Experiments with Alternate Currents of High Potential and High Frequency (1892) — part 6 of 8

It can be a condenser, storing and returning the energy supplied to it, or it can be a mere sink of energy, and the conditions of the experiment determine whether it is more one or the other. The sphere being charged to a high po¬ tential, it acts inductively upon the surrounding air, or whatever gaseous medium there might be. The mole¬ cules, or atoms, which are near the sphere are of course more attracted, and move through a greater distance than the farther ones. When the nearest molecules strike the sphere they are repelled, and collisions occur at all distances within the inductive action of the sphere. It is now clear that, if the potential be steady, but little loss of energy can be caused in this way, for the molecules which are nearest to the sphere, having had an additional charge imparted to them by contact, are not attracted until they have parted, if not with all, at least with most of the additional charge, which can be accomplished only after a great many collisions. From the fact that with a steady potential there is but little loss in dry air, one must come to such a conclusion. When the potential of the sphere, instead of being steady, is alter¬ nating, the conditions are entirely different. In this case a rhythmical bombardment occurs, no matter whether the molecules after coming in contact with the sphere lose the imparted charge or not; what is more, if the charge is not lost, the impacts are only the more violent. Still if the frequency of the impulses be very small, the loss caused by the impacts and collisions would not be serious unless the potential were excessive. But when extremely high frequen¬ cies and more or less high potentials are used, the loss may be very great. The total energy lost per unit of time is propor-

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tionate to the product of the number of impacts per second, or the frequency and the energy lost in each impact. But the energy of an impact must be proportionate to the square of the electric density of the sphere, since the charge im¬ parted to the molecule is proportionate to that density. I conclude from this that the total energy lost must be propor¬ tionate to the product of the frequency and the square of the electric density ; but this law needs experimental con¬ firmation. Assuming the preceding considerations to be true, then, by rapidly alternating the potential of a body im¬ mersed in an insulating gaseous medium, any amount of energy may be dissipated into space. Most of that energy then, I believe, is not dissipated in the form of long ether waves, propagated to considerable distance, as is thought most generally, but is consumed — in the case of an insulated sphere, for example — in impact and collisional losses — that is, heat vibrations — on the surface and in the vicinity of the sphere. To reduce the dissipation it is necessary to work with a small electric density— the smaller the higher the frequency.

But since, on the assumption before made, the loss is diminished with the square of the density, and since cur¬ rents of very high frequencies involve considerable waste when transmitted through conductors, it follows that, on the whole, it is better to employ one wire than two. Therefore, if motors, lamps, or devices of any kind are perfected, capable of being advantageously operated by currents of extremely high frequency, economical reasons will make it advisable to use only one wire, especially if the distances are great.

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Wlien energy is absorbed in a condenser the same be¬ haves as though its capacity were increased. Absorption always exists more or less, but generally it is small and of no consequence as long as the frequencies are not very great. In using extremely high frequencies, and, neces¬ sarily in such case, also high potentials, the absorption — or, what is here meant more particularly by this term, the loss of energy due to the presence of a gaseous medium — is an important factor to be considered, as the energy absorbed in the air condenser may be any fraction of the supplied energy. This would seem to make it very difficult to tell from the measured or computed capacity of an air condenser its actual capacity or vibration period, especially if the con¬ denser is of very small surface and is charged to a very high potential. As many important results are dependent upon the correctness of the estimation of the vibration period, this subject demands the most careful scrutiny of other in¬ vestigators. To reduce the probable error as much as possible in experiments of the kind alluded to, it is advisable to use spheres or plates of large surface, so as to make the density exceedingly small. Otherwise, when it is practicable, an oil condenser should be used in preference. In oil or other liquid dielectrics there are seemingly no such losses as in gaseous media. It being impossible to exclude entirely the gas in condensers with solid dielectrics, such condensers should be immersed in oil, for economical reasons if nothing else; they can then be strained to the utmost and will remain cool. In Leyden jars the loss due to air is comparatively small, as the tin- foil coatings are large, close together, and the charged

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surfaces not directly exposed; but when the potentials are very high, the loss may be more or less considerable at, or near, the upper edge of the foil, where the air is princi¬ pally acted upon. If the jar be immersed in boiled-out oil, it will be capable of performing four times the amount of work which it can for any length of time when used in the ordinary way, and the loss will be inappreciable.

It should not be thought that the loss in heat in an air condenser is necessarily associated with the formation of visible streams or brushes. If a small electrode, inclosed in an unexhausted bulb, is connected to one of the ter¬ minals of the coil, streams can be seen to issue from the electrode and the air in the bulb is heated; if, instead of a small electrode, a large sphere is inclosed in the bulb, no streams are observed, still the air is heated.

Nor should it be thought that the temperature of an air condenser would give even an approximate idea of the loss in heat incurred, as in such case heat must be given off much more quickly, since there is, in addition to the ordinary radiation, a very active carrying away of heat by independent carriers going on, and since not only the ap¬ paratus, but the air at some distance from it is heated in consequence of the collisions which must occur.

Owing to this, in experiments with such a coil, a rise of temperature can be distinctly observed only when the body connected to the coil is very small. But with apparatus on a larger scale, even a body of considerable bulk would be heated, as, for instance, the body of a person ; and I think that skilled physicians might make observations of utility in such experiments, which, if the apparatus were

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judiciously designed, would not present the slightest danger.

A question of some interest, principally to meteorologists, presents itself here. How does the earth behave ? The earth is an air condenser, but is it a perfect or a very im¬ perfect one — a mere sink of energy ? There can be little doubt that to such small disturbance as might, be caused in an experiment the earth behaves as an almost perfect con¬ denser. But it might be different when its charge is set in vibration by some sudden disturbance occurring in the heavens. In such case, as before stated, probably only little of the energy of the vibrations set up would be lost into space in the form of long ether radiations, but most of the energy, I think, would spend itself in molecular im¬ pacts and collisions, and pass off into space in the form of short heat, and possibly light, waves. As both the fre¬ quency of the vibrations of the charge and the potential are in all probability excessive, the energy converted into heat may be considerable. Since the density must be unevenly distributed, either in consequence of the irregularity of the earth’s surface, or on account of the condition of the at¬ mosphere in various places, the effect produced would ac¬ cordingly vary from place to place. Considerable varia¬ tions in the temperature and pressure of the atmosphere may in this manner be caused at any point of the surface of the earth. The variations may be gradual or very sud¬ den, according to the nature of the general disturbance, and may produce rain and storms, or locally modify the weather in any way.

From the remarks before made one may see what an im-

110

portant factor of loss the air in tlie neighborhood of a

charged surface becomes when the electric density is great

and the frequency of the impulses excessive. But the

action as explained implies that the air is insulating — that

is, that it is composed of independent carriers immersed in

an insulating medium. This is the case only when the air

is at something like ordinary or greater, or at extremely

small, pressure. When the air is slightly rarefied and con

ducting, then true conduction losses occur also. In such case,

of course, considerable energy may be dissipated into space

\

even with a steady potential, or with impulses of low fre¬ quency, if the density is very great.

When the gas is at very low pressure, an electrode is heated more because higher speeds can be reached. If the gas around the electrode is strongly compressed, the dis¬ placements, and consequently the speeds, are very small, and the heating is insignificant. But if in such case the frequency could be sufficiently increased, the electrode would be brought to a high temperature as well as if the gas were at very low pressure; in fact, exhausting the bulb is only necessary because we cannot produce (and possibly not convey) currents of the required frequency.

Returning to the subject of electrode lamps, it is ob¬ viously of advantage in such a lamp to confine as much as possible the heat to the electrode by preventing the circula¬ tion of the gas in the bulb. If a very small bulb be taken, it would confine the heat better than a large one, but it might not be of sufficient capacity to be operated from the coil, or, if so, the glass might get too hot. A simple way to improve in this direction is to employ a globe of the re-

Ill

quired size, but to place a small bulb, the diameter of which is properly estimated, over the refractory button contained in the globe. This arrangement is illustrated in Fig. 28. The globe L has in this case a large neck n, allowing

Fig. 28.— Lamp with Auxiliary Bulb for Confining the

Action to the Centre.

the small bulb 6 to slip through. Otherwise the construc¬ tion is the same as shown in Fig. 18, for example. The small bulb is conveniently supported upon the stem s, car-

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rying the refractory button m. It is separated from the aluminium tube a by several layers of mica M, in order to prevent the cracking of the neck by the rapid heating of the aluminium tube upon a sudden turning on of the cur¬ rent. The inside bulb should be as small as possible when it is desired to obtain light only by incandescence of the electrode. If it is desired to produce phosphorescence, the bulb should be larger, else it would be apt to get too hot, and the phosphorescence would cease. In this arrange¬ ment usually only the small bulb shows phosphorescence, as there is practically no bombardment against the outer globe. In some of these bulbs constructed as illustrated in Fig. 28 the small tube was coated with phosphorescent paint, and beautiful effects were obtained. Instead of mak- ' ing the inside bulb large, in order to avoid undue heating, it answers the purpose to make the electrode m larger. In this case the bombardment is weakened by reason of the smaller electric density.

Many bulbs were constructed on the plan illustrated in Fig. 29. Here a small bulb b, containing the refractory button vi, upon being exhausted to a very high degree was sealed in a large globe L, which was then moderately ex¬ hausted and sealed off. The principal advantage of this con¬ struction was that it allowed of reaching extremely high vacua, and, at the same time use a large bulb. It was found, in the course of experiences with bulbs such as illustrated in Fig. 29, that it was well to make the stem s near the seal at e very thick, and the leading-in wire w thin, as it oc¬ curred sometimes that the stem at e was heated and the bulb was cracked, Often the outer globe L was exhausted

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only just enough to allow the discharge to pass through, and the space between the bulbs appeared crimson, pro ducing a curious effect. In some cases, when the exhaus¬ tion in globe L was very low, and the air good conducting, it was found necessary, in order to bring the button m to

Fig. 29.— Lamp with Independent Auxiliary Bulb.

high incandescence, to place, preferably on the upper part of the neck of the globe, a tinfoil coating which was con¬ nected to an insulated body, to the ground, or to the other terminal of the coil, as the highly conducting air weak-

114

ened the effect somewhat, probably by being acted upon inductively from the wire w, where it entered the bulb at e. Another difficulty — which, however, is always present when the refractory button is mounted in a very small bulb — existed in the construction illustrated in Fig. 29, namely, the vacuum in the bulb b would be impaired in a com¬ paratively short time.

The chief idea in the two last described constructions was to confine the heat to the central portion of the globe by preventing the exchange of air. An advantage is secured, but owing to the heating of the inside bulb and slow evap¬ oration of the glass the vacuum is hard to maintain, even if the construction illustrated in Fig. 28 be chosen, in which both bulbs communicate.

But by far the better way — the ideal way— would be to reach sufficiently high frequencies. The higher the frequency the slower would be the exchange of the air, and I think that a frequency may be reached at which there would be no exchange whatever of the air molecules around the ter¬ minal. We would then produce a flame in which there would be no carrying away of material, and a queer flame’ it would be, for it would be rigid ! With such high fre¬ quencies the inertia of the particles would come into play. As the brush, or flame, would gain rigidity in virtue of the inertia of the particles, the exchange of the latter would be prevented. This would necessarily occur, for, the num¬ ber of the impulses being augmented, the potential energy of each would diminish, so that finally only atomic vibra¬ tions could be set up, and the motion of translation through measurable space would cease. Thus an ordinary gas burner

115

connected to a source of rapidly alternating potential might have its efficiency augmented to a certain limit, and this for two reasons — because of the additional vibration imparted, and because of a slowing down of the process of carrying off. But the renewal being rendered difficult, and renewal being necessary to maintain the burner, a continued in¬ crease of the frequency of the impulses, assuming they could be transmitted to and impressed upon the flame, would result in the “ extinction ” of the latter, meaning by this term only the cessation of the chemical process.

I think, however, that in the case of an electrode im¬ mersed in a fluid insulating medium, and surrounded by independent carriers of electric charges, which can be acted upon inductively, a sufficiently high frequency of the im¬ pulses would probably result in a gravitation of the gas all around toward the electrode. For this it would be only necessary to assume that the independent bodies are irregularly shaped; they would then turn toward the elec¬ trode their side of the greatest electric density, and this would be a position in which the fluid resistance to ap¬ proach would be smaller than that offered to the receding.

The general opinion, I do not doubt, is that it is out of the question to reach any such frequencies as might — assuming some of the views before expressed to be true — produce any of the results which 1 have pointed out as mere possibilities. This may be so, but in the course of these investigations, from the observation of many phenomena I have gained the conviction that these frequencies would be much lower than one is apt to estimate at first. In a flame we set up light vibrations by causing molecules, or atoms, to collide.

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But wliat is the ratio of the frequency of the collisions and that of the vibrations set up ? Certainly it must be incom¬ parably smaller than that of the knocks of the bell and the sound vibrations, or that of the discharges and the oscilla¬ tions of the condenser. We may cause the molecules of the gas to collide by the use of alternate electric impulses of high frequency, and so we may imitate the process in a flame ; and from experiments with frequencies which we are now able to obtain, I think tha ; the result is producible wflth impulses which are transmissible through a con¬ ductor.

In connection with thoughts of a similar nature, it ap¬ peared to me of great interest to demonstrate the rigidity of a vibrating gaseous column. Although with such low frequencies as, say 10,000 per second, which I was able to obtain without difficulty from a specially constructed alternator, the task looked discouraging at first, I made a series of experiments. The trials with air at ordinary press¬ ure led to no result, but with air moderately rarefied I obtain what I think to be an unmistakable experimental evidence of the property sought for. As a result of this kind might lead able investigators to conclusions of im¬ portance I will describe one of the experiments performed.

It is well known that when a tube is slightly exhausted the discharge may be passed through it in the form of a thin luminous thread. When produced with currents of low frequency, obtained from a coil operated as usual, this thread is inert. If a magnet be approached to it, the part near the same is attracted or repelled, according to the di¬ rection of the lines of force of the magnet. It occurred to

11?

me that if such a thread would be produced with currents of very high frequency, it should be more or less rigid, and as it was visible it could be easily studied. Accordingly I prepared a tube about 1 inch in diameter and 1 metre long, with outside coating at each end. The tube was exhausted to a point at which by a little working the. thread discharge could be obtained. It must be remarked here that the general aspect of the tube, and the degree of exhaus¬ tion, are quite different than wThen ordinary low fre¬ quency currents are used. As it was found prefer¬ able to work with one terminal, the tube prepared was suspended from the end of a wire connected to the terminal, the tinfoil coating being connected to the wire, and to the lower coating sometimes a small insulated plate was attached. When the thread was formed it ex¬ tended through the upper part of the tube and lost itself in the lower end. If it possessed rigid ty it resembled, not exactly an elastic cord stretched tight between two sup¬ ports, but a cord suspended from a height with a small weight attache! at the end. When the finger or a magnet was approached to the upper end of the luminous thread, it could be brought locally out of position by electrostatic or magnetic action ; and when the disturbing object was very quickly removed, an analogous result was produced, as though a suspended cord would be displaced and quickly released near the point of suspension. In doing this the luminous thread was set in vibration, and two very sharply marked nodes, and a third indistinct one, were formed. The vibration, once set up, continued for fully eight minutes, dying gradually out. The speed of the vibration

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often varied perceptibly, and it could be observed that the electrostatic attraction of the glass affected the vibrating thread ; but it was clear that the electro¬ static action was not the cause of the vibration, for the thread was most generally stationary, and could always be set in vibration by passing the finger quickly near the upper part of the tube. With a magnet the thread could be split in two and both parts vibrated. By approaching the hand to the lower coating of the tube, or insulated plate if attached, the vibration was quickened; also, as far as I could see, by raising the potential or fre¬ quency. Thus, either increasing the frequency or passing a stronger discharge of the same frequency corresponded to a tightening of the cord. I did not obtain any experimental evidence with condenser discharges. A luminous band ex¬ cited in a bulb by repeated discharges of a Leyden jar must possess rigidity, and if deformed and suddenly released should vibrate. But probably the amount of vibrating mat¬ ter is so small that in spite of the extreme speed the inertia cannot prominently assert itself. Besides, the observation in such a case is rendered extremely difficult on account of the fundamental vibration.

The demonstration of the fact— which still needs better experimental confirmation — that a vibrating gaseous col¬ umn possesses rigidity, might greatly modify the views of thinkers. When with low frequencies and insignificant potentials indications of that property may be noted, how must a gaseous medium behave under the influence of enor¬ mous electrostatic stresses which may be active in the inter¬ stellar space, and which may alternate with inconceivable

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rapidity? The existence of such an electrostatic, rhyth¬ mically throbbing force— of a vibrating electrostatic field— would show a possible way how solids might have formed from the ultra-gaseous uterus, and how transverse and all kinds of vibrations may be transmitted through a gaseous medium filling all space. Then, ether might be a true fluid, devoid of rigidity, and at rest, it being merely neces¬ sary as a connecting link (o enable interaction. What de¬ termines the rigidity of a body ? It must be the speed and the amount of moving matter. In a gas the speed may be considerable, but the density is exceedingly small ; in a liquid the speed would be likely to be small, though the density may be considerable ; and in both cases the inertia resistance offered to displacement is practically nil. But place a gaseous (or liquid) column in an intense, rapidly alternating electrostatic field, set the particles vibrating with enormous speeds, then the inertia resistance asserts it¬ self. A body might move with more or less freedom through the vibrating mass, but as a whole it would be rigid.

There is a subject which I must mention in connection with these experiments : it is that of high vacua. This is a subject the study of which is not only interesting, but use¬ ful, for it may lead to results of great practical importance. In commercial apparatus, such as incandescent lamps, operated from ordinary systems of distribution, a much higher vacuum than obtained at present would not secure a very great advantage. In such a case the work is performed on the filament and the gas is little concerned; the improve¬ ment, therefore, would be but trifling. But when we be¬ gin to use very high frequencies and potentials, the action

120

of the gas becomes all important, and the degree of exhaus¬ tion materially modifies the results. As long as ordinary coils, even very large ones, were used, the study of the subject was limited, because just at a point when it became most interesting it had to be interrupted on account of the “non-striking” vacuum being reached. But presently we are able to obtain from a small disruptive discharge coil potentials much higher than even the largest coil was capable of giving, and, what is more, we can make the potential alternate with great rapidity. Both of these results enable us now to pass a luminous discharge through almost any vacua obtainable, and the field of our investigations is greatly extended. Think we as we may, of all the possible directions to develop a practical illuminant, the line of high vacua seems to be the most promising at present. But to reach extreme vacua the appliances must be much more improved, and ultimate perfection will not be attained until we shall have discarded the mechanical and perfected an electrical vacuum pump. Molecules and atoms can be thrown out of a bulb under the action of an enormous potential : this will be the principle of the vacuum pump of the future. For the present, we must secure the best results we can with mechanical appliances. In this respect, it might not be out of the way to say a few words about the method of, and apparatus for, producing excessively high degrees of exhaustion of which I have availed myself in the course of these investigations. It is very probable that other experimenters have used similar arrange¬ ments ; but as it is possible that there may be an item of interest in their description, a few remarks, which

121

will render this investigation more complete, might be per¬ mitted.

The apparatus is illustrated in a drawing shown in Fig. 30. S represents a Sprengel pump, which has been

Fig. 30.— Apparatus Used for Obtaining High Degrees

of Exhaustion.

specially constructed to better suit the work required. The stop-cock which is usually employed has been omitted, and instead of it a hollow stopper s has been fitted in the neck

of the reservoir R. This stopper has a small hole h, through which the mercury descends; the size of the outlet o being properly determined with respect to the section of the fall tube t, 'which is sealed to the reservoir instead of being connected to it in the usual manner. This arrange¬ ment overcomes the imperfections and troubles which often arise from the use of the stopcock on the reservoir and the connection of die latter with the fall tube.

The pump is connected through a U-shaped tube t to a very large reservoir Rx. Especial care was taken in fitting the grinding surfaces of the stoppers p and px, and both of these and the mercury caps above them were made excep¬ tionally long. After the U-shaped tube was fitted and put in place, it was heated, so as to soften and take off the strain resulting from imperfect fitting. The U-shaped tube was provided with a stopcock C, and two ground connec¬ tions g and gx — one for a small bulb b, usually containing caustic potash, and the other for the receiver r, to be exhausted.

The reservoir Rx was connected by means of a rubber tube to a slightly larger reservoir R2, each of the two reservoirs being provided with a stopcock Cx and C2, re¬ spectively. The reservoir R2 could be raised and lowered by a wheel and rack, and the range of its motion was so determined that when it was filled with mercury and the stopcock C2 closed, so as to form a Torricellian vacuum in it when raised, it could be lifted so high that the mercury in reservoir Rx would stand a little above stopcock Cx ; and when this stopcock was closed and the reservoir R2 descended, so as to form a Torricellian vacuum in

123

reservoir R^ it could be lowered so far as to completely empty the latter, the mercury filling the reservoir Rs up to a little above stopcock C2.

The capacity of the pump and of the connections was taken as small as possible relatively to the volume of reser¬ voir, Rlt since, of course, the degree of exhaustion depend¬ ed upon the ratio of these quantities.

With this apparatus I combined the usual means indi¬ cated by former experiments for the production of very high vacua. In most of the experiments it was convenient to use caustic potash. I may venture to say, in regard to its use, that much time is saved and a more perfect action of the pump insured by fusing and boiling the potash as soon as, or even before, the pump settles down. If this course is not followed the sticks, as ordinarily employed, may give moisture off at a certain very slow rate, and the pump may work for many hours without reaching a very high vacuum. The potash was heated either by a spirit lamp or by passing a discharge through it, or by passing a current through a wire contained in it. The advantage in the latter case was that the heating could be more rapidly repeated.

Generally the process of exhaustion was the following: — At the start, the stop-cocks C and being open, and all other connections closed, the reservoir R» was raised so far that the mercury filled the reservoir Rt and a part of the narrow connecting U-shaped tube. When the pump was set to work, the mercury would, of course, quickly rise in the tube, and reservoir R2 was lowered, the experimenter keeping the mercury at about the same level. The reser-

124

voir R2 was balanced by a long spring which facilitated the operation, and the friction of the parts was generally suf¬ ficient to keep it almost in any position. When the Sprengel pump had done its work, the reservoir R2 was further lowered and the mercury descended in Rl and filled R2, whereupon stopcock C2 was closed. The air adhering to the walls of Rt and that absorbed by the mercury was car¬ ried off, and to free the mercury of all air the reservoir R2 was for a long time worked up and down. During this proc¬ ess some air, which would gather below stopcock C2, was expelled from R2 by lowering it far enough and open¬ ing the stopcock, closing the latter again before raising the reservoir. When all the air had been expelled from the mercury, and no air would gather in R2 when it was lowered, the caustic potash was resorted to. The reservoir R2 was now again raised until the mercury in Rl stood above stopcock C^. The caustic potash was fused and boiled, and the moisture partly carried off by the pump and partly re-absorbed; and this process of heating and cooling was repeated many times, and each time, upon the moisture being absoibed or carried off, the reservoir R2 was for a long time raised and lowered. In this man¬ ner all the moisture was carried off from the mercury, and both the reservoirs were in proper condition to be used. The reservoir R2 was then again raised to the top, and the pump was kept working for a long time. When the high¬ est vacuum obtainable with the pump had been reached the potash bulb was usually wrapped with cotton which was sprinkled with ether so as to keep the potash at a very low temperature, then the reservoir R2 was lowered, and

125

upon reservoir Rl being emptied the receiver r was quickly sealed up.

When a new bulb was put on, the mercury was always raised above stopcock Cl5 which was closed, so as to always keep the mercury and both the reservoirs in fine condition, and the mercury was never withdrawn from Rl except when the pump had reached the highest degree of exhaustion. It is necessary to observe this rule if it is desired to use the apparatus to advantage.

By means of this arrangement I was able to proceed very quickly, and when the apparatus was in perfect order it was possible to reach the phosphorescent stage in a small bulb in less than 15 minutes, which is certainly very quick work for a small laboratory arrangement requiring all in all about 100 pounds of mercury. With ordinary small bulbs the ratio of the capacity of the pump, receiver, and connections, and that of reservoir R was about 1-20, and the degrees of exhaus¬ tion reached were necessarily very high, though I am unable to make a precise and reliable statement how far the ex¬ haustion was carried.

What impresses the investigator most in the course of these experiences is the behavior of gases when subjected to great rapidly alternating electrostatic stresses. But he must remain in doubt as to whether the effects observed are due wholly to the molecules, or atoms, of the gas which chemical analysis discloses to us, or whether there enters into play another medium of a gaseous nature, comprising atoms, or molecules, immersed in a fluid pervading the space. Such a medium surely must exist, and I am con¬ vinced that , for instance, even if air were absent, the sur-

126

face and neighborhood of a body in space would be heated by rapidly alternating the potential of the body; but no such heating of the surface or neighborhood could occur if all free atoms were removed and only a homogeneous, in¬ compressible, and elastic fluid — such as ether is supposed to be — would remain, for then there would be no impacts, no collisions. In such a case, as far as the body itself is con¬ cerned, only frictional losses in the inside could occur.

It is a striking fact that the discharge through a gas is established with ever increasing freedom as the frequency of the impulses is augmented. It behaves in this respect quite contrarily to a metallic conductor. In the latter the impedance enters prominently into play as the frequency is increased, but the gas acts much as a series of conden¬ sers would: the facility with which the discharge passes through seems to depend on the rate of change of potential. If it act so, then in a vacuum tube even of great length, and no matter how strong the current, self-induction could not assert itself to any appreciable degree. We have, then, as far as we can now see, in the gas a conductor which is capa¬ ble of transmitting electric impulses of any frequency which we may be able to produce. Could the frequency be brought high enough, then a queer system of electric distribution, which would be likely to interest gas companies, might be re¬ alized : metal pipes filled with gas — the metal being the in¬ sulator, the gas the conductor — supplying phosphorescent bulbs, or perhaps devices as yet uninvented. It is certainly possible to take a hollow core of copper, rarefy the gas' in the same, and by passing impulses of sufficiently high fre¬ quency through a circuit around it, bring the gas inside to

127