFICIAL ILLUIVIINA- Tl0N.* nv NIKOLA 'ri<1sLA. ((7ozilinzm¢Z]'rozn page ISU.) With these rapidly alternating potentials there is, ho\v- ever, no necessity of enclosing two blocks in a globe, but a single block, as in Fig. 20, or filament, Fig. 23, may be used. The potential in this case must of course be higher, but it is easily obtainable, and besides it is not necessarily dangerous. The facility with which the button or filament in such a lamp is brought to incandescence, other things being equal, M’ I Wg"-s ‘~‘ sie; ’ 11. i "'_; ' . '_ ‘i1i;,;.?=f.;.' ;_ l ,ar ; `='==“ffi if ' it `" +4 -.z_§ Q ,V 9% Fm. 23. depends on the size of the globe. If a perfect vacuum could be obtained, the size of the globe would not be of importance, for then the heating would be 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 ` Lecture delivered before the American Institute of Electrical Hngincerfi at Columbia College, New York, May 20. the globe, and although the exhaustion may be carried to the highest degree, still the space inside of the bulb must be considered as conducting WhCl\ such high potentials are used, and I assume that in estimating the energy that may be given off 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. \Vhen the alternations are very low there is no doubt that a considerable portion of the energy is given off by the electrification of the surrounding air. In order to study this subject better, I carried on some experiments with excessively high potentials and lo\v frequencies. I then observed that \vhen the hand is approached to the bulb-the filament being connected \vith one terminal of the coil-a powerful vibration is felt, being due to the attraction and repulsion of the molecules of the air which are electrihed by induction through the glass. In some cases where the action is very intense I have been able to hear a sound, which must be due to the same cause. When tho alternations are low, one is apt to get an excessively powerful shock from the bulb. In general, \vhen one attaches bulbs or objects of some size to the ter< minals of the coil, one should look out for the rise of potential, for it may happen that by merely connecting a bulb or plate to the terminal, the potential may rise to many times its original value. When lamps are attached to the terminals, as illustrated in Fig. 24, then the capacity of the bulbs should be such as to give the maximum rise of poten- tial under the existing conditions. In this manne1‘ one may obtain the required potential \vith fewer turns of wire. The life of such lamps as described above depends, of course, largely on the degree of exhaustion, but to some extent also on the shape of the block of refractory » raw. _ -. ,`- £11 'Ml fx *~. ef-.f-¢:.i§Yfi;>Ps“5¢" ._ `\ - V ~ IQ; _ (v_ gf , Q _ v ._. >1; ga T g i g = = -f ~_§ ”i? :”' ' ~“-1”--.__ r' ;???ii?i _ ¢__s, _ _, _ _V /__ ~;-s , Fm. '24, material. Theoretically it \V0llld seem that a small sphere of carbon enclosed in a sphere of glass would not suffer deterioration from molecular bombardment, for, the matter in the globe being radiant, the molecules would move in straight lines, and would seldom strike the sphere obliquely. An interesting thought in connection \vith such a lamp is, that in it “ electricity ” and electrical energy apparently must move in the same lines. The use of alternating currents of very high frequency makes it possible to transfer, by electrostatic or electro- magnetic induction through the glass of a lamp, sufficient energy to keep a filament at incandescence and so do away with the leading-in wires. Such lamps have been proposed, but for want of proper apparatus they have not been successfully operated. Many forms of lamps on this principle, \vith 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 effected by electrostatic induction, the potentials used are, of course, very high with frequencies obtainable from a machine. For instance, with a condenser surface of 40 centimetres square, which is not impracticably large, and with glass of good quality I mm. thick, using currents alternating 20,000 times a second, the potential required is approximately 9,000 volts. This may seem large, but since each lamp maybe included in the secondary of a transformer of very small dimensions, it would not be inconvenient, and, moreover, it would not produce fatal injury. The transformers would all be preferably in series. The regulation would offer no difliculties, as with currents

`l§QfY EYLEC'1‘RICALHF.NGINEER, AUGUSTili1;§91. _ of such frequencies it is very easy to maintain a constant, current. In the accompanying engravings some of the types of lamps of this kind are shown. Fig. 25 is such a lamp with a broken filament, and Fig. 26A and Fig. 26|i one with a single outside and inside coating and a single filament. l have also made lamps with two outside and inside coatings, and a continuous loop connecting tho latter. Such lamps have been operated by me with current impulses of the enormous frequencies obtainable by the disruptive discharge of condenscrs. The disruptive discharge of a condenser is especially suited for operating such lamps-with no outward electrical eonnections-by means of electromagnetic induction, the electromagnetic inductive eilucts being excessively high; necting one terminal of the lamp to one terminal of the source, and the other to an insulated body of the required size. In all cases the insulated body serves to give off the energy into the surrounding; space, and is equivalent to a return wirc, Obviously, in the two lastfnamed cases, instead of connecting the wires to an insulated body, connections may be made to the ground. - The experiments which \vill prove most suggestive and ol most interest to the investigator are propably those per- formed with exhausted tubes. As might be anticipated, a source of such rapidly alternating potentials is capable oi exciting the tubes at a considerable distance, and the light effects produced are remarkable, During my investigations in this line I endeavoured to excite tubes, devoid of any electrodes, by electromagnetic induction, making the tube the secondary of the induction _fx 5 device, and iassiu threuffh the rimar the discharffes of / \ ,_ _l if-i n P Y x: ,ff =,\ a Leyden ]ar. These tubes were made of many shapes, 'f 0 , "Q and I was able to obtain luminous ell'ects which I then dy ','f‘£{E§ _» thought were due wholly to electromagnetic induction. _ Q "_ But on carefully investigating the phenomena I found that ` _; the effects produced were more of an electrostatic nature, .ir__~"l'i ' if It may be attributed to this circumstance that this mode ul '= exciting tubes is very wasteful-namely, thepriinary circuit if being closed, the potential, and consequently thc electre< Fm. 25 , static inductive eflect is much diminished. _fr //"`~ 5; " /' gf Bi ‘Q \ I yi . 3 J ,= / i' I 'I `- ' he , 3 ! ` . i E Jiffy' i g._ ‘J _ i Fm. Qtin. Fuz. 2G.\. Fm' QS' and I have been able to produce the desired incandesccnce with only a fe\v short turns of wire. Incandcscence may also be produced in this manner in a simple closed filament. Leaving, now, out of consideration the practicability oi such lamps, I \vould only say that they possess a beautiful and desirable feature-namely, that they can be rendered at will mo1'e or less brilliant, simply by altering the relative position oi the outside and inside condenser coatings, or inducing and induced circuits. i l When an induction coil, operated as above described, is used, there is no doubt that the tubes are excited by elcrtni- static induction, and that electromagnetic induction has little, if anything, to do with the phenomena. This is evident from many experiments, F01‘l!lSi,l\.llC(!,ll'I\ tube be taken in one hand, the observer being near the coil, it is brilliantlylighted and remains so in no matter whatpositilm it is held relatively to the Dl)SC\`\'Cl'iS body Were the action electromagnetic, the tube could not be lighted when the ` observer’s body is interposed between it and the coil, or , at least its luminosity should be considerably diminished, _ 1 When the tube is held exactly over the centre of the coil- * the latter being wound in sections and the primary placed -, , .V "'_ ,`,% ' “J” " J( _ w/f f x “ _ _:_ _ 1. » $\,ii?§,,;§,‘ ; 1 fs;~ .i;;-as) ~__ if' Fur. Ull- .5.;1;:3=" 55' ' 1139 symmetrically to the secondary-it may remain ctnnplclcly F 27 dark, whereas it is rendered intensely luminous by moving IH. . I A When a lamp is lighted by connecting it to one terminal only of the source, this may be facilitated by providing the globe \vith an outside eondcnaer coating, which serves at the same time as a rel'lector, and connecting this to an insulated body of some size. Lamps of this kind are illns» trated in Fig. 27 and Fig. 28. Fig. 29 shows the plan of connections. The brilliuncy of the lamp may in this case be regulated \vithin wide limits by varying the size of the insulated metal plate to which the coating is connected. It is likewise practicable to light with one leading wire lamps, such as illustrated in Fig. 21 and Fig. 22, by con- it slightly to the right or left from the centre of the coil. It does not light because in the middle both halves of the coil ncutralise each other, and ~thc electric potential is zero. If the action \vere electromagnetic, the tube should light best in the plane through the centre of the coil, since the electromagnetic etlect thc1'e should be a maximum. When an are is established between the terminals, the tubes and lamps in the vicinity of the coil go out, but light up again when the arc is broken, on account of the rise of potential. Yet the electromagnetic effect should be practically the same in both cases. By placing a tube at seine distance from the coil, and nearer to one terminiil#preferably nt zu point on the axis

? of the coil-one may light it by touching the remote terminal \vith an insulated body of seine size or with the hand, thereby raising the potential at that terminal nearer to the tube. If the tube is shifted nearer to the coil so that it is lighted by the action of the nearer terminal, it may be made to go out by holding, on an insulated support, the end of a wire connected to the remote terminal, in the vicinity of the nearer terminal, by this means counteracting the action of the latter upon the tube, These etlccts are evidently electrostatic. Likewise, when a tube is placed at a considerable distance from the coil, the observer may, standing upon an insulated support, between coil and tube, light the latter by approaching the hand to it; or he may even render it luminous by simply stepping between it and the coil. This would be impossible with electromagnetic induction, for the body of the observer would act as a screen. When the coil is energised by excessively weak currents, the experimentermay, by touching one terminal of the coil with the tube, extinguish the latter, and may again light it by bringing it out of contact \vith the terminal and allowing a small are to 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 \vhen the are is broken, because the electrostatic inductive eilect alone is too weak, though the potential may be much higher; but when the are is cstablished, the electrification of the end of tho tube is much greater, and it consequently lights. If a tube is lighted by holding it near to the coil, and in the hand which is remote, by grasping the tube anywhere \\'ith the other hand, the part betwccn the hands is rendered dark, and the singular effect of wiping out the light of the tube may be produced by passing the hand quickly along the tube and at the same time \Vll¢l1(ll'i\Wlllg it gently from the coil, judging properly the distance so tbnt the tube remains dark l\fl,Cl'\\'ill‘(lS. If the primary coil is placed sidcwisc. ns i|\ Fig. 1715 for instance, and an exhausted tube be introduced from the other side in the hollow space, the tube is lighted most in- tensely because of the increased condenser action, and in this position the striu: are most sharply defined. In all these experiments described, and in many others, the action is clearly electrostatic. The eilccts of screening also indicate the electrostatic nature of thc phenomena and show something of the nature of electrification through the air. For instance, if a tubc bc placed in the direction of the axis of the coil, and an insulated metal plate be interposed, the tube will generally increase in brilliancy, or if it bo too far from the coil to light, it may even he rendered luminous by intcrposing an insulated metal platc. The magnitude of the effects depends to some extent on the size of tho plate. Hut if the metal plate be connected hy a wirc to the ground, its interposition will always make the tube go out, even if it be very near the coil. In general, the interposition of a body between the coil and tube, increases or diminishes the brilliancy of the tube, or its facility to light up, according to whether it increases or diminishes the electrification. When experi- menting \vith an insulated plate, the plate should not be taken too large, else it will generally produce a weakening cllcct by reason of its great facility for giving off energy to the surroundings. If a tube be lighted at some distance from the coil, and a plate of hard rubber or other insulating substance be inter- posed, the tube may be made to go out. The interposition of the dielectric in this case only slightly increases the inductive eH`cct, but diminishes considerably the electrifica- tion through the air. In all the cases, then, \vhen \ve excite luminosity in exhausted tubes by means of such a coil, the eIl`ect is due to the rapidly alternating electrostatic potential 3 and, further- more, it must be attributed to the harmonic alternation pro- duced directly by the machine, and not to any superimposed vibration which might be thought to exist. Such super- imposed vibrations arc impossible when we work with an alternatecurrent machine. If a spring bc gradually tightened and released, it docs not perform independent vibrations 3 for this a sudden rclcasc is necessary. So with the alter- nate currents from a dynamo machine z the medium is harmonically strained and released, this giving x'ise to only one kind of waves ; a sudden contact or break, or a sudden giving \vay of the dielectric, as in the disruptive discharge of a Leyden jar, are essential for the production of super- imposed waves, In all the last described experiments, tribes devoid of any electrodes may be used, and there is no difliculty in producing by their means sufiicient light to read by. The light effect is, however, considerably increased by the use of phosphorescent bodies such as yttria, uranium, glass, etc. A difficulty will be found when the phosphorescent mate- rial is used, ior with these powerful ellects it is carried gradually away, and it is preferable to use material in the form of a solid. Instead of depending on induction at a distance to li ht the tube, the same may be provided \vith an external- and, if desired, also with an internal-condenser coating, and it may then be suspended anywhere in the room from a conductor connected to one terminal of the coil, and in this manner a soft illumination may be provided. ( To be continued.)

THE ELECTRICAL ENGINEER, AUGUST 21, 1891. 177 -1. ..i... EXPERIIVIENTS WITH ALTERNATE CURRENTS OF VERY HIGH FREQUENCY AND THEIR APPLICA- TION T0 METHODS OF ARTIFICIAL ILLUMINA- 'l`ION.* HY NIKOLA 'l'l4lSLA. (Cu/iclznlcilfrom page IGI). The ideal \vay of lighting a hall or room, would, how- ever, be to produce such a condition in it that an illumi~ nating device could be moved and put anywhere, and that it is lighted, no matter where it is put, and _,i___l 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 alarge conducting object is fastened on an insulating support, and the hand approached to it, a vibration, due to the rythmical motion oi the air molecules, is felt, and 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 of 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 capable of practical application the future will tell. It might be thought that electrostatic effects are unsuited for such action at a distance. Electro- magnetic inductive effects, if available for the production of light, might be thought better suited. It is true the elec- trostatic effects diminish nearly with the cube of the distance from the coil, whereas the electromagnetic inductive eiiects diminish simply with the distance. But when we establish an electrostatic field of force, the condition is very different, for then, instead of the differential edect of both the terminals, we get their cojoint effect. Besides, I would alternating electro- exhausted tube for energy, whereas, in the conductor tends being reflected with is diflicult to excite call attention to the fact, that in an static field, a conductor, such as an instance, tends to take up most of the an an electromagnetic alternating field to take up the least energy, the waves but little loss. This is one reason why it an exhausted tube, at a distance, by electromagnetic induc- tion. I have wound coils of very large diameter and of many turns of wire, and connected a Geissler tube to the ends ofthe coil with the object of exciting the tube at a distance ; but even with the powerful inductive effects pro- ducible by Leyden jar discharges, the tube could not be excited unless at a very small distance, although some judgment was used as to the dimensions of the coil. Ihave also found that even the most powerful Leyden jar dis- charges are capable of exciting only feeble luminous effects in a closed exhausted tube, and even these effects upon thorough examination I have been forced to consider of an electrostatic nature. ~._,, ,. ‘ ...~\?.< .?<:“"f@:~:~ s r ,i i gs J: .. QPZ?&s:¥.‘sij;c:3`.~_;' ;__ L;.f.°¢3§§>,;;_;i':'»g, ii- aa,-3-i,.;. ,qv .i ~‘i' ¢,:~s¢ =2 in ' f . ~ .5 ,»;¢,1,»s;»a ef ‘efesmscez-¢e~=~e'= ,, ~»1~= 4 ; - ~ \. ~ tw'-':§:¢» _w:>;-fc~ >1¢.t"; E€£'%a»»'::5~&¢": 11~.~§1fN>. of -"rs-.~ .s #1 ~ , ., »»»._.,..,..§ M ,o ,t,.., as s...»¢ ., as , _..,»,~§aq§~,s_ __ _.i I _, .<=§\:€F$¥-133% '¢"‘1 `| ll' ""*<¥ '“‘._f* ` ' -*FY - in K \ ;-;|;i},1|| , -"' f » ‘ ~ r' hgh, .1 ‘» :FV A ' ' ‘-i¢.:v.€ . , nf . .;¢,'~,.~i w as . . . , s 1| Ld \ aiiiih iililii ‘ p;|p.gI., g In |i:,V, . !' , d " \“»iJ f y' iii I “<., i =-` ,» _ " .ill . '\ "` ~i 5' .. ._ '1~\,i, ’?‘ "cw-_ fs' l l. Y "~ ¢ v{¢Q `9“"i M ~',,i f-_ .» Phi? ‘S ‘f%j,$tLi~‘ “ " :a;}3.§i‘1“:N”‘1-39" " "‘_’;f » , iff' ._ _ . e},‘_ > ,L '-‘ \<_` -“‘~-` " * ‘ Flu. 30. without being electrically connected to anything. I have been able to produce such a condition by creating in thc P00111 a powerful, rapidly alternating clcctrostatic Held, For this purpose I suspend a shcct of metal a distance from the ceiling on insulating cords and connect it to one terminal of the induction coil, the other terminal liciug preferably connected to tho ground. Or else I sns~ pend two sheets as illustrated in Fig. 30, each sheet being connected with one of the terminals of the coil, and their size being carefully determined. An exhausted tube may then be carried in the hand anywhere bet\vcen the sheets or placed anywhere, even u certain distance beyond them ; it remains always luminuous. I|\ such an electrostatic field interesting phenomena may he observed, especially if the nltcrnations are kept low and the potentials excessively high. luaddition to the luminous ` Lccturo delivered before the American Institute of Electrical lingiuoors ut fiolumbiu (`ollcgc, New York, May 20. How, then, can we hope to produce the required effects at a distance by means of electromagnetic action, when even in the closest proximity to the source of disturbance, under the most advantageous conditions, we can excite but faint luminosity? It is truo that when acting ut a distance wc have thc resonance to help us out. \Vc can connect an exhausted tube, or whatever the illuminating device may be, with an insulated system of the proper capacity, and so it may be possible to increase the efiect qualitatively, and only qualitatively, for we would not get more energy through the device. So we may by resonance eflect obtain the required E.M.F. in an exhausted tube, and excite faint luminous effects, but we cannot get enough energy _to render the light practically available, and a simplecalclilation,based on experimental results, shows that even if all the energy which a tube would receive at a certain distance _from the source should be wholly converted into light, it \vould hardly satisfy tho practical l‘C(l\llI'Bm€l\tS- IIGHCG Ulm

|78 ’I‘lffIC ELECTRICAL ENGINEER, AUGUST 21, 1891. necessity of directing, by means of a conducting circuit, the energy to the place of transformation. But in so doing we cannot very sensibly depart from present methods, and all we could do would be to improve the apparatus. From these considerations it would seem that if this ideal way of lighting is to be rendered practicableit will be only by the use of electrostatic effects. In such a case the most powerful electrostatic inductive effects are needed; the apparatus employed must, therefore, he capable of pros ducing high electrostatic potentials changing in value with extreme rapidity. High frequencies are especially wanted, for practical considerations make it desirable to keep down the potential. By the employment of machines, or, generally speaking, of any mechanical apparatus, but low frequencies can be reached; recourse must, therefore, be had to some other means. Tho discharge of a condenser affords us a means of obtaining frequencies by far higher than are obtainable mechanically, and I have accordingly employed condensers in the experiments to the above end. When the terminals of a high tension induction coil, Fig. 31, are connected to a Leyden jar, and thc latter is discharging disruptively into a circuit, we may look upon the arc playing between the knobs as being a source of alternating, or generally speaking, undulating currents, and then we have to deal with the familiar system of a generator of such currents, a circuit connected to it, and a condenser bridging the circuit. The condenserin such case is a veritable transformer, and since the frequency is exces- sive, almost any ratio in the strength of the currents in both the branches may be obtained. In reality, the analogy is not quite complete, for in the disruptive discharge we have most generally a fundamental instantaneous variation of comparatively low frequency, and a superimposed harmonic vibration, and the laws governing the flow of currents are not the same for beth. Flo. 31. In converting in this manner, the ratio of conversion should not be too great, for the loss in the arc between the knobs increases with the square of the current, and if the jar be discharged through very thick and short conductors, with the view of obtaining a very rapid oscillation, a very considerable portion of the energy stored is lost. On the other hand, too small ratios are not practicable for many obvious reasons. As the converted currents flow in a practically closed circuit, the electrostatic effects are necessarily small, and I therefore convert them into currents or effects of the required character. I have effected such conversions in several ways. The preferred plan of connections is illus- tratcd in Fig. 32. The manner of operating renders it easy to obtain by means of a small and inexpensive apparatus enormous differences of potential which have been usually obtained by means of large and expensive coils. For this it is only necessary to take 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 need have comparatively but very few turns. By properly adjusting the elements remarkable results may be secured. In 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 not as yet prepared to dwell upon my experiences in this direction. I believe that the disruptive discharge of a condenser will play an important part in the future, for it offers vast possi- bilities, not only in the way of producing light in a more ,___ __ . eflicient manner and in the line indicated by theory, hid also in many other respects. _ , For years the efforts of inventors have been directed towards obtaining electrical energy from heat by means of the thermopile. It might seem invidious to remark that but few kno\v what is the real trouble with the thermopile. It is not the inefficiency or small output-though ‘these are great drawbacks-but the fact that the thermopxle has its phylloxerafthat is, that by constant use it is deteriorated, which has thus far prevented its introduction on an indus# trial 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. \Ve have been used to look upon an electrostatic machine as a plaything, and somehow we couple with it the idca of the inefficient and impracticil. But now we must think differently, for new we know that everywhere we have to deal with the same forces, and that it is a mere question of inventing proper methods or apparatus for rendering them available. ‘ In the present systems of electrical distribution, thu employment of the i1‘on with its wonderful magnetic properties allows us to reduce considerably thc size of the apparatus ; but, in spite of this, it is still very cumbersome. The more we progress in the study of electric and magnetic phenomena, the more we become convinced that the prcsonf methods will be shorfrlivcd. For the production of light, at least, such heavy machinery would seem to be unneces- sary. The energy required is very small, and if light can be obtained as efficiently as, theoretically, it appears possible, the apparatus need have but a very small output. There being a. strong probability that the illuminating methods of the future will involve the use of very high potentials, if seems very desirable to perfect a contrivance capable ol converting the energy of heat into ene1‘gy of the requisite form. Nothing to speak of has been done to\vards this / ~-~~_ / . ; Fic. 32. end, for the thought that electricity of some 50,000 or 100,000 volts pressure or more, even if obtained, would he unavailable for practical purposes, has deterred inventors from working in this direction. In Fig. 31 a plan of connections is sho\vn for converting currents of high, into currents of low, tension by means of the disruptive discharge of a condenser. This plan has been used by me frequently for operating a fe\v incan~ descent lamps required in the laboratory. Some difliculties have been encountered in the arc of the discharge which l have been able to overcome to a great extent; besides this, and the adjustment necessary for the proper \vorking,no other difficulties have been met with, and it \vas easy In operate ordinary lamps, and even motors, in this manner. The line being connected to the ground, all the wires could be handled with perfect impunity, no matter ho\v high the potential at the terminals of the condenser. In these experiments a high-tension induction coil, operated from s battery or from an alternatecurrent machine, was employed to charge the condenser; but the induction coil might be repla‘ed by an apparatus of a different kind, capable of giving el wtricity of such high tension. In this manner, direct or alternating currents may be converted, and in both cases the currentimpulses may be of any desired frequency, When the currents charging the con- denser are of the same di1'ection, and it is desired that the converted currents should also be of one direction, the resistance of the discharging circuit should, of course, he so chosen that there are no oscillations. In operating devices on the above plan, I have observed curious phenomena of impedance ‘which are of interest. For instance, if a thick copper bar be bent, as indicated in

THE ELECTRICAL ENGINEER, AUGUST 21, 1891. 179 Fig. 33, and shunted by ordinary incandescent lamps, then, by passing the discharge between the knobs, the lamps may be brought to incandescence although they are short- cireuited. When a large induction coil is employed it is easy to obtain nodes on the bar, which are rendered evident by the different 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 bar. This is probably due to the irregularity of the arc between the knobs. In general when thc above described plan of conversion from high to low tension is used, the behaviour of the disruptive discharge may be closely studied. The nodes may also be investi- gated by means of an ordinary Cardew voltmeter which should be well insulated. Geissler tubes may also be lighted across the points of the bent bar, in this case, of course, it is better to employ smaller capacities. I have found it prac- ticable to light up in this manner a lamp, and even a Geissler tube, shuutcd by a short heavy block of metal, and this result seems at first very curious. In fact, the thicker the copper bar in Fig. 33, thc better it is for the success of the experiments, as they appear more striking. \VlJ.61\ 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. I _ . \ \ .-’ A + 'rf 1 /< ; If .»-M I \ K' PT* K M I I _ . ljiil l ` ..‘;f2f.-af ~‘ ~ ~ ill ,,,, \ . l lil li `“@illi""ii » ii. 4 .t ___.; WI Ip _.... i"1l|l|\li- t" ‘ff ""‘~<-»;2"?» < " -" ,Iris -Q., .C :~,;:, ff-»x=2'F” - ~ g Q _ a.,--f ,4 W: , ` e ' -?i€??§€ 5 Q »-1 H _ * .ss ll... _., sg, J 'l\I|1" Fm. 33. In some of the above experiments it is preferable to use special lamps having a straight filament, as shown in Fig 34. When such a lamp is used a still more curious phenomenon than those described may be observed. The lamp may be placed across the copper bar and lighted, and by using somewhat larger capacities, or, in other words, smaller frequencies, or smaller impulsive impedancies, the hlamcnt may be brought to any desired degree of incan- desccnce. But when the impedance is increased a point is reached when comparatively little current passes through the carbon, and most of it through the rarified gas; or perhaps it may be more correct to state that the current divides nearly evenly through both, in spite of the enor- mous diflerence in the resistance, and this \vould 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-in wires become incandescent and often throw ofl' sparks in consequence of the violent bombardment, but the carbon filament remains dark. This is illustrated in Fig. 34. Instead of the filament a single wire extending through the the whole bulb may be used, and in this case the phenomenon would seem to bo still more interesting. From the above experiment it will be evident that when ordinary lamps are operated by the converted currents, those should be preferably taken in which the platinum wires are far apart, and the frequencies used should not be too great, else the discharge 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 you these results of my investigation on the subject under consideration, I have paid only a passing notice to facts upon which I could have dwelt at length. and among many observations I have selected only those which I thought most likely to interest you. The field is wide and completely unexplored, and at every step a new truth is gleaned, a novel fact observed. How far the results here borne out are capable of prac- tical applications will be decided in the future. As regards the production of light, some results already reached are encouraging, and make me confident in asserting that the practical solution of the problem lies in the direction I have endeavoured to indicate. Still, whatever may be the immediate outcome of these experiments, I am hopeful that they will only prove a step to further development towards the ideal and final perfection. The possibilities which are opened by modern research are so vast that even the most reserved must feel sanguine of the future. Emi- nent scientists consider the problem of utilising one kind of radiation without the others a rational one. In an apparatus designed for the production of light by conversion from any form of energy into that of light, such a. result can never he reached, for no matter what the process of producing the required vibrations, be it electrical, chemical, or any other, it will not be possible to obtain the higher light vibrations without going through the lower heat vibrations. It is the problem of imparting to a body a certain velocity without passing through all lower velocities. But there is a 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 \vill be when this \vill be accom- plished, and the time has come when one may utter such words before an enlightened audience without being con- sidered a visionary. \Ve are whirling through endless space with an inconceivable speed, all around us everything 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 efi`ort, from the store forever inexhaustible, humanity will advance with giant strides. The mere contemplation of these magnificent possibilities expands our minds, strengthens our hopes, and fills our hearts with supreme delight.

82 THE ELECTRICAL ENGINEER, JULY 24, 1891. 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 cha1‘acter. When the currents are rapidly varying in strength, quite different phenomena, often unexpected, present themselves, and quite different laws hold good, which even now have not been determined as fully as is desirable, though through the work, pr‘incipally of English scientists, enough knowledge has been gained on the subject to enable us to treat simple cases which now present them- selves in daily practice. The phenomena which are peculiar to the changing character of the currents are greatly exalted when the rate of change is increased, hence the 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 princi- pally due thatI 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 produc- tion of a practical and efficient source of light. The study of such rapidly alternating 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 instance, we take a piece of iron and hold it against a magnet. Starting from low slternations and running up higher and higher, we feel the impulses succeed each other faster and faster, get weaker and weaker, and finally disappear. \Ve then observe a continuous pull; the pull, of course, is not continuous; it only appears so to us ; our sense of touch is imperfect. \Ve may next establish an arc between the electrodes and observe as the alternations rise that the note which accompanies alternating arcs gets shriller and shriller, gradually weakens, and finally ceases. The air vibrations, of course, continue, but they are too weak to be pe1‘ceivcd ; 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 condenser phenomena, and still more interesting light phenomena with a high-tension induction coil. All these experiments and observations would be of the greatest interest to the student, but their description would lead me too far from the principal subject. Partly for this reason, and partly on account of the vastly greater importance, I will confine myself to the description of the light effects produced by these currents. In the experiments to this end a high-tension induction coil or equivalent apparatus for converting currents of com- paratively low into currents of high tension is used. If you will be sufficiently interested in the results I shall describe as to enter into an experimental study of this subject; if you will be convinced of the truth of the argu- ments I shall advance, your aim will be to produce high frequencies and high potentials-in other words, powerful electrostatic effects. You will then encounter many difficulties, which, if completely overcome, would allow us to produce truly wonderful results. First will be met the didiculty of obtaining the required frequencies by means of mechanical apparatus, and, if they be obtained otherwise, obstacles of a different nature will present themselves. Next it will be found diflicult to pro- vide the requisite insulation without considerably increasing the size of the apparatus, for the potentials required are high, and owing to the rapidity of the alternations the insu- lation presents peculiar difhculties. So, for instance, when a gas is present, the discharge may work by the 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, etc., in fact, through any known insulating substance. The chief requisite in the insulation of the apparatus is, therefore, the exclusion of any gaseous matter. In general, my experience tends to show that bodies which possess the highest specific inductive capacity, such as glass, afford a rather feeble insulation to others, which, while they are good insulators, have a much smaller specific inductive capacity, such as oils, for instance, the it:-.\L\ "r; f / 7%QT '”"`“i“ ' ~1-~‘ ` ._ ~»~,~.;--aff-~» ~~" Q_f`=§77 ..,. , f ` ' "-`37 'f' » ,- : .- “'fE€4 ';f5li‘1 ‘ H ~ Ez, = s~~;;,<§;3

113 obvious that in the experiment described the ball should not be taken too large. In consequence of this twofold tendency it is possible to produce by means of points effects identical to those pro~ duced by capacity. Thus, for instance, by attaching to one terminal of 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 same value as by attaching to the terminal a. polished ball of a surface many times greater than that of the wire. An interesting experiment, showing the effect of the points, may be performed in the following manner : Attach to one of the terminals of the coil a cottorr-covered wire about 2ft. in length, and adjust the conditions so that streams issue from the wire. In this experiment the primary coil should be preferably placed so that it extends only about half \vay into the secondary coil. Now touch the free terminal of the secondary with a conducting object held in the hand, or else connect it to an insulated body of some size. ln this manner the potential on the wire may be enormously raised. Tho effect of this 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 at all allect the streams. In this case the rise of potential is exactly countcracted by the drop through the coil. It will be observed that small lengths of wire produce considerable difference in the magnitude and luminosity of the streams. The primary coil is placed sidewise for two reasons: first, to increase the potential at the wire, and, second, to conceivable, perhaps even obtainable, at which practically the same molecules would strike the terminal. Under such conditions the exchange of the molecules \vorrld be very slow, and the heat produced at, and very near, the terminal would be excessive. But if the frequency would go on increasing constantly, the heat produced would begin to diminish for obvious reasons. In the positive brush ofa static machine the exchange of the molecules is very rapid, the stream is constantly of one direction, and there are fewer collisions, hence the heating effect must be very small. Anything that impairs the facility of exchange tends to increase the local heat produced. Thus, if a bulb be held over the terminal of the coil so as to enclose the brush, the air contained in the bulb is very quickly brought to a high temperature. If a glass tube be held over the brush so as to allow the draught to carry the brush upwards, scorching hot air escapes at the top of the tube. Anything held within the brush is of course rapidly heated, and the possibility of using such heating effects suggests itself. When contemplating this singular phenomenon of the hot brush, we cannot help being convinced that a similar process must take place in the ordinary flame, and it seems strange that after all these centuries past of familiarity with the flame, now, in this era of electric lighting and heating, we are finally led to recognise that since time immemorial we have, after all, al\vays had “ electric light and heat" at our disposal. It is also of no little interest to contemplate that we have a possible way of producing~by other than chemical means-a veritable flame, which would give light and heat without any material being consumed, without any chemical process taking place, and to accomplish this, - f ,» '_ - 1 _ tr-> ' /7 ,rm § rr 1 ‘ ‘ » lf ' ' a‘~" 1 ' s » - r 3-fl: _________ *°;» f_ Q2 f

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