experiments with alternate currents of high potential and high frequency

8/12/2019 Experiments With Alternate Currents of High Potential and High Frequency

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ho!es. ardly have we beco"e fa"iliar with one fact, when novel e!eriences are "et withand new avenues of research are o!ened. Even at this hour !ossibilities not drea"ed ofbefore are, by the use of these currents, !artly reali'ed. s In nature all is ebb and tide, all iswave "otion, so it see"s that in all branches of industry alternating currents&electric wave"otion&will have the sway.

ne reason, !erha!s, why this brand of science is being so ra!idly develo!ed is to be foundin the interest which is attached to its e!eri"ental study. e wind a si"!le ring of iron withcoils( we establish the connections to the generator, and with wonder and delight we note theeffects of strange forces which we bring into !lay, which allow us to transfor", to trans"it anddirect energy at will. e arrange the circuits !ro!erly, and we see the "ass of iron and wiresbehave as though it were endowed with life, s!inning a heavy ar"ature, through invisibleconnections, with great s!eed and !ower with the energy !ossibly conveyed fro" a greatdistance. e observe how the energy of an alternating current traversing the wire "anifestsitself&not so "uch in the wire as in the surrounding s!ace&in the "ost sur!rising "anner,ta#ing the for"s of heat, light, "echanical energy, and, "ost sur!rising of all, even che"icalaffinity. ll these observations fascinate us, and fill us with an intense desire to #now "oreabout the nature of these !heno"ena. Each day we go to our wor# in the ho!e of discovering&in the ho!e that so"e one, no "atter who, "ay find a solution of one of the !ending great

!roble"s,&and each succeeding day we return to our tas# with renewed ardor( and even ifwe areunsuccessful, our wor# has not been in vain, for in these strivings, in these efforts, wehave hours of untold !leasure, and we have directed our energies to the benefit of "an#ind.

e "ay ta#e&at rando", if you choose&any of the "any e!eri"ents which "ay be!erfor"ed with alternating currents( a few of which only, and by no "eans the "ast stri#ing,for" the sub3ect of this evening4s de"onstration( they are all e5ually interesting, e5uallyinciting to thought.

ere is a si"!le glass tube fro" which the air has been !artially ehausted. I ta#e hold of it( Ibring "y body in contact with a wire conveying alternating currents of high !otential, and thetube in "y hand is brilliantly lighted. In whatever !osition I "ay !ut it, wherever I "ay "ove it

in s!ace, as far as I can reach, its soft, !leasing light !ersists with undi"inished brightness.

ere is an ehausted bulb sus!ended fro" a single wire. 7tanding on an insulated su!!ort, Igras! it, and a !latinu" button "ounted in it is brought to vivid incandescence.

ere, attached to a leading wire is another bulb, which, as I touch its "etallic soc#et, is filledwith "agnificent colors of !hos!horescent light.

ere still another, which by "y fingers4 touch casts a shadow&the *roo#es shadow, of theste" inside of it.

ere, again, insulated as I stand on this !latfor", I bring "y body in contact with one of the

ter"inals of the secondary of this induction coil&with the end of a wire "any "iles long&andyou see strea"s of light brea# forth fro" its distant end, which is set in violent vibration.

ere, once "ore, attach these two !lates of wire gau'e to the ter"inals of the coil, I set the"a distance a!art, and I set the coil to wor#. :ou "ay see a s"all s!ar# !ass between the!lates. I insert a thic# !late of one of the best dielectrics between the", and instead ofrendering altogether i"!ossible, as we are used to e!ect, I aidthe !assage of the discharge,which, as I insert the !late, "erely changes in a!!earance and assu"es the for" of lu"inousstrea"s.

Is there, I as#, can there be, a "ore interesting study than that of alternating currents;

In all these investigations, in all these e!eri"ents, which are so very, very interesting, for"any years !ast&ever since the greatest e!eri"enter who lectured in this hall discoveredits !rinci!le&we have had a steady co"!anion, an a!!liance fa"iliar to every one, a


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!laything once, a thing of "o"entous i"!ortance now&the induction coil. $here is no dearera!!liance to the electrician. Fro" the ablest a"ong you, I dare say, down to theine!erienced student, to your lecturer, we all have !assed "any delightful hours ine!eri"enting with the induction coil. e have watched its !lay, and thought and !onderedover the beautiful !heno"ena which it disclosed to our ravished eyes. 7o well #nown is thisa!!aratus, so fa"iliar are these !heno"ena to every one, that "y courage nearly fails "e

when I thin# that I have ventured to address so able an audience, that I have ventured toentertain you with that sa"e old sub3ect. ere in reality is the sa"e a!!aratus, and here arethe sa"e !heno"ena, only the a!!aratus is o!erated so"ewhat differently, the !heno"enaare !resented in a different as!ect. 7o"e of the results we find as e!ected, others sur!riseus, but all ca!tivate our attention, for in scientific investigation each novel result achieved "aybe the centre of a new de!arture, each novel fact learned "ay lead to i"!ortantdevelo!"ents.


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brilliancy, and are acco"!anied by the sa"e shar! crac#ling sound, as those obtained fro" afriction or influence "achine.

nother way is to !ass through two !ri"ary circuits, having a co""on secondary, twocurrents of a slightly different !eriod, which !roduce in the secondary circuit s!ar#s occurringat co"!aratively long intervals. /ut, even with the "eans at hand this evening, I "ay succeedin i"itating the s!ar# of a olt' "achine. For this !ur!ose I establish between the ter"inalsof the coil which charges the condenser a long, unsteady arc, which is !eriodically interru!tedby the u!ward current of air !roduced by it. $o increase the current of air I !lace on each sideof the arc, and close to it, a large !late of "ica. $he condenser charged fro" this coildischarge into the !ri"ary circuit of a second coil through a s"all air ga!, which is necessaryto !roduce a sudden rush of current through the !ri"ary. $he sche"e of connections in the!resent e!eri"ent is indicated in Fig. 2.

Gis an ordinarily constructed alternator, su!!lying the !ri"ary Pof an induction coil, thesecondary Sof which charges the condensers or 3ars C C. $he ter"inals of the secondaryare connected to the inside coatings of the 3ars, the outer coatings being connected to theends of the !ri"aryp pof a second induction coil. $his !ri"aryp phas a s"all air ga! a b.

$he secondary sof this coil is !rovided with #nobs or s!heres K Kof the !ro!er si'e and setat a distance suitable for the e!eri"ent.

long arc is established between the ter"inalsA Bof the first induction coil. M Mare the

"ica !lates.


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Each ti"e the arc is bro#en betweenAand Bthe 3ars are 5uic#ly charged and dischargedthrough the !ri"aryp p, !roducing a sna!!ing s!ar# between the #nobs K K.

hen, instead of o!erating the induction coil as in the last two e!eri"ents, we o!erate itfro" a high fre5uency alternator, as in the net e!eri"ent, a syste"atic study of the!heno"ena is rendered "uch "ore easy. In such case, in varying the strength andfre5uency of the currents through the !ri"ary, we "ay observe five distinct for"s ofdischarge, which I have described in "y for"er !a!er on the sub3ect before the "ericanInstitute of Electrical Engineers, >ay 2?, 1891 @E!eri"ents ith lternate *urrents of Aery

igh Fre5uency and $heir !!lication to >ethods of rtificial Illu"inationB -see$he Electricalorld, 6uly 11, 1891.

It would ta#e too "uch ti"e, and it would lead us too far fro" the sub3ect !resented thisevening, to re!roduce all these for"s, but it see"s to "e desirable to show you one of the".It is a brush discharge, which is interesting in "ore than one res!ect. Aiewed fro" a near!osition it rese"bles "uch a 3et of gas esca!ing under great !ressure. e #now that the!heno"enon is due to the agitation of the "olecules near the ter"inal, and we antici!ate thatso"e heat "ust be develo!ed by the i"!act of the "olecules against the ter"inal or againsteach other. Indeed, we find that the brush is hot, and only a little thought leads us to theconclusion that, could we but reach sufficiently high fre5uencies, we could !roduce a brushwhich would give intense light and heat, and which would rese"ble in every !articular anordinary fla"e, save, !erha!s, that both !heno"ena "ight not be due to the sa"e agent&

save, !erha!s, that che"ical affinity "ight not be electricalin its nature.


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s the !roduction of heat and light is here due to the i"!act of the "olecules, or ato"s of air,or so"ething else besides, and, as we can aug"ent the energy si"!ly by raising the!otential, we "ight, even with fre5uencies obtained fro" a dyna"o "achine, intensify theaction to such a degree as to bring the ter"inal to "elting heat. /ut with such lowfre5uencies we would have to deal always with so"ething of the nature of an electric current.If I a!!roach a conducting ob3ect to the brush, a thin little s!ar# !asses, yet, even with the

fre5uencies used this evening, the tendency to s!ar# is not very great. 7o, for instance, if Ihold a "etallic s!here at so"e distance above the ter"inal you "ay see the whole s!acebetween the ter"inal and s!here illu"inated by the strea"s without the s!ar# !assing( andwith the "uch higher fre5uencies obtainable by the disru!tive discharge of a condenser, wereit not for the sudden i"!ulses, which are co"!aratively few in nu"ber, s!ar#ing would notoccur even at very s"all distances. owever, with inco"!arably higher fre5uencies, whichwe "ay yet find "eans to !roduce efficiently, and !rovided that electric i"!ulses of such highfre5uencies could be trans"itted through a conductor, the electrical characteristics of thebrush discharge would co"!letely vanish&no s!ar# would !ass, no shoc# would be felt&yetwe would still have to deal with an electric!heno"enon, but in the broad, "oderninter!retation of the word. In "y first !a!er before referred to I have !ointed out the curious!ro!erties of the brush, and described the best "anner of !roducing it, but I have thought itworth while to endeavor to e!ress "yself "ore clearly in regard to this !heno"enon,

because of its absorbing interest.

hen a coil is o!erated with currents of very high fre5uency, beautiful brush effects "ay be!roduced, even if the coil be of co"!aratively s"all di"ensions. $he e!eri"enter "ay varythe" in "any ways, and, if it were nothing else, they afford a !leasing sight. hat adds totheir interest is that they "ay be !roduced with one single ter"inal as well as with two&infact, often better with one than with two.

/ut of all the discharge !heno"ena observed, the "ost !leasing to the eye, and the "ostinstructive, are those observed with a coil which is o!erated by "eans of the disru!tivedischarge of a condenser. $he !ower of the brushes, the abundance of the s!ar#s, when theconditions are !atiently ad3usted, is often a"a'ing. ith even a very s"all coil, if it be so wellinsulated as to stand a difference of !otential of several thousand volts !er turn, the s!ar#s"ay be so abundant that the whole coil "ay a!!ear a co"!lete "ass of fire.

*uriously enough the s!ar#s, when the ter"inals of the coil are set at a considerabledistance, see" to dart in every !ossible direction as though the ter"inals were !erfectlyinde!endent of each other. s the s!ar#s would soon destroy the insulation it is necessary to!revent the". $his is best done by i""ersing the coil in a good li5uid insulator, such asboiled%out oil. I""ersion in a li5uid "ay be considered al"ost an absolute necessity for thecontinued and successful wor#ing of such a coil.

It is, of course, out of the 5uestion, in an e!eri"ental lecture, with only a few "inutes atdis!osal for the !erfor"ance of each e!eri"ent, to show these discharge !heno"ena toadvantage, as to !roduce each !heno"enon at its best a very careful ad3ust"ent is re5uired.

/ut even if i"!erfectly !roduced, as they are li#ely to be this evening, they are sufficientlystri#ing to interest an intelligent audience.

/efore showing so"e of these curious effects I "ust, for the sa#e of co"!leteness, give ashort descri!tion of the coil and other a!!aratus used in the e!eri"ents with the disru!tivedischarge this evening.


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It is contained in a bo B-Fig. C of thic# boards of hard wood, covered on the outside with'inc sheet Z, which is carefully soldered all around. It "ight be advisable, in a strictlyscientific investigation, when accuracy is of great i"!ortance, to do away with the "etalcover, as it "ight introduce "any errors, !rinci!ally on account of its co"!le action u!on thecoil, as a condenser of very s"all ca!acity and as an electrostatic and electro"agnetic

screen. hen the coil is used for such e!eri"ents as are here conte"!lated, thee"!loy"ent of the "etal cover offers so"e !ractical advantages, but these are not ofsufficient i"!ortance to be dwelt u!on.

$he coil should be !laced sy""etrically to the "etal cover, and the s!ace between should, ofcourse, not be too s"all, certainly not less than, say, five centi"eters, but "uch "ore if!ossible( es!ecially the two sides of the 'inc bo, which are at right angles to the ais of thecoil, should be sufficiently re"ote fro" the latter, as otherwise they "ight i"!air its action andbe a source of loss.

$he coil consists of two s!ools of hard rubber R Rheld a!art at a distance of 1? centi"etresby bolts cand nuts n, li#ewise of hard rubber. Each s!ool co"!rises a tube Tofa!!roi"ately 8 centi"etres inside dia"eter, and C "illi"etres thic#, u!on which are screwedtwo flanges F F, 2 centi"etres s5uare, the s!ace between the flanges being about Ccenti"etres. $he secondary, S S, of the best gutta !ercha%covered wire, has 2 layers, 1?turns in each, giving for each half a total of 2? turns. $he two halves are wound o!!ositelyand connected in series, the connection between both being "ade over the !ri"ary. $hisdis!osition besides being convenient, has the advantage that when the coil is well balanced&that is, when both of its ter"inals T1T1are connected to bodies or devices of e5ual ca!acity&there is not "uch danger of brea#ing through to the !ri"ary, and the insulation between the!ri"ary and the secondary need not be thic#. In using the coil it is advisable to attachto bothter"inals devices of nearly e5ual ca!acity, as, when the ca!acity of the ter"inals isnot e5ual, s!ar#s will be a!t to !ass to the !ri"ary. $o avoid this, the "iddle !oint of thesecondary "ay be connected to the !ri"ary, but this is not always !racticable.

$he !ri"ary P Pis wound in two !arts, and o!!ositely, u!on a wooden s!ool W, and the fourends are led out of the oil through hard rubber tubes t t. $he ends of the secondary T1T1arealso led out of the oil through rubber tubes t1t1of great thic#ness. $he !ri"ary and


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secondary layers are insulated by cotton cloth, the thic#ness of the insulation, of course,bearing so"e !ro!ortion to the difference of !otential between the turns of the differentlayers. Each half of the !ri"ary has four layers, 2 turns in each, this giving a total of 9turns. hen both the !arts are connected in series, this gives a ratio of conversion of about1)2., and with the !ri"aries in "ulti!le, 1)G. but in o!erating with very ra!idly alternatingcurrents this ratio does not convey even an a!!roi"ate idea of the ratio of the E.>.Fs. in the

!ri"ary and secondary circuits. $he coil is held in !osition in the oil on wooden su!!orts,there being about G centi"etres thic#ness of oil all round. here the oil is not s!eciallyneeded, the s!ace is filled with !ieces of wood, and for this !ur!ose !rinci!ally the woodenbo / surrounding the whole is used.

$he construction here shown is, of course, not the best on general !rinci!les, but I believe it isa good and convenient one for the !roduction of effects in which an ecessive !otential and avery s"all current are needed.

In connection with the coil I use either the ordinary for" of discharger or a "odified for". Inthe for"er I have introduced two changes which secure so"e advantages, and which areobvious. If they are "entioned, it is only in the ho!e that so"e e!eri"enter "ay find the" ofuse.

ne of the changes is that the ad3ustable #nobsAand B-Fig. , of the discharger are held in3aws of brass, J J, by s!ring !ressure, this allowing of turning the" successively into different!ositions, and so doing away with the tedious !rocess of fre5uent !olishing u!.

$he other change consists in the e"!loy"ent of a strong electro"agnet N S, which is !lacedwith its ais at right angles to the line 3oining the #nobsAand B, and !roduces a strong"agnetic field between the". $he !ole !ieces of the "agnet are "ovable and !ro!erlyfor"ed so as to !rotrude between the brass #nobs, in order to "a#e the field as intense as!ossible( but to !revent the discharge fro" 3u"!ing to the "agnet the !ole !ieces are!rotected by a layer of "ica, M M, of sufficient thic#ness, slsland s2s2are screws forfastening the wires. n each side one of the screws is for large and the other for s"allwires. L Lare screws for fiing in !osition the rods R R, which su!!ort the #nobs.

In another arrange"ent with the "agnet I ta#e the discharge between the rounded !ole!ieces the"selves, which in such case are insulated and !referably !rovided with !olishedbrass ca!s.

$he e"!loy"ent of an intense "agnetic field is of advantage !rinci!ally when the inductioncoil or transfor"er which charges the condenser is o!erated by currents of very lowfre5uency. In such a case the nu"ber of the funda"ental discharges between the #nobs "aybe so s"all as to render the currents !roduced in the secondary unsuitable for "anye!eri"ents. $he intense "agnetic field then serves to blow out the arc between the #nobsas soon as it is for"ed, and the funda"ental discharges occur in 5uic#er succession.


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Instead of the "agnet, a draught or blast of air "ay be e"!loyed with so"e advantage. Inthis case the arc is !referably established between the #nobs A B, in Fig. 2 -the #nobs abbeing generally 3oined, or entirely done away with, as in this dis!osition the arc is long andunsteady, and is easily affected by the draught.

hen a "agnet is e"!loyed to brea# the arc, it is better to choose the connection indicateddiagra""atically in Fig G, as in this case the currents for"ing the arc are "uch "ore!owerful, and the "agnetic field eercises a greater influence. $he use of the "agnet!er"its, however, of the arc being re!laced by a vacuu" tube, but I have encountered great

difficulties in wor#ing with an ehausted tube.

$he other for" of discharger used in these and si"ilar e!eri"ents is indicated in Figs. and. It consists of a nu"ber of brass !ieces c c-Fig. , each of which co"!rises a s!herical"iddle !ortion " with an etension e below&which is "erely used to fasten the !iece in alathe when !olishing u! the discharging surface&and a colu"n above, which consists of a#nurled flange f sur"ounted by a threaded ste" I carrying a nut n, by "eans of which a wireis fastened to the colu"n. $he flange fconveniently serves for holding the brass !iece whenfastening the wire, and also for turning it in any !osition when it beco"es necessary to!resent a fresh discharging surface. $wo stout stri!s of hard rubber R R, with !lanedgrooves -Fig. to fit the "iddle !ortion of the !ieces c c, serve to cla"! the latter andhold the" fir"ly in !osition by "eans of two bolts C C-of which only one is shown !assingthrough the ends of the stri!s.


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In the use of this #ind of discharger I have found three !rinci!al advantages over the ordinaryfor". First, the dielectric strength of a given total width of air s!ace is greater when a great"any s"all air ga!s are used instead of one, which !er"its of wor#ing with a s"aller lengthof air ga!, and that "eans s"aller loss and less deterioration of the "etal( secondly byreason of s!litting the arc u! into s"aller arcs, the !olished surfaces are "ade to last "uchlonger( and, thirdly, the a!!aratus affords so"e gauge in the e!eri"ents. I usually set the

!ieces by !utting between the" sheets of unifor" thic#ness at a certain very s"all distancewhich is #nown fro" the e!eri"ents of 7ir illia" $ho"son to re5uire a certainelectro"otive force to be bridged by the s!ar#.

It should, of course, be re"e"bered that the s!ar#ing distance is "uch di"inished as thefre5uency is increased. /y ta#ing any nu"ber of s!aces the e!eri"enter has a rough ideaof the electro"otive force, and he finds it easier to re!eat an e!eri"ent, as he has not thetrouble of setting the #nobs again and again. ith this #ind of discharger I have been able to"aintain an oscillating "otion without any s!ar# being visible with the na#ed eye between the#nobs, and they would not show a very a!!reciable rise in te"!erature. $his for" ofdischarger also lends itself to "any arrange"ents of condensers and circuits which are oftenvery convenient and ti"esaving. I have used it !referably in a dis!osition si"ilar to thatindicated in Fig. 2, when the currents for"ing the arcs are s"all.

I "ay here "ention that I have also used dischargers with single or "ulti!le air ga!s, in whichthe discharge surfaces were rotated with great s!eed. =o !articular advantage was,however, gained by this "ethod, ece!t in cases where the currents fro" the condenser werelarge and the #ee!ing cool of the surfaces was necessary, and in cases when, the dischargenot being oscillating of itself, the arc as soon as established was bro#en by the air current,thus starting the vibration at intervals in ra!id succession. I have also used "echanicalinterru!ters in "any ways. $o avoid the difficulties with frictional contacts, the !referred !lanado!ted was to establish the arc and rotate through it at great s!eed a ri" of "ica !rovidedwith "any holes and fastened to a steel !late.

It is understood, of course, that the e"!loy"ent of a "agnet, air current, or other interru!ter,

!roduces an effect worth noticing, unless the self%induction, ca!acity and resistance are sorelated that there are oscillations set u! u!on each interru!tion.

I will now endeavor to show you so"e of the "ost noteworthy of these discharge !heno"ena.

I have stretched across the roo" two ordinary cotton covered wires, each about "etres inlength. $hey are su!!orted on insulating cords at a distance of about C? centi"etres. Iattach now to each of the ter"inals of the coil one of the wires and set the coil in action.

convenient way is to use an oil condenser of very s"all ca!acity, consisting of two s"allad3ustable "etal !lates, in connection with this and si"ilar e!eri"ents. In such case I ta#ewires rather short and set at the beginning the condenser !lates at "ai"u" distance. If thestrea"s for the wires increase by a!!roach of the !lates, the length of the wires is about right(if they di"inish the wires are too long for that fre5uency and !otential. hen a condenser isused in connection with e!eri"ents with such a coil, it should be an oil condenser by all"eans, as in using an air condenser considerable energy "ight be wasted. $he wires leadingto the !lates in the oil should be very thin, heavily coated with so"e insulating co"!ound, and!rovided with a conducting covering&this !referably etending under the surface of the oil.$he conducting cover should not be too near the ter"inals, or ends, of the wire, as a s!ar#


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would be a!t to 3u"! fro" the wire to it. $he conducting coating is used to di"inish the airlosses, in virtue of its action as an electrostatic screen. s to the si'e of the vessel containingthe oil and the site of the !lates, the e!eri"enter gains at once an idea fro" a rough trial.$he si'e of the !lates in oilis, however, calculable, as the dielectric losses are very s"all.

In the !receding e!eri"ent it is of considerable interest to #now what relation the 5uantity of

the light e"itted bears to the fre5uency and !otential of the electric i"!ulses. >y o!inion isthat the heat as well as light effects !roduced should be !ro!ortionate, under otherwise e5ualconditions of test, to the !roduct of fre5uency and s5uare of !otential, but the e!eri"entalverification of the law, whatever it "ay be, would be eceedingly difficult. ne thing is certain,at any rate, and that is, that in aug"enting the !otential and fre5uency we ra!idly intensify thestrea"s( and, though it "ay be very sanguine, it is surely not altogether ho!eless to e!ectthat we "ay succeed in !roducing a !ractical illu"inant on these lines. e would then besi"!ly using burners or fla"es, in which there would be no che"ical !rocess, noconsu"!tion of "aterial, but "erely a transfer of energy, and which would, in all !robabilitye"it "ore light and less heat than ordinary fla"es.

$he lu"inous intensity of the strea"s is, of course, considerably increased when they arefocused u!on a s"all surface. $his "ay be shown by the following e!eri"ent)

I attach to one of the ter"inals of the coil a wire w -Fig. 8, bent in a circle of about C?centi"etres in dia"eter, and to the other ter"inal I fasten a s"all brass s!here s, the surfaceof the wire being !referably e5ual to the surface of the s!here, and the centre of the latterbeing in a line at right angles to the !lane of the wire circle and !assing through its centre.hen the discharge is established under !ro!er conditions, a lu"inous hollow cone isfor"ed, and in the dar# one%half of the brass s!here is strongly illu"inated, as shown in thecut.

/y so"e artifice or other, it is easy to concentrate the strea"s u!on s"all surfaces and to!roduce very strong light effects. $wo thin wires "ay thus be rendered intensely lu"inous. Inorder to intensify the strea"s, the wires should be very thin and short( but as in this case theirca!acity would be generally too s"all for the coil&at least, for such a one as the !resent&it

is necessary to aug"ent the ca!acity to the re5uired value, while, al the sa"e ti"e, thesurface of the wires re"ains very s"all. $his "ay be done in "any ways.


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hen an ordinary low fre5uency discharge is !assed through "oderately rarefied air, the airassu"es a !ur!lish hue. If by so"e "eans or other we increase the intensity of the"olecular, or ato"ic, vibration, the gas changes to a white color. si"ilar change occurs atordinary !ressures with electric i"!ulses of very high fre5uency. If the "olecules of the airaround a wire are "oderately agitated, the brush for"ed is reddish or violet( if the vibration isrendered sufficiently intense, the strea"s beco"e white. e "ay acco"!lish this in various

ways. In the e!eri"ent before shown with the two wires across the roo", I haveendeavored to secure the result by !ushing to a high value both the fre5uency and !otential(in the e!eri"ent with the thin wires glued on the rubber !late I have concentrated the actionu!on a very s"all surface&in other words, I have wor#ed with a great electric density.

"ost curious for" of discharge is observed with such a coil when the fre5uency and!otential are !ushed to the etre"e li"it. $o !erfor" the e!eri"ent, every !art of the coilshould be heavily insulated, and only two s"all s!heres&or, better still, two shar!%edged"etal discs -d d, Fig. 11 of no "ore than a few centi"etres in dia"eter&should be e!osedto the air. $he coil here used i""ersed in oil, and the ends of the secondary reaching out ofthe oil are covered with an airtight cover of hard rubber of great thic#ness. ll crac#s, if thereare any, should be carefully sto!!ed u!, so that the brush discharge cannot for" anywhereece!t on the s"all s!heres or !lates which are e!osed to the air. In this case, since thereare no large !lates or other bodies of ca!acity attached to the ter"inals, the coil is ca!able ofan etre"ely ra!id vibration. $he !otential "ay be raised by increasing, as far as thee!eri"enter 3udges !ro!er, the rate of change of the !ri"ary current. ith a coil not widelydiffering fro" the !resent, it is best to connect the two !ri"aries in "ulti!le arc( but if the

secondary should have a "uch greater nu"ber of turns the !ri"aries should !referably beused in series, as otherwise the vibration "ight be too fast for the secondary. It occurs underthese conditions that "isty white strea"s brea# forth fro" the edges of the discs and s!readout !hanto"%li#e into s!ace. ith this coil, when fairly well !roduced, they are about 2G to C?centi"etres long. hen the hand is held against the" no sensation is !roduced, and as!ar#, causing a shoc#, 3u"!s fro" the ter"inal only u!on the hand being brought "uchnearer. If the oscillation of the !ri"ary current is rendered inter"ittent by so"e "eans orother, there is a corres!onding throbbing of the strea"s, and now the hand or otherconducting ob3ect "ay be brought in still greater !roi"ity to the ter"inal without a s!ar#being caused to 3u"!.

"ong the "any beautiful !heno"ena which "ay be !roduced with such a coil I have hereselected only those which a!!ear to !ossess so"e features of novelty, and lead us to so"e

conclusions of interest. ne will not find it at all difficult to !roduce in the laboratory, by"eans of it, "any other !heno"ena which a!!eal to the eye even "ore than these hereshown, but !resent no !articular feature of novelty.


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Early e!eri"enters describe the dis!lay of s!ar#s !roduced by an ordinary large inductioncoil u!on an insulating !late se!arating the ter"inals. Huite recently 7ie"ens !erfor"edso"e e!eri"ents in which fine effects were obtained, which were seen by "any withinterest. =o doubt large coils, even if o!erated with currents of low fre5uencies, are ca!ableof !roducing beautiful effects. /ut the largest coil ever "ade could not, by far, e5ual the"agnificent dis!lay of strea"s and s!ar#s obtained fro" such a disru!tive discharge coil

when !ro!erly ad3usted. $o give an idea, a coil such as the !resent one will cover easily a!late of 1 "etre in dia"eter co"!letely with the strea"s. $he best way to !erfor" suche!eri"ents is to ta#e a very thin rubber or a glass !late and glue on one side of it a narrowring of tinfoil of very large dia"eter, and on the other a circular washer, the centre of the lattercoinciding with that of the ring, and the surfaces of both being !referably e5ual, so as to #ee!the coil well balanced. $he washer and ring should be connected to the ter"inals by heavilyinsulated thin wires. It is easy in observing the effect of the ca!acity to !roduce a sheet ofunifor" strea"s, or a fine networ# of thin silvery threads, or a "ass of loud brilliant s!ar#s,which co"!letely cover the !late.

7ince I have advanced the idea of the conversion by "eans of the disru!tive discharge, in "y!a!er before the "erican Institute of Electrical Engineers at the beginning of the !ast year,the interest ecited in it has been considerable. It affords us a "eans for !roducing any

!otentials by the aid of ine!ensive coils o!erated fro" ordinary syste"s of distribution, and&what is !erha!s "ore a!!reciated&it enables us to convert currents of any fre5uency intocurrents of any other lower or higher fre5uency. /ut its chief value will !erha!s be found inthe hel! which it will afford us in the investigations of the !heno"ena of !hos!horescence,which a disru!tive discharge coil is ca!able of eciting in innu"erable cases where ordinarycoils, even the largest, would utterly fail.

*onsidering its !robable uses for "any !ractical !ur!oses, and its !ossible introduction intolaboratories for scientific research, a few additional re"ar#s as to the construction of such acoil will !erha!s not be found su!erfluous.

It is, of course, absolutely necessary to e"!loy in such a coil wires !rovided with the best

insulation.

ood coils "ay be !roduced by e"!loying wires covered with several layers of cotton, boilingthe coil a long ti"e in !ure wa, and cooling under "oderate !ressure. $he advantage ofsuch a coil is that it can be easily handled, but it cannot !robably give as satisfactory resultsas a coil i""ersed in !ure oil. /esides, it see"s that the !resence of a large body of waaffects the coil disadvantageously, whereas this does not see" to be the case with oil.0erha!s it is because the dielectric losses in the li5uid are s"aller.

I have tried at first sil# and cotton covered wires with oil i""ersion( but I have been graduallyled to use gutta%!ercha covered wires, which !roved "ost satisfactory. utta%!erchainsulation adds, of course, to the ca!acity of the coil, and this, es!ecially if the coil be large, isa great disadvantage when etre"e fre5uencies are desired( but, on the other hand, gutta%

!ercha will withstand "uch "ore than an e5ual thic#ness of oil, and this advantage should besecured at any !rice. nce the coil has been i""ersed, it should never be ta#en out of theoil for "ore than a few hours, else the gutta%!ercha will crac# u! and the coil will not be worthhalf as "uch as before. utta%!ercha is !robably slowly attac#ed by the oil, but after ani""ersion of eight to nine "onths I have found no ill effects.

I have obtained in co""erce two #inds of gutta%!ercha wire) in one the insulation stic#s tightlyto the "etal, in the other it does not.


16/57

been for a long ti"e boiled in oil. $he boards should be so 3oined as to safely withstand theeternal air !ressure. $he coil being !laced and fastened in !osition within the bo, the latteris closed with a strong lid, and covered with closely fitting "etal sheets, the 3oints of which aresoldered very carefully. n the to! two s"all holes are drilled, !assing through the "etalsheet and the wood, and in these holes two s"all glass tubes are inserted and the 3oints"ade air%tight. ne of the tubes is connected to a vacuu" !u"! and the other with a vessel

containing a sufficient 5uantity of boiled%out oil. $he latter tube has a very s"all hole at thebotto", and is !rovided with a sto!coc#. hen a fairly good vacuu" has been obtained, thesto!coc# is o!ened and the oil slowly fed in. 0roceeding in this "anner, it is i"!ossible thatany big bubbles, which are the !rinci!al danger, should re"ain between the turns. $he air is"ost co"!letely ecluded, !robably better than by boiling out, which, however, when gutta%!ercha coated wires are used, is not !racticable.

For the !ri"aries I use ordinary line wire with thic# cotton coating. 7trands of very thininsulated wires !ro!erly interlaced would, of course, be the best to e"!loy for the !ri"aries,but they are not to be had.

In an e!eri"ental coil the si'e of the wires is not of great i"!ortance. In the coil here usedthe !ri"ary is =o, 12 and the secondary =o. 2 /rown 7har!e gauge wire( but the sections"aybe varied considerably. I would only i"!ly different ad3ust"ents( the results ai"ed atwould not be "aterially affected.

I have dwelt at so"e length u!on the various for"s of brush discharge because, in studyingthe", we not only observe !heno"ena which !lease our eye, but also afford us food forthought, and lead us to conclusions of !ractical i"!ortance. In the use of alternating currentsof very high tension, too "uch !recaution cannot be ta#en to !revent the brush discharge. Ina "ain conveying such currents, in an induction coil or transfor"er, or in a condenser, thebrush discharge is a source of great danger to the insulation. In a condenser es!ecially thegaseous "atter "ust be "ost carefully e!elled, for in it the charged surfaces are near eachother, and if the !otentials are high, 3ust as sure as a weight will fall if let go, so the insulationwill give way if a single gaseous bubble of so"e site be !resent, whereas, if all gaseous

"atter were carefully ecluded, the condenser would safely withstand a "uch higherdifference of !otential. "ain conveying alternating currents of very high tension "ay bein3ured "erely by a blowhole or s"all crac# in the insulation, the "ore so as a blowhole is a!tto contain gas at low !ressure( and as it a!!ears al"ost i"!ossible to co"!letely obviatesuch little i"!erfections, I a" led to believe that in our future distribution of electrical energyby currents of very high tension li5uid insulation will be used. $he cost is a great drawbac#,but if we e"!loy an oil as an insulator the distribution of electrical energy with so"ething li#e1??,??? volts, and even "ore, beco"e, at least with higher fre5uencies, so easy that theycould be hardly called engineering feats. ith oil insulation and alternate current "otorstrans"issions of !ower can be effected with safety and u!on an industrial basis at distancesof as "uch as a thousand "iles.

!eculiar !ro!erty of oils, and li5uid insulation in general, when sub3ected to ra!idly changing

electric stresses, is to dis!erse any gaseous bubbles which "ay be !resent, and diffuse the"through its "ass, generally long before any in3urious brea# can occur. $his feature "ay beeasily observed with an ordinary induction coil by ta#ing the !ri"ary out, !lugging u! the endof the tube u!on which the secondary is wound, and fining it with so"e fairly trans!arentinsulator, such as !araffin oil. !ri"ary of s dia"eter so"ething li#e si "illi"etres s"allerthan the inside of the tube "ay be inserted in the oil. hen the coil is set to wor# one "aysee, loo#ing fro" the to! through the oil, "any lu"inous !oints&air bubbles which are caughtby inserting the !ri"ary, and which ate rendered lu"inous in conse5uence of the violentbo"bard"ent. $he occluded air, by its i"!act against the oil, beats it( the oil begins tocirculate, carrying so"e of the air along with it, until the bubbles are dis!ersed and thelu"inous !oints disa!!ear. In this "anner, unless large bubbles are occluded in such waythat circulation is rendered i"!ossible, a da"aging brea# is averted, the only effect being a"oderate war"ing u! of the oil. If, instead of the li5uid, a solid insulation, no "atter how

thic#, were used, a brea#ing through and in3ury of the a!!aratus would be inevitable.


17/57

$he eclusion of gaseous "atter fro" any a!!aratus in which the dielectric is sub3ected to"ore or less ra!idly changing electric forces is, however, not only desirable in order to avoid a!ossible in3ury of the a!!aratus, but also on account of econo"y. In a condenser, forinstance, as long as only a solid or only a li5uid dielectric is used, the loss is s"all( but if agas under ordinary or s"all !ressure be !resent the loss "ay be very great. hatever thenature of the force acting in the dielectric "ay be, it see"s that in a solid or li5uid the

"olecular dis!lace"ent !roduced by the force is s"all) hence the !roduct of force anddis!lace"ent is insignificant, unless the force be very great( but in a gas the dis!lace"ent,and, therefore, this !roduct is considerable( the "olecules are free to "ove, they reach highs!eeds, and the energy of their i"!act is lost in heat or otherwise. If the gas be stronglyco"!ressed, the dis!lace"ent due to the force is "ade s"aller, and the losses are reduced.

In "ost of the succeeding e!eri"ents I !refer, chiefly on account of the regular and !ositiveaction, to e"!loy the alternator before referred to. $his is one of the several "achinesconstructed by "e for the !ur!oses of these investigations. It has C8 !ole !ro3ections, andis ca!able of giving currents of a fre5uency of about 1?,??? !er second. $his "achine hasbeen illustrated and briefly described in "y first !a!er before the "erican Institute ofElectrical Engineers, >ay 2?, 18C1, to which I have already referred. "ore detaileddescri!tion, sufficient to enable any engineer to build a si"ilar "achine, will be found in

several electrical 3ournals of that !eriod.

$he induction coils o!erated fro" the "achine are rather s"all, containing fro" G,??? to1G,??? turns in the secondary. $hey are i""ersed in boiled%out linseed oil, contained inwooden boes covered with 'inc sheet.

I have found it advantageous to reverse the usual !osition of the wires, and to wind, in thesecoils, the !ri"aries on the to!( this allowing the use of a "uch bigger !ri"ary, which, ofcourse, reduces the danger of overheating and increases the out!ut of the coil. I "a#e the!ri"ary on each side at least one centi"etre shorter than the secondary, to !revent thebrea#ing through on the ends, which would surely occur unless the insulation on the to! of thesecondary be very thic#, and this, of course, would be disadvantageous.

hen the !ri"ary is "ade "ovable, which is necessary in so"e e!eri"ents, and "anyti"es convenient for the !ur!oses of ad3ust"ent, I cover the secondary with wa, and turn itoff in a lathe to a dia"eter slightly s"aller than the inside of the !ri"ary coil. $he latter I!rovide with a handle reaching out of the oil, which serves to shift it in any !osition along thesecondary.

I will now venture to "a#e, in regard to the general "ani!ulation of induction coils, a fewobservations bearing u!on !oints which have not been fully a!!reciated in earliere!eri"ents with such coils, and are even now often overloo#ed.

$he secondary of the coil !ossesses usually such a high self%induction that the currentthrough the wire is ina!!reciable, and "ay be so even when the ter"inals ate 3oined by aconductor of s"all resistance. If ca!acity is added to the ter"inals, the self%induction iscounteracted, and a stronger current is "ade to flow through the secondary, though itster"inals are insulated fro" each other. $o one entirely unac5uainted with the !ro!erties ofalternating currents nothing will loo# "ore !u''ling. $his feature was illustrated in thee!eri"ent !erfor"ed at the beginning with the to! !lates of wire gau'e attached to theter"inals and the rubber !late. hen the !lates of wire gau'e were close together, and as"all arc !assed between the", the arcpre$enteda strong current fro" !assing through thesecondary, because it did away with the ca!acity on the ter"inals( when the rubber !late wasinserted between, the ca!acity of the condenser for"ed counteracted the self%induction of thesecondary, a stronger current !assed now, the coil !erfor"ed "ore wor#, and the dischargewas by far "ore !owerful.

$he first thing, then, in o!erating the induction coil is to co"bine ca!acity with the secondaryto overco"e the self%induction. If the fre5uencies and !otentials are very high gaseous"atter should be carefully #e!t away fro" the charged surfaces. If Leyden 3ars are used,


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19/57

and acts inductively u!on the "oderately rarefied and highly conducting gas enclosed in thenec#. Fro" there the current !asses through the tube binto the s"all s!here s, to act byinduction u!on the gas contained in the globe L.

It is of advantage to "a#e the tube tvery thic#, the hole through it very s"all, and to blow thes!here svery thin. It is of the greatest i"!ortance that the s!here sbe !laced in the centre of

the globe L.

Figs. 1, 1G and 1 indicate different for"s, or stages, of the brush. Fig. 1 shows the brushas it first a!!ears in a bulb !rovided with a conducting ter"inal) but, as in such a bulb it verysoon disa!!ears&often after a few "inutes&I will confine "yself to the descri!tion of the!heno"enon as seen in a bulb without conducting electrode. It is observed under thefollowing conditions)

hen the globe L-Figs. 12 and 1C is ehausted to a very high degree, generally the bulb isnot ecited u!on connecting the wire !-Fig. 12 or the tinfoil coating of the bulb -Fig. 1C tothe ter"inal of the induction coil. $o ecite it, it is usually sufficient to gras! the globe Lwiththe hand. n intense !hos!horescence then s!reads at first over the globe, but soon gives!lace to a white, "isty light. 7hortly afterward one "ay notice that the lu"inosity is unevenlydistributed in the globe, and after !assing the current for so"e ti"e the bulb a!!ears as inFig. 1G. Fro" this stage the !heno"enon will gradually !ass to that indicated in Fig. 1, afterso"e "inutes, hours, days or wee#s, according as the bulb is wor#ed. ar"ing the bulb orincreasing the !otential hastens the transit.


20/57

hen the brush assu"es the for" indicated in Fig. 1, it "ay be brought to a state ofetre"e sensitiveness to electrostatic and "agnetic influence. $he bulb hanging straightdown fro" a wire, and all ob3ects being re"ote fro" it, the a!!roach of the observer at a few!aces fro" the bulb will cause the brush to fly to the o!!osite side, and if he wal#s around thebulb it will always #ee! on the o!!osite side. It "ay begin to s!in around the ter"inal longbefore it reaches that sensitive stage. hen it begins to turn around !rinci!ally, but also

before, it is affected by a "agnet and at a certain stage it is susce!tible to "agnetic influenceto an astonishing degree. s"all !er"anent "agnet, with its !oles at a distance of no "orethan two centi"etres, will affect it visibly at a distance of two "etres, slowing down oraccelerating the rotation according to how it is held relatively to the brush. I thin# I haveobserved that at the stage when it is "ost sensitive to "agnetic, it is not "ost sensitive toelectrostatic, influence. >y e!lanation is, that the electrostatic attraction between the brushand the glass of the bulb, which retards the rotation, grows "uch 5uic#er than the "agneticinfluence when the intensity of the strea" is increased.

hen the bulb hangs with the globe Ldown, the rotation is always cloc#wise. In the southernhe"is!here it would occur in the o!!osite direction and on the e5uator the brush should notturn at all. $he rotation "ay be reversed by a "agnet #e!t at so"e distance. $he brushrotates best, see"ingly, when it is at right angles to the lines of force of the earth. It very

li#ely rotates, when at its "ai"u" s!eed, in synchronis" with the alternations, say 1?,???ti"es a second. $he rotation can be slowed down or accelerated by the a!!roach or recedingof the observer or any conducting body, but it cannot be reversed by !utting the bulb in any!osition. hen it is in the state of the highest sensitiveness and the !otential or fre5uency bevaried the sensitiveness is ra!idly di"inished. *hanging either of these but little will generallysto! the rotation. $he sensitiveness is li#ewise affected by the variations of te"!erature. $oattain great sensitiveness it is necessary to have the s"all s!here s in the centre of theglobe L, as otherwise the electrostatic action of the glass of the globe will tend to sto! therotation. $he s!here sshould be s"all and of unifor" thic#ness( any dissy""etry of coursehas the effect to di"inish the sensitiveness.

$he fact that the brush rotates in a definite direction in a !er"anent "agnetic field see"s toshow that in alternating currents of very high fre5uency the !ositive and negative i"!ulsesare not e5ual, but that one always !re!onderates over the other.

f course, this rotation in one direction "ay be due to the action of two ele"ents of the sa"ecurrent u!on each other, or to the action of the field !roduced by one of the ele"ents u!onthe other, as in a series "otor, without necessarily one i"!ulse being stronger than the other.$he fact that the brush turns, as far as I could observe, in any !osition, would s!ea# for thisview. In such case it would turn at any !oint of the earth4s surface. /ut, on the other hand, itis then hard to e!lain why a !er"anent "agnet should reverse the rotation, and one "ustassu"e the !re!onderance of i"!ulses of one #ind.

s to the causes of the for"ation of the brush or strea", I thin# it is due to the electrostaticaction of the globe and the dissy""etry of the !arts. If the s"all bulb s and the globe Lwere

!erfect concentric s!heres, and the glass throughout of the sa"e thic#ness and 5uality, I thin#the brush would not for", as the tendency to !ass would be e5ual on all sides. $hat thefor"ation of the strea" is due to an irregularity is a!!arent fro" the fact that it has thetendency to re"ain in one !osition, and rotation occurs "ost generally only when it is broughtout of this !osition by electrostatic or "agnetic influence. hen in an etre"ely sensitivestate it rests in one !osition, "ost curious e!eri"ents "ay be !erfor"ed with it. Forinstance, the e!eri"enter "ay, try selecting a !ro!er !osition, a!!roach the hand at acertain considerable distance to the bulb, and he "ay cause the brush to !ass off by "erelystiffening the "uscles of the ar". hen it begins to rotate slowly, and the hands are held at a!ro!er distance, it is i"!ossible to "a#e even the slightest "otion without !roducing a visibleeffect u!on the brush. "etal !late connected to the other ter"inal of the coil affects it at agreat distance, slowing down the rotation often to one turn a second.

I a" fir"ly convinced that such a brush, when we learn how to !roduce it !ro!erly, will !rovea valuable aid in the investigation4 of the nature of the forces acting in an electrostatic or


21/57

"agnetic field. If there is any "otion which is "easurable going on in the s!ace, such abrush ought to reveal it. It is, so to s!ea#, a bea" of light, frictionless, devoid of inertia.

I thin# that it "ay find !ractical a!!lications in telegra!hy. ith such a brush it would be!ossible to send dis!atches across the tlantic, for instance, with any s!eed, since itssensitiveness "ay be so great that the slightest changes will affect it. If it were !ossible to

"a#e the strea" "ore intense and very narrow, its deflections could be easily !hotogra!hed.

I have been interested to find whether there is a rotation of the strea" itself, or whether thereis si"!ly a stress traveling around in the bulb. For this !ur!ose I "ounted a light "ica fan sothat its vanes were in the !ath of the brush. If the strea" itself was rotating the fan would bes!un around. I could !roduce no distinct rotation of the fan, although I tried the e!eri"entre!eatedly( but as the fan eerted a noticeable influence on the strea", and the a!!arentrotation of the latter was, in this case, never 5uite satisfactory, the e!eri"ent did not a!!earto be conclusive.

I have been unable to !roduce the !heno"enon with the disru!tive discharge coil, althoughevery other of these !heno"ena can be tell !roduced by it&"any, in fact, "uch better than

with coils o!erated fro" an alternator.

It "ay be !ossible to !roduce the brush by i"!ulses of one direction, or even by a steady!otential, in which case it would be still "ore sensitive to "agnetic influence.

In o!erating an induction coil with ra!idly alternating currents, we reali'e with astonish"ent,for the first ti"e, the great i"!ortance of the relation of ca!acity, self%induction and fre5uencyas regards the general result. $he effects of ca!acity are the "ost stri#ing, for in thesee!eri"ents, since the self%induction and fre5uency both are high, the critical ca!acity is verys"all, and need be but slightly varied to !roduce a very considerable change. $hee!eri"enter "ay bring his body in contact with the ter"inals of the secondary of the coil, orattach to one or both ter"inals insulated bodies of very s"all bul#, such as bulbs, and he "ay!roduce a considerable rise or fall of !otential, and greatly affect the flow of the current

through the !ri"ary. In the e!eri"ent before shown, in which a brush a!!ears at a wireattached to one ter"inal, and the wire is vibrated when the e!eri"enter brings his insulatedbody in contact with the other ter"inal of the coil, the sudden rise of !otential was "adeevident.

I "ay show you the behavior of the coil in another "anner which !ossesses a feature ofso"e interest. I have here a little light fan of alu"iniu" sheet, fastened to a needle andarranged to rotate freely in a "etal !iece screwed to one of the ter"inals of the coil. henthe coil is set to wor#, the "olecules of the air are rhyth"ically attracted and re!elled. s theforce with which they are re!elled is greater than that with which they are attracted, it resultsthat there is re!ulsion eerted on the surfaces of the fan. If the fan were "ade si"!ly of a"etal sheet, the re!ulsion would be e5ual on the o!!osite sides, and would !roduce noeffect. /ut if one of the o!!osite surfaces is screened, or if, generally s!ea#ing, thebo"bard"ent on this side is wea#ened in so"e wag or other, there re"ains the re!ulsioneerted u!on the other, and the fan is set in rotation. $he screening is best effected byfastening u!on one of the o!!osing sides of the fan insulated conducting coatings, or, if thefan is "ade in the sha!e of an ordinary !ro!eller screw, by fastening on one side, and closeto it, an insulated "etal !late. $he static screen "ay however, be o"itted and si"!ly athic#ness of insulating "aterial fastened to one of the sides of the fan.

$o show the behavior of the coil, the fan "ay be !laced u!on the ter"inal and it will readilyrotate when the coil is o!erated by currents of very high fre5uency. ith a steady !otential, ofcourse, and even with alternating currents of very low fre5uency, it would not turn, because ofthe very slow echange of air and, conse5uently, s"aller bo"bard"ent( but in the latter caseit "ight turn if the !otential were ecessive. ith a !in wheel, 5uite the o!!osite rule holds

good( it rotates best with a steady !otential, and the effort is the s"aller the higher thefre5uency. =ow, it is very easy to ad3ust the conditions so that the !otential is nor"ally notsufficient to turn the fan, but that by connecting the other ter"inal of the coil with an insulated


22/57


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$o de"onstrate a novel and interesting feature, I have, for a reason which I will e!lain,selected this ty!e of "otor. hen the ends of the coil are connected to the ter"inals of analternator the disc is set in rotation. /ut it is not this e!eri"ent, now well #nown, which Idesire to !erfor". hat I wish to show you is that this "otor rotates with onesinleconnection between it and the generator( that is to say, one ter"inal of the "otor isconnected to one ter"inal of the generator&in this case the secondary of a high%tension

induction coil&the other ter"inals of "otor and generator being insulated in s!ace. $o!roduce rotation it is generally -but not absolutely necessary to connect the free end of the"otor coil to an insulated body of so"e si'e. $he e!eri"enter4s body is "ore thansufficient. If he touches the free ter"inal with an ob3ect held in the hand, a current !assesthrough the coil and the co!!er disc is set in rotation. If an ehausted tube is !ut in serieswith the coil, the tube lights brilliantly, showing the !assage of a strong current. Instead of thee!eri"enter4s body, a s"all "etal sheet sus!ended on a cord "ay be used with the sa"eresult. In this case the !late acts as a condenser in series with the coil. It counteracts theself%induction of the latter and allows a strong current to !ass. In such a co"bination, thegreater the self%induction of the coil the s"aller need be the !late, and this "eans that a lowerfre5uency, or eventually a lower !otential, is re5uired to o!erate the "otor. single coilwound u!on a core has a high self%induction( for this reason !rinci!ally, this ty!e of "otor waschosen to !erfor" the e!eri"ent. ere a secondary closed coil wound u!on the core, it

would tend to di"inish the self%induction, and then it would be necessary to e"!loy a "uchhigher fre5uency and !otential. =either would be advisable, for a higher !otential wouldendanger the insulation of the s"all !ri"ary coil, and a higher fre5uency would result in a"aterially di"inished tor5ue.

It should be re"ar#ed that when such a "otor with a closed secondary is used, it is not at alleasy to obtain rotation with ecessive fre5uencies, as the secondary cuts off al"ostco"!letely the lines of the !ri"ary&and this, of course, the "ore, the higher the fre5uency&and allows the !assage of but a "inute current. In such a case, unless the secondary isclosed through a condenser, it is al"ost essential, in order to !roduce rotation, to "a#e the!ri"ary and secondary coils overla! each other "ore or less.

/ut there is an additional feature of interest about this "otor, na"ely, it is not necessary to

have even a single connection between the "otor and generator, ece!t, !erha!s, throughthe ground( for not only is an insulated !late ca!able of giving off energy into s!ace, but it


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li#ewise ca!able of deriving it fro" an alternating electrostatic field, though in the latter casethe available energy is "uch s"aller. In this instance one of the "otor ter"inals is connectedto the insulated !late or body located within the alternating electrostatic field, and the otherter"inal !referably to the ground.

It is 5uite !ossible, however, that such Jno%wireJ "otors, as they "ight be called, could be

o!erated by conduction through the rarefied air at considerable distances. lternate currents,es!ecially of high fre5uencies, !ass with astonishing freedo" through even slightly rarefiedgases. $he u!!er strata of the air are rarefied. $o reach a nu"ber of "iles out into s!acere5uires the overco"ing of difficulties of a "erely "echanical nature. $here is no doubt thatwith the enor"ous !otentials obtainable by the use of high fre5uencies and oil insulation,lu"inous discharges "ight be !assed through "any "iles of rarefied air, and that, by thusdirecting the energy of "any hundreds or thousands of horse%!ower, "otors or la"!s "ightbe o!erated at considerable distances fro" stationary sources. /ut such sche"es are"entioned "erely as !ossibilities. e shall have no need to trans#it!ower at all. Ere "anygenerations !ass, our "achinery will be driven by a !ower obtainable at any !oint of theuniverse. $his idea is not novel. >en have been led to it long ago by instinct or reason( it hasbeen e!ressed in "any ways, and in "any !laces, in the history of old and new. e find itin the delightful "yth of ntheus @ntaeusB, who derives !ower fro" the earth( we find it

a"ong the subtle s!eculations of one of your s!lendid "athe"aticians and in "any hints andstate"ents of thin#ers of the !resent ti"e. $hroughout s!ace there is energy. Is this energystatic or #inetic; If static our ho!es are in vain( if #inetic&and this we #now it is, for certain&then it is a "ere 5uestion of ti"e when "en will succeed in attaching their "achinery to thevery wheelwor# of nature. f all, living or dead, *roo#es ca"e nearest to doing it. isradio"eter will turn in the light of day and in the dar#ness of the night( it will turn everywherewhere there is heat, and heat is everywhere. /ut, unfortunately, this beautiful little "achine,while it goes down to !osterity as the "ost interesting, "ust li#ewise be !ut on record as the"ost inefficient "achine ever invented+

$he !receding e!eri"ent is only one of "any e5ually interesting e!eri"ents which "ay be!erfor"ed by the use of only one wire with alternate currents of high !otential and fre5uency.e "ay connect an insulated line to a source of such currents, we "ay !ass anina!!reciable current over the line, and on any !oint of the sa"e we are able to obtain aheavy current, ca!able of fusing a thic# co!!er wire. r we "ay, by the hel! of so"e artifice,deco"!ose a solution in any electrolytic cell by connecting only one !ole of the cell to the lineor source of energy. r we "ay, by attaching to the line, or only bringing into its vicinity, lightu! an incandescent la"!, an ehausted tube, or a !hos!horescent bulb.

owever i"!racticable this !lan of wor#ing "ay a!!ear in "any cases, it certainly see"s!racticable, and even reco""endable, in the !roduction of light. !erfected la"! wouldre5uire but little energy, and if wires were used at all we ought to be able to su!!ly thatenergy without a return wire.

It is now a fact that a body "ay be rendered incandescent or !hos!horescent b bringing it

either in single contact or "erely in the vicinity of a source of electric i"!ulses of the !ro!ercharacter, and that in this "anner a 5uantity of light sufficient to afford a !ractical illu"inant"ay be !roduced. It is, therefore, to say the least, worth while to atte"!t to deter"ine thebest conditions and to invent the best a!!liances for attaining this ob3ect.

7o"e e!eriences have already been gained in this direction, and I will dwell on the" briefly,in the ho!e that they "ight !rove useful.

$he heating of a conducting body inclosed in a bulb, and connected to a source of ra!idlyalternating electric i"!ulses, is de!endent on so "any things of a different nature, that itwould be difficult to give a generally a!!licable rule under which this "ai"u" heatingoccurs. s regards the si'e of the vessel, I have lately found that at ordinary or only slightlydiffering at"os!heric !ressures, when air is a good insulator, and hence !ractically the sa"ea"ount of energy by a certain !otential and fre5uency is given off fro" the body, whether the
http://www.antaeus.org/antaeus/classic/Legend.htmlhttp://www.antaeus.org/antaeus/classic/Legend.html


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bulb be s"all or large, the body is brought to a higher te"!erature if inclosed in a s"all bulb,because of the better confine"ent of heat in this case.

t lower !ressures, when air beco"es "ore or less conducting, or if the air be sufficientlywar"ed as to beco"e conducting, the body is rendered "ore intensely incandescent in alarge bulb, obviously because, under otherwise e5ual conditions of test, "ore energy "ay be

given off fro" the body when the bulb is large.

t very high degrees of ehaustion, when the "atter in the bulb beco"es Jradiant,J a largebulb has still an advantage, but a co"!aratively slight one, over the s"all bulb. Finally, atecessively high degrees of ehaustion, which cannot be reached ece!t by the e"!loy"entof s!ecial "eans, there see"s to be, beyond a certain and rather s"all si'e of vessel, no!erce!tible difference in the heating.

$hese observations were the result of a nu"ber of e!eri"ents, of which one, showing theeffect of the si'e of the bulb at a high degree of ehaustion "ay be described and shownhere, as it !resents a feature of interest. $hree s!herical bulbs of 2 inches, C inches and inches dia"eter were ta#en, and in the centre of each was "ounted an e5ual length of an

ordinary incandescent la"! fila"ent of unifor" thic#ness. In each bulb the !iece of fila"entwas fastened to the leading%in wire of !latinu", contained in a glass ste" sealed in the bulb(care being ta#en, of course, to "a#e everything as nearly ali#e as !ossible. n each glassste" in the inside of the bulb was sli!!ed a highly !olished tube "ade of alu"iniu" sheet,which fitted the ste" and was held on it by s!ring !ressure. $he function of this alu"iniu"tube will be e!lained subse5uently. In each bulb an e5ual length of fila"ent !rotruded abovethe "etal tube. It is sufficient to say now that under these conditions e5ual lengths of fila"entof the sa"e thic#ness&in other words, bodies of e5ual bul#&were brought toincandescence. $he three bulbs were sealed to a glass tube, which was connected to a7!rengel !u"!. hen a high vacuu" had been reached, the glass tube carrying the bulbswas sealed off. current was then turned on successively on each bulb, and it was foundthat the fila"ents ca"e to about the sa"e brightness, and, if anything, the s"allest bulb,which was !laced "idway between the two larger ones, "ay have been slightly brighter. $his

result was e!ected, for when either of the bulbs was connected to the coil the lu"inositys!read through the other two, hence the three bulbs constituted really one vessel. hen allthe three bulbs were connected in "ulti!le arc to the coil, in the largest of the" the fila"entglowed brightest, in the net s"aller it was a little less bright, and in the s"allest it only ca"eto redness. $he bulbs were then sealed off and se!arately tried. $he brightness of thefila"ents was now such as "ould have been e!ected on the su!!osition that the energygiven off was !ro!ortionate to the surface of the bulb, this surface in each case re!resentingone of the coatings of a condenser. ccordingly, there was less difference between thelargest and the "iddle sited than between the latter and the s"allest bulb.

n interesting observation was "ade in this e!eri"ent. $he three bulbs were sus!endedfro" a straight bare wire connected to a ter"inal of the coil, the largest bulb being !laced atthe end of the wire, at so"e distance fro" it the s"allest bulb, and an e5ual distance fro" the

latter the "iddle%si'ed one. $he carbons glowed then to both the larger bulbs about ase!ected, but the s"allest did not get its share by far. $his observation led "e to echangethe !osition of the bulbs, and I then observed that whichever of the bulbs was in the "iddle itwas by far less bright than it was in any other !osition. $his "ystifying result was, of course,found to be due to the electrostatic action between the bulbs. hen they were !laced at aconsiderable distance, or when they were attached to the corners of an e5uilateral triangle ofco!!er wire, they glowed about in the order deter"ined by their surfaces.

s to the sha!e of the vessel, it is also of so"e i"!ortance, es!ecially at high degrees ofehaustion. f all the !ossible constructions, it see"s that a s!herical globe with therefractory body "ounted in its centre is the best to e"!loy. In e!erience it has beende"onstrated that in such a globe a refractory body of a given bul# is "ore easily brought toincandescence than when otherwise sha!ed bulbs are used. $here is also an advantage in

giving to the incandescent body the sha!e of a s!here, for self%evident reasons. In any casethe body should be "ounted in the centre, where the ato"s rebounding fro" the glass


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collide. $his ob3ect is best attained in the s!herical bulb( but it is also attained in a cylindricalvessel with one or two straight fila"ents coinciding with its ais, and !ossibly also in!arabolical or s!herical bulbs with the refractory body or bodies !laced in the focus or foci ofthe sa"e( though the latter is not !robable, as the electrified ato"s should in all casesrebound nor"ally fro" the surface they stri#e, unless the s!eed were ecessive, in whichcase they !o"ld!robably follow the general law of reflection. =o "atter what sha!e the

vessel "ay have, if the ehaustion be low, a fila"ent "ounted in the globe is brought to thesa"e degree of incandescence in all !arts( but if the ehaustion be high and the bulb bes!herical or !ear%sha!ed, as usual, focal !oints for" and the fila"ent is heated to a higherdegree at or near such !oints.

$o illustrate the effect, I have here two s"all bulbs which are ali#e, only one is ehausted to alow and the other to a very high degree. hen connected to the coil, the fila"ent in thefor"er glows unifor"ly throughout all its length( whereas in the latter, that !ortion of thefila"ent which is in the centre of the bulb glows far "ore intensely than the rest. curious!oint is that the !heno"enon occurs even if two fila"ent) are "ounted in a bulb, each beingconnected to one ter"inal of the coil, and, what is still "ore curious, if they be very neartogether, !rovided the vacuu" be very high. I noted in e!eri"ents with such bulbs that thefila"ents would give way usually at a certain !oint, and in the first trials I attributed it to a

defect in the carbon. /ut when that !heno"enon occurred "any ti"es in succession Irecogni'ed its real cause.

In order to bring a refractory body inclosed in a bulb to incandescence, it is desirable, onaccount of econo"y, that all the energy su!!lied to the bulb fro" the source should reachwithout lass the body to be heated( fro" there, and fro" nowhere else, it should be radiated.It is, of course, out of the 5uestion to reach this theoretical result, but it is !ossible by a !ro!erconstruction of the illu"inating device to a!!roi"ate it "ore or less.

For "any reasons, the refractory body is !laced in the centre of the bulb and it is usuallysu!!orted on a glass ste" containing the leading%in wire. s the !otential of this wire isalternated, the rarefied gas surrounding the ste" is acted u!on inductively, and the glass

ste" is violently bo"barded and heated. In this "anner by far the greater !ortion of theenergy su!!lied to the bulb&es!ecially when eceedingly high fre5uencies are used&"aybe lost for the !ur!ose conte"!lated. $o obviate this loss, or at least to reduce it to a"ini"u", I usually screen the rarefied gas surrounding the ste" fro" the inductive action ofthe leading%in wire by !roviding( the ste" with a tube or coating of conducting "aterial. Itsee"s beyond doubt that the best a"ong "etals to e"!loy for this !ur!ose is alu"iniu", onaccount of its "any re"ar#able !ro!erties. Its only fault is that it is easily fusible and,therefore, its distance fro" the incandescing) body should be !ro!erly esti"ated.


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that is, when the gas as a whole is non%conducting, and the "olecules, or ato"s, act asinde!endent carriers of electric charges.

In addition to acting as a "ore or less effective screen, in the true "eaning of the word, theconducting tube or coating "ay also act, by reason of its conductivity, as a sort of e5uali'er orda"!ener of the bo"bard"ent against the ste". $o be e!licit, I assu"e the action as

follows) 7u!!ose a rhyth"ical bo"bard"ent to occur against the conducting tube by reasonof its i"!erfect action as a screen, it certainly "ust ha!!en that so"e "olecules, or ato"s,stri#e the tube sooner than others. $hose which co"e first in contact with it give u! theirsu!erfluous charge, and the tube is electrified, the electrification instantly s!reading over itssurface. /ut this "ust di"inish, the energy lost in the bo"bard"ent for two reasons) first, thecharge given u! by the ato"s s!reads over a great area, and hence the electric density atany !oint is s"all, and the ato"s are rebelled with less energy than they would be if theywould stri#e against a good insulator( secondly, as the tube is electrified by the ato"s whichfirst co"e in contact with it, the !rogress of the following ato"s against the tube is "ore orless chec#ed by, the re!ulsion which the electrified tube "ust eert u!on the si"ilarlyelectrified ato"s. $his re!ulsion "ay !erha!s be sufficient to !revent a large !ortion of theato"s fro" stri#ing the tube, but at any rate it "ust di"inish the energy of their i"!act. It isclear that when the ehaustion is very low, and the rarefied gas well conducting, neither of the

above effects can occur, and, on the other hand, the fewer the ato"s, with the greaterfreedo" they "ove( in other words, the higher the degree of ehaustion, u! to a li"it, the"ore telling will be both the effects)

hat I have 3ust said "ay afford an e!lanation of the !heno"enon observed by 0rof.*roo#es, na"ely, that a discharge through a bulb is established with "uch greater facilitywhen an insulator than when a conductor is !resent in the sa"e. In "y o!inion, theconductor acts as a da"!ener of the "otion of the ato"s in the two ways !ointed out( hence,to cause a visible discharge to !ass through the bulb, a "uch higher !otential is needed if aconductor, es!ecially of "any surfaces, be !resent.

For the sa#e of clearness of so"e of the re"ar#s before "ade, I "ust now refer to Figs. 18,19, and 2?, which illustrate various arrange"ents with a ty!e of bulb "ost generally used.

Fig. 18 is a section though a s!herical bulb L, with the glass ste" s, containing the leading%inwire !, which has a la"! fila"ent lfastened to it, serving to su!!ort the refractory button #in


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the centre. > is a sheet of thin "ica wound in several layers around the ste" s, and ais thealu"iniu" tube.

Fig. 19 illustrates such a bulb in a so"ewhat "ore advanced stage of !erfection. "etallictube 7 is fastened by "eans of so"e ce"ent to the nec# of the tube. In the tube is screweda !lug 0, of insulating "aterial, in the centre of which is fastened a "etallic ter"inal t, for the

connection to the lead%in wire !. $his ter"inal "ust be well insulated fro" the "etal tube 7,therefore, if the ce"ent used is conducting and "ost generally it is sufficiently so&the s!acebetween the !lug 0 and the nec# of the bulb should be filled with so"e good insulating"aterial, as "ica !owder.

Fig. 2? shows a bulb "ade for e!eri"ental !ur!oses. In this bulb the alu"iniu" tube is!rovided with an eternal connection, which serves to investigate the effect of the tube undervarious conditions. It is referred to chiefly to suggest a line of e!eri"ent followed.

7ince the bo"bard"ent against the ste" containing the leading%in wire is due to the inductiveaction of the latter u!on the rarefied gas, it is of advantage to reduce this action as far as!racticable by e"!loying a very thin wire, surrounded by a very thic# insulation of glass orother "aterial, and by "a#ing the wire !assing through the rarefied gas as short as!racticable. $o co"bine these features I e"!loy a large tube $ -Fig. 21, which !rotrudes intothe bulb to so"e distance, and carries on the to! a very short glass ste" s, into which issealed the leading%in wire !, and I !rotect the to! of the glass ste" against the heat by as"all, alu"iniu" tube aand a layer of "ica underneath the sa"e, as usual. $he wire !,!assing through the large tube to the outside of the bulb, should be well insulated&with aglass tube, for instance&and the s!ace between ought to be filled out with so"e ecellentinsulator. "ong "any insulating !owders I have tried, I have found that "ica !owder is thebest to e"!loy. If this !recaution is not ta#en, the tube $, !rotruding into the bulb, will surelybe crac#ed in conse5uence of the heating by the brushes which are a!t to for" in the u!!er!art of the tube, near the ehausted globe, es!ecially if the vacuu" be ecellent, andtherefore the !otential necessary to o!erate the la"! be very high.


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Fig. 22 illustrates a si"ilar arrange"ent, with a large tube $ !rotruding into the !art of the bulbcontaining the refractory button #. In this case the wire leading fro" the outside into the bulbis o"itted, the energy re5uired being su!!lied through condenser coatings * *. $heinsulating !ac#ing 0 should in this construction be tightly fitting to the glass, and rather wide,or otherwise the discharge "ight avoid !assing through the wire !, which connects the insidecondenser coating to the incandescent button #.

$he "olecular bo"bard"ent against the glass ste" in the bulb is a source of great trouble.s illustration I will cite a !heno"enon only too fre5uently and unwillingly observed. bulb,

!referably a large one, "ay be ta#en, and a good conducting body, such as a !iece ofcarbon, "ay be "ounted in it u!on a !latinu" wire sealed in the glass ste". $he bulb "aybe ehausted to a fairly high degree, nearly to the !oint when !hos!horescence begins toa!!ear. hen the bulb is connected with the coil, the !iece of carbon, if s"all, "ay beco"ehighly incandescent at first, but its brightness i""ediately di"inishes, and then the discharge"ay brea# through the glass so"ewhere in the "iddle of the ste", in the for" of brights!ar#s, in s!ite of the fact that the !latinu" wire is in good electrical connection with therarefied gas through the !iece of carbon or "etal at the to!. $he first s!ar#s are singularlybright, recalling those drawn fro" a clear surface of "ercury. /ut, as they heat the glassra!idly, they, of course, lose their brightness, and cease when the glass at the ru!tured !lacebeco"es incandescent, or generally sufficiently hot to conduct. hen observed for the firstti"e the !heno"enon "ust a!!ear very curious, and shows in a stri#ing "anner howradically different alternate currents, or i"!ulses, of high fre5uency behave, as co"!ared with

steady currents, or currents of low fre5uency. ith such currents&na"ely, the latter&the!heno"enon would of course not occur. hen fre5uencies such as are obtained by"echanical "eans are used, I thin# that the ru!ture of the glass is "ore or less theconse5uence of the bo"bard"ent, which war"s it u! and i"!airs its insulating !ower( butwith fre5uencies obtainable with condensers I have no doubt that the glass "ay give waywithout !revious heating. lthough this a!!ears "ost singular at first, it is in reality what we"ight e!ect to occur. $he energy su!!lied to the wire leading into the bulb is given off !artlyby direct action through the carbon button, and !arty by inductive action through the glasssurrounding the wire. $he case is thus analogous to that in which a condenser shunted by aconductor of low resistance is connected to a source of alternating currents. s long as thefre5uencies are low, the conductor gets the "ost, and the condenser is !erfectly safe( butwhen the fre5uency beco"es ecessive, the roleof the conductor "ay beco"e 5uiteinsignificant. In the latter case the difference of !otential at the ter"inals of the condenser

"ay beco"e so great as to ru!ture the dielectric, notwithstanding the fact that the ter"inalsare 3oined by a conductor of low resistance.


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It is, of course, not necessary, when it is desired to !roduce the incandescence of a bodyinclosed in a bulb by "eans of these currents, that the body should be a conductor, for even a!erfect non%conductor "ay be 5uite as readily heated. For this !ur!ose it is sufficient tosurround a conducting electrode with a non%conducting "aterial, as, for instance, in the bulbdescribed before in Fig. 21, in which a thin incandescent la"! fila"ent is coated with a non%conductor, and su!!orts a button of the sa"e "aterial on the to!. t the start the

bo"bard"ent goes on by inductive action through the non%conductor, until the sa"e issufficiently heated to beco"e conducting, then the bo"bard"ent continues in the ordinaryway.

different arrange"ent used in so"e of the bulbs constructed is illustrated in Fig. 2C. In thisinstance a non%conductor #is "ounted in a !iece of co""on arc light carbon so as to !ro3ectso"e s"all distance above the latter. $he carbon !iece is connected to the leading%in wire!assing through a glass ste", which is wra!!ed with several layers of "ica. n alu"iniu"tube a is e"!loyed as usual for screening. It is so arranged that it reaches very nearly ashigh as the carbon and only the non%conductor " !ro3ects a little above it. $he bo"bard"entgoes at first against the u!!er surface of carbon, the lower !arts being !rotected by thealu"iniu" tube. s soon, however, as the non%conductor " is heated it is rendered goodconducting, and then it beco"es the centre of the bo"bard"ent, being "ost e!osed to the

sa"e.

I have also constructed during these e!eri"ents "any such single%wire bulbs with or withoutinternal electrode, in which the radiant "atter was !ro3ected against, or focused u!on, thebody to be rendered incandescent. Fig. 2 illustrates one of the bulbs used. It consists of as!herical globe L, !rovided with a long nec# n, on the to!, for increasing the action in so"ecases by the a!!lication of an eternal conducting coating. $he globe L is blown out on thebotto" into a very s"all bulb b, which serves to hold it fir"ly in a soc#et 7 of insulating"aterial into which it is ce"ented. fine la"! fila"ent f, su!!orted on a wire !, !assesthrough the centre of fila"ent is rendered incandescent In the "iddle !ortion, where thebo"bard"ent !roceeding fro" the lower inside surface of the globe is "ost intense. $helower !ortion of the globe, as far as the soc#et 7 reaches, is rendered conducting, either by gtinfoil coating or otherwise, and the eternal electrode is connected to a ter"inal of the coil.


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$he arrange"ent diagra""atically indicated in Fig. 2 was found to be an inferior one whenit was desired to render incandescent a fila"ent or button su!!orted in the centre of theglobe, but it was convenient when the ob3ect was to ecite !hos!horescence.

In "any e!eri"ents in which bodies of a different #ind were "ounted in the bulb as, forinstance, indicated in Fig. 2C, so"e observations of interest were "ade.

It was found, a"ong other things, that in such cases, no "atter where the bo"bard"entbegan, 3ust as soon as a high te"!erature was reached there was generally one of the bodieswhich see"ed to ta#e "ost of the bo"bard"ent u!on itself, the other, or others, beingthereby relieved. $his 5uality a!!eared to de!end !rinci!ally on the !oint of fusion, and on thefacility with which the body was Jeva!orated,J or, generally s!ea#ing, disintegrated&"eaningby the latter ter" not only the throwing off of ato"s, but li#ewise of larger lu"!s. $heobservation "ade was in accordance with generally acce!ted notions. In a highly ehaustedbulb electricity is carried off fro" the electrode by inde!endent carriers, which are !artly theato"s, or "olecules, of the residual at"os!here, and !artly the ato"s, "olecules, or lu"!sthrown off fro" the electrode. If the electrode is co"!osed of bodies of different character,and if one of these is "ore easily disintegrated than the others, "ost of the electricity su!!liedis carried off fro" that body, which is then brought to a higher te"!erature than the others,and this the "ore, as u!on an increase of the te"!erature the body is still "ore easilydisintegrated.

It see"s to "e 5uite !robable that a si"ilar !rocess ta#es !lace in the bulb even with aho"ogenous electrode, and I thin# it to be the !rinci!al cause of the disintegration. $here isbound to be so"e irregularity, even if the surface is highly !olished, which, of course, isi"!ossible with "ost of the refractory bodies e"!loyed as electrodes. ssu"e that a !oint ofthe electrode gets hotter, instantly "ost of the discharge !asses through that !oint, and a"inute !atch is !robably fused and eva!orated. It is now !ossible that in conse5uence of theviolent disintegration the s!ot attac#ed sin#s in te"!erature, or that a counter force is created,as in an arc( at any rate, the local tearing off "eets with the li"itations incident to thee!eri"ent, where u!on the sa"e !rocess occurs on another !lace. $o the eye the electrode

a!!ears unifor"ly brilliant, but there are u!on it !oints constantly shifting and wanderingaround, of a te"!erature far above the "ean, and this "aterially hastens the !rocess ofdeterioration. $hat so"e such thing occurs, at least when the electrode is at a lowerte"!erature, sufficient e!eri"ental evidence can be obtained in the following "anner)Ehaust a bulb to a very high degree, so that with a fairly high !otential the discharge cannot!ass&that is, not a l"#ino"sone, for a wea# invisible discharge occurs always, in all!robability. =ow raise slowly and carefully the !otential, leaving the !ri"ary current on no"ote than for an instant. t a certain !oint, two, three, or half a do'en !hos!horescent s!ots"ill a!!ear on the globe. $hese !laces of the glass are evidently "ore violently bo"bardedthan others, this being due to the unevenly distributed electric density, necessitated, ofcourse, by shar! !ro3ections, or, generally s!ea#ing, irregularities of the electrode. /ut thelu"inous !atches are constantly changing in !osition, which is es!ecially well observable ifone "anages to !roduce very few, and this indicates that the configuration of the electrode is

ra!idly changing.

Fro" e!eriences of this #ind I a" led to infer that, in order to be "ost durable, the refractorybutton in the bulb should be in the for" of a s!here with a highly !olished surface. 7uch as"all s!here could be "anufactured fro" a dia"ond or so"e other crystal, but a better waywould be to fuse, by the e"!loy"ent of etre"e degrees of te"!erature, so"e oide&as, forinstance, 'irconia&into a s"all dro!, and then #ee! it in the bulb at a te"!erature so"ewhatbelow its !oint of fusion.

Interesting and useful results can no doubt be reached in the direction of etre"e degrees ofheat. ow can such high te"!eratures be arrived at; ow are the highest degrees of heatreached in nature; /y the i"!act of stars, by high s!eeds and collisions. In a collision anyrate of heat generation "ay be attained. In a che"ical !rocess we are li"ited. hen oygen

and hydrogen co"bine, they fall, "eta!horically s!ea#ing, fro" a definite height. e cannotgo very far with a blast, nor by confining heat in a furnace, but in an ehausted bulb we can


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concentrate any a"ount of energy u!on a "inute button. Leaving !racticability out ofconsideration, this, then, would be the "eans which, in "y o!inion, would enable us to reachthe highest te"!erature. /ut a great difficulty when !roceeding in this way is encountered,na"ely, in "ost cases the body is carried off before it can fuse and for" a dro!. $his difficultyeists !rinci!ally with an oide such as 'irconia, because it cannot be co"!ressed in so harda ca#e that it would not be carried off 5uic#ly. I endeavored re!eatedly to fuse 'irconia,

!lacing it in a cu! or arc light carbon as indicated in Fig. 2C. It glowed with a "ost intenselight, and the strea" of the !articles !ro3ected out of the carbon cu! was of a vivid white( butwhether it was co"!ressed in a ca#e or "ade into a !aste with carbon, it was carried offbefore it could be fused. $he carbon cu! containing the 'irconia had to be "ounted very lowin the nec# of a large bulb, as the heating of the glass by the !ro3ected !articles of the oidewas so ra!id that in the first trial the bulb was crac#ed al"ost in an instant when the currentwas turned on. $he heating of the glass by the !ro3ected !articles was found to be alwaysgreater when the carbon cu! contained a body which was ra!idly carried off&I !resu"ebecause in such cases, with the sa"e !otential, higher s!eeds were reached, and alsobecause, !er unit of ti"e, "ore "atter was !ro3ected&

experiments with alternate currents of high potential and high frequency

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