8/12/2019 On the Dissipation of the Electrical Energy of the Hertz Resonator

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The Electrical Engineer December 21, 1892

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Anyone who, like myself, has had the pleasure of witnessing the beautiful demonstrations

with vibrating diaphragms which Prof !"erknes, e#hibited in person at the Paris $#position in188%, must have admired his ability and painstaking care to such a degree, as to have analmost implicit faith in the correctness of observations made by him &is e#periments '(n theDissipation of the $lectrical $nergy of the &ert) *esonator,' which are described in the issueof Dec 1+, of &$ $-$.*/.0- $/$$*, are prepared in the same ingenious and skillfulmanner, and the conclusions drawn from them are all the more interesting as they agree withthe theories put forth by the most advanced thinkers here can not be the slightest doubt asto the truth of these conclusions, yet the statements which follow may serve to e#plain in partthe results arrived at in a different manner3 and with this ob"ect in view / venture to callattention to a condition with which, in investigations such as those of Prof !"erknes, thee#perimenter is confronted

he apparatus, oscillator and resonator, being immersed in air, or other discontinuous

medium, there occursas / have pointed out in the description of my recent e#perimentsbefore the $nglish and 4rench scientific societiesdissipation of energy by what / think mightbe appropriately called electric sound wavesor sound-waves of electrified air /n Prof!"erknes5s e#periments principally this dissipation in the resonator need be considered,though the sound6wavesif this term be permittedwhich emanate from the surfaces at theoscillator may considerably affect the observations made at some distance from the latter(wing to this dissipation the period of vibration of an air6condenser can not be accuratelydetermined, and / have already drawn attention to this important fact hese waves arepropagated at right angles from the charged surfaces when their charges are alternated, anddissipation occurs, even if the surfaces are covered with thick and e#cellent insulation0ssuming that the 'charge' imparted to a molecule or atom either by direct contact orinductively is proportionate to the electric density of the surface, the dissipation should beproportionate to the s7uare of the density and to the number of waves per second he

above assumption, it should be stated, does not agree with some observations from which itappears that an atom can not take but a certain ma#imum charge3 hence, the chargeimparted may be practically independent of the density of the surface, but this is immaterialfor the present consideration his and other points will be decided when accurate7uantitative determinations, which are as yet wanting, shall be trade 0t present it appearscertain from e#periments with, high6fre7uency currents, that this dissipation of energy from awire, for instance, is not very far from being proportionate to the fre7uency of the alternations,and increases very rapidly when the diameter of the wire is made e#ceedingly small (n thelatter point the recently published results of Prof 0yrton and & ilgour on 'he hermal$missivity of hin ires in 0ir' throw a curious light $#ceedingly thin wires are capable ofdissipating a comparatively very great amount of energy by the agitation of the surroundingair, when they are connected to a source of rapidly alternating potential :o in the e#perimentcited, a thin hot wire is found to be capable of emitting an e#traordinarily great amount of

heat, especially at elevated temperatures /n the case of a hot wire it must of course beassumed that the increased emissivity is due to the more rapid convection and not, to any,appreciable degree, to an increased radiation ere the latter demonstrated, it would showthat a wire, made hot by the application of heat in ordinary ways, behaves in some respectslike one, the charge of which is rapidly alternated, the dissipation of energy per unit of surfacekept at a certain temperature depending on the curvature of the surface / do not recall anyrecord of e#periments intended to demonstrate this, yet this effect, though probably verysmall, should certainly be, looked for

0 number of observations showing the peculiarity, of very thin wires were made in the courseof my e#periments / noted, for instance, that in the well6known .rookes instrument the micavanes are repelled with comparatively greater force when the incandescent platinum wire ise#ceedingly thin his observation enabled me to produce the spin of such vanes mounted ina vacuum tube when the latter was placed in an alternating electrostatic field his however

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does not prove anything in regard to radiation, as in a highly e#hausted vessel tilephenomena are principally due to molecular bombardment or convection

hen / first undertook to produce the incandescence of a wire enclosed in a bulb, byconnecting it to only oneof the terminals of a high tension transformer, / could not succeed fora long time (n one occasion / had mounted in a bulb a thin platinum wire, but my apparatus

was not ade7uate to produce the incandescence / made other bulbs, reducing the length ofthe wire to a small fraction3 still / did not succeed /t then occurred to me that it would bedesirable to have the surface of the wire as large as possible, yet the bulk small, and /provided a bulb with an e#ceedingly thin wire of a bulk about e7ual to that of the short butmuch thicker wire (n turning the current on the bulb the wire was instantly fused 0 series ofsubse7uent e#periments showed that when the diameter of the wire was e#ceedingly small,considerably more energy would be dissipated per unit surface at all degrees of e#haustionthan was to be e#pected, even on the assumption that the energy given off was in proportionto the s7uare of the electric density here is likewise evidence which, though not possessingthe certainty of an accurate 7uantitative determination, is nevertheless reliable because it isthe result of a great many observations, namely, that with the increase of the density thedissipation is more rapid for thin than for thick wires

he effects noted in e#hausted vessels with high6fre7uency currents are merely diminished indegree when the air is at ordinary pressure, but heating and dissipation occurs, as / havedemonstrated, under the ordinary atmospheric conditions wo very thin wires attached to theterminals of a high6fre7uency coil are capable of giving off an appreciable amount of energyhen the density is very great, the temperature of the wires may be perceptibly raised, and insuch case probably the greater portion of the energy which is dissipatedowing to thepresence of a discontinuous mediumis transformed into heat at the surface or in closepro#imity to the wires :uch heating could not occur in a medium possessing either of the two7ualities, namely, perfect incompressibility or perfect elasticity /n fluid insulators, such as oils,though they are far from being perfectly incompressible or elastic to electric displacement, theheating is much smaller because of the continuity of the fluid

hen the electric density of the wire surfaces is small, there is no appreciable local heating,nevertheless energy is dissipated in air, by waves, which differ from ordinary sound6wavesonly because the air is electrified hese waves are especially conspicuous when thedischarges of a powerful battery are directed through a short and thick metal bar, the numberof discharges per second being very small he e#perimenter may feel the impact of the airat distances of si# feet or more from the bar, especially if be takes the precaution to sprinklethe face or hands with ether hese waves cannot be entirely stopped by the interposition ofan insulated metal plate

;ost of the striking phenomena of mechanical displacement, sound, heat and light whichhave been observed, imply the presence of a medium of a gaseous structure that is oneconsisting of independent carriers capable of free motion

hen a glass plate is placed near a condenser the charge of which is alternated, the plateemits a sound his sound is due to the rhythmical impact of the air against the plate / havealso found that the ringing of a condenser, first noted by :ir illiam homson, is due to thepresence of the air between or near the charged surfaces

hen a disruptive discharge coil is immersed in oil contained in a tank, it is observed that thesurface of the oil is agitated his may be thought to be due to the displacements produced inthe oil by the changing stresses, but such is not the case /t is the air above the oil which isagitated and causes the motion of the latter3 the oil itself would remain at rest hedisplacements produced in it by changing electrostatic stresses are insignificant3 to suchstresses it may be said to be compressible to but a very small degree he action of the air isshown in a curious manner for if a pointed metal bar is taken in the hand and held with thepoint close to the oil, a hole two inches deep is formed in the oil by the molecules of the air,which are violently pro"ected from the point

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he preceding statements may have a general bearing upon investigations in which currentsof high fre7uency and potential are made use of, but they also have a more direct bearingupon the e#periments of Prof !"erknes which are here considered, namely, the 'skin effect,'is increased by the action of the air /magine a wire immersed in a medium, the conductivityof which would be some function of the fre7uency and potential difference but such, that theconductivity increases when either or bout of these elements are increased /n such a

medium, the higher the fre7uency and potential difference, the greater wilt be the currentwhich will find its way through the surrounding medium, and the smaller the part which willpass through the central portion of the wire< /n the case of a wire immersed in air andtraversed by a high6fre7uency current, the facility with which the energy is dissipated may beconsidered as the e7uivalent of the conductivity3 and the analogy would be 7uite complete,were it not that besides the air another medium is present, the total dissipation being merelymodified by the presence of the air to an e#tent as yet not ascertained evertheless, / havesufficient evidence to draw the conclusion, that the results obtained by Prof !"erknes areaffected by the presence of air in the following manner< 1 he dissipation of energy is morerapid when the resonator is immersed in air than it would be in a practically continuousmedium, for instance, oil 2 he dissipation owing to the presence of air renders thedifference between magnetic and non6magnetic metals more striking he first conclusionfollows directly from the preceding remarks3 the second follows front the two facts that the

resonator receives always the same amount of energy, independent of the nature of themetal, and that the magnetism of the metal increases the impedance of the circuit 0resonator of magnetic metal behaves virtually as though its circuit were longer here is agreater potential difference set up per unit of length3 although this rosy not show itself in thedeflection of the electrometer owing to the lateral dissipation he effect of the increasedimpedance is strikingly illustrated in the two e#periments of Prof !"erknes when copper isdeposited upon an iron wire, and ne#t iron upon a copper wire .onsiderable thickness ofcopper deposit was re7uired in the former e#periment, but very little thickness of iron in thelatter, as should be e#pected

aking the above views, / believe, that in the e#periments of Prof !"erknes which lead him toundoubtedly correct conclusions, the air is a factor fully as important, if not more so, than theresistance of the metals