Experiments with Alternate Currents of High Potential and High Frequency (1892) — part 4 of 8

tained in a glass stem sealed in the bulb ; care being taken, of course, to make everything as nearly alike as possible. On each glass stem in the inside of the bulb was slipped a highly polished tube made of aluminium sheet, which litted the stem and was held on it by spring pressure. The function of this aluminium tube will be explained subsequently. In each bulb an equal length of filament protruded above the metal tube. It is sufficient to say now that under these conditions equal lengths of filament of the same thick¬ ness — in other words, bodies of equal bulk — were brought to incandescence. The three bulbs were sealed to a glass tube, which was connected to a Sprengel pump. When a high vacuum had been reached, the glass tube carrying the bulbs was sealed off. A current was then turned on suc¬ cessively on each bulb, and it was found that the filaments came to about the same brightness, and, if anything, tho smallest bulb, which was placed midway between the two larger ones, may have been slightly brighter. This result was expected, for when either of the bulbs was connected to the coil the luminosity spread through the other two, hence the three bulbs constituted really one vessel. When all the three bulbs were connected in multiple arc to the coil, in the largest of them the filament glowed brightest, in the next smaller it was a little less bright, and in the smallest it only came to redness. The bulbs were then sealed off and separately tried. The brightness of the fil¬ aments was now such as would have been expected on the supposition that the energy given off was proportionate to the surface of the bulb, this surface in each case represent-

62

mg one of the coatings of a condenser. Accordingly, there was less difference between the largest and the middle sized than between the latter and the smallest bulb.

An interesting observation was made in this experiment. The three bulbs were suspended fiem a straight bare wire connected to a terminal of the coil, the largest bulb being placed at the end of the wire, at some distance from it the smallest bulb, and an equal distance from the latter the middle-sized one. The carbons glowed then in both the larger bulbs about as expected, but the smallest did not get its share by far. This observation led me to exchange the position of the bulbs, and I then observed that whichever of the bulbs was in the middle it was by far less bright than it was in any other position. This mystifying result was, of course, found to be due to the electrostatic action between the bulbs. When they were placed at a considerable dis¬ tance, or when they were attached to the corners of an equilateral triangle of copper wire, they glowed about in the order determined by their surfaces.

As to the shape of the vessel, it is also of some impor¬ tance, especially at high degrees of exhaustion. Of all the possible constructions, it seems that a spherical globe with the refractory body mounted in its centre is the best to em¬ ploy. In experience it has been demonstrated that in such a globe a refractory body of a given bulk is more easily brought to incandescence than when otherwise shaped bulbs are used. There is also an advantage in giving to the incandescent body the shape of a sphere, for self-evident reasons. In any case the body should be mounted in the centre, where the atoms rebounding from the glass collide.

63

This object is best attained in the spherical bulb ; but it is also attained in a cylindrical vessel with one or two straight filaments coinciding with its axis, and possibly also in par¬ abolical or spherical bulbs with the refractory body or bodies placed in the focus or foci of the same; though the latter is not probable, as the electrified atoms should in all cases rebound normally from the surface they strike, unless the speed were excessive, in which case they would prob¬ ably follow the general law of reflection. No mat er what shape the vessel may have, if the exhaustion be low, a fila¬ ment mounted in the globe is brought to the same degree of incandescence in all parts; but if the exhaustion be high and the bulb be spherical or pear-shaped, as usual, focal points form and the filament is heated to a higher degree at or near such points.

To illustrate the effect, I have here two small bulbs which are alike, only one is exhausted to a low and the other to a very high degree. When connected to the coil, the fila¬ ment in the former glows uniformly throughout all its length; whereas in the latter, that portion of the filament which is in the centre of the bulb glows far more intensely than the rest. A curious point is that the phenomenon occurs even if two filaments are mounted in a bulb, each being connected to one terminal of the coil, and, what is still more curious, if they be very near together, provided the vacuum be very higji. I noted in experiments with such bulbs that the filaments would give way usually at a certain point, and in the first trials I attributed it to a defect

in the carbon. But when the phenomenon occurred many %

times in succession I recognized its real cause.

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In order to bring a refractory body inclosed in a bulb to incandescence, it is desirable, on account of economy, that all the energy supplied to the bulb from the source should reach without loss the body to be heated; from there, and from nowhere else, it should be radiated. It is, of course, out of the question to reach this theoretical re¬ sult, but it is possible by a proper construe! ion of the illu¬ minating device to approximate it more or less.

For many reasons, the refractory body is placed in che centre of the bulb, and it is usually supported on a glass stem containing the leading-in wire. As the potential of this wire is alternated, the rarefied gas surrounding the stem is acted upon inductively, and the glass stem is vio¬ lently bombarded and heated. In this manner by far the greater portion of the energy supplied to the bulb — es¬ pecially when exceedingly high frequencies are used — may be lost for the purpose contemplated. To obviate this loss, or at least to reduce it to a minimum, I usually screen the rarefied gas surrounding the stem from the inductive action of the leading-in wire by providing the stem with a tube or coating of conducting material. It seems beyond doubt that the best among metals to employ for this purpose is aluminium, on account of its many remarkable properties. Its only fault is that it is easily fusible, and, therefore, its distance from the incandescing body should be properly estimated. Usually, a thin tube, of a diameter somewhat smaller than that c f the glass stem, is made of the finest aluminium sheet, and slipped on the stem. The tube is conveniently prepared by wrapping around a rod fastened in a lathe a piece of alu-

minium sheet of the proper size, grasping the sheet firmly with clean chamois leather or blotting paper, and spinning the rod very fast. The sheet is wound tightly around the rod, and a highly polished tube of one or three layers of the sheet is obtainnd. When slipped on the stem, the pressure is generally sufficient to prevent it from slipping off, but, for safety, the lower edge of the sheet may be turned in¬ side. The upper inside corner of the sheet — that is, the one which is nearest to the refractory incandescent body — should be cut out diagonally, as it often happens that, in consequence of the intense heat, this corner turns toward the inside and comes very near to, or in contact with, the wire, or filament, supporting the refractory body. The greater part of the energy supplied to the bulb is then used up in heating the metal tube, anel the bulb is rendered useless for the purpose. The aluminium sheet should project above the glass stem more or less — one inch or so — or else, if the glass be too close to the incandes¬ cing body, it may be strongly heated and become more or less conducting, whereupon it may be ruptured, or may, by its conductivity, establish a good electrical connection be¬ tween the metal tube and the leading-in wire, in which case, again, most of the energy will be lost in heating the former. Perhaps the best way is to make the top of the glass tube, for about an inch, of a much smaller diameter. To still further reduce the danger arising from the heating of the glass stem, and also with the view of preventing an electric¬ al connection between the metal tube and the electrode, I preferably wrap the stem with several layers of thin mica, which extends at least as far as the metal tube. In

66

some bulbs I have also used an outside insulating cover.

The preceding remarks are only made to aid the experi¬ menter in the first trials, for the difficulties which he en¬ counters he may soon find means to overcome in his own way.

To illustrate the effect of the screen, and the advantage of using it, I have here two bulbs of the same size, with their stems, leading-in wires and incandescent lamp fila¬ ments tied to the latter, as uearly alike as possible. The stem of one bulb is provided with an aluminium tube, the stem of the other has none. Originally the two bulbs were joined by a tube which was connected to aSprengel pump. When a high vacuum had been reached, first the connect¬ ing tube, and then the bulbs, were sealed off ; they are therefore of the same degree of exhaustion. When they

are separately connected to the coil giving a certain poten-

«

tial, the carbon filament in the bulb provided with the aluminium screen is rendered highly incandescent, while the filament in the other bulb may, with the same po¬ tential, not even come to redness, although in reality the latter bulb takes generally more energy than the former. When they are both connected together to the terminal, the difference is even more ap¬ parent, showing the importance of the screening. The metal tube placed on the stem containing the leading-in wire performs really two distinct functions: First; it acts more or less as an electrostatic screen, thus economizing the energy supplied to the bulb; and, second, to whatever extent it may fail to act electrostatically, it acts mechanic-

ally, preventing the bombardment, and consequently in¬ tense heating and possible deterioration of the slender sup¬ port of the refractory incandescent body, or of the glass stem containing the leading-in wire. I say slender sup¬ port, for it is evident that in order to confine the heat more completely to the incandescing body its support should be very thin, so as to carry away the smallest possible amount of heat by conduction. Of all the supports used I have found an ordinary incandescent lamp filament to be the best, principally because among conductors it can with¬ stand the highest degrees of heat.

The effectiveness of the metal tube as an electrostatic screen depends largely on the degree of exhaustion.

At excessively high degrees of exhaustion — which are reached by using great care and special means in connection with the Sprengel pump — when the matter in the globe is in the ultra-radiant state, it acts most perfectly. The shadow of the upper edge of the tube is then sharply defined upon the bulb.

At a somewhat lower degree of exhaustion, which is about the ordinary “non-striking” vacuum, and generally as long as the matter moves predominantly in straight lines, the screen still does well. In elucidation of the preceding re¬ mark it is necessary to state that what is a “non-striking” vacuum for a coil operated, as ordinarily, by impulses, or currents, of lowfrequency, is not, by far, so when the coil is operated by currents of very high frequency. In such case the discharge may pass with great freedom through the rarefied gas through which a low-frequency discharge may not pass, even though the potential be much higher. At

ordinary atmospheric pressures just the reverse rule Jkolds good: the higher the frequency, the less the spark discharge is able to jump between the terminals, especially if they are knobs or spheres of some size. I

Finally, at very low degrees of exhaustion, when the gas is well conducting, the metal tube not only does not act as an electrostatic screen, but even is a drawback, aiding to a considerable extent the dissipation of the energy laterally from the leading-in wire. This, of course, is to be expected. In this case, namely, the metal tube is in good electrical connection wdth the leading-in wire, and most of the bom¬ bardment is directed upon the tube. As long as the elec¬ trical connection is not good, the conducting tube is always

of some advantage, for although it may not greatly econo-

• ^ v*

mize energy, still it protects the support of the refractory button, and is a means for concentrating more energy upon the same.

To whatever extent the aluminium tube performs the func¬ tion of a screen, its usefulness is therefore limited to very high degrees of exhaustion when it is insulated from the elec¬ trode — that is, when the gas as a whole is non-conducting, and the molecules, or atoms, act as independent carriers of electric charges.

In addition to acting as a more or less effective screen, in the true meaning of the word, the conducting tube or coat¬ ing may also act, by reason of its conductivity, as a sort of equalizer or dampener of the bombardment against the stem. To be explicit, I assume the action as follows : Sup¬ pose a rhythmical bombardment to occur against the con¬ ducting tube by reason of its imperfect action as a screen.

60

it certainly must happen that some molecules, or atoms, strike the tube sooner than others. Those which come first in contact with it give up their superfluous charge, and the tube is electrified, the electrification in¬ stantly spreading over its surface. But this must diminish the energy lost in the bombardment for two reasons: first, the charge given up by the atoms spreads over a great area, and hence the electric density at any point is small, and the atoms are repelled with less energy than they would be i f they would strike against a good in¬ sulator; secondly, as the tube is electrified by the atoms which first come in contact with it, the progress of the fol¬ lowing atoms against the tube is more or less checked by the repulsion which the electrified tube must exert upon the similarly electrified atoms. This repulsion may per¬ haps be sufficient to prevent a large portion of the atoms from striking the tube, bat at any rate it must diminish the energy of their impact. It is clear that when the exhaus¬ tion is very low, and the rarefied gas well conducting, neither of the above effects can occur, and, on the other hand, the fewer the atoms, with the greater freedom they move; in other words, the higher the degree of exhaustion, up to a limit, the more telling will be both the effects.

What I have just said may afford an explanation of the phenomenon observed by Prof. Crookes, namely, that a discharge through a bulb is established with much greater facility when an insulator than when a conductor is pres¬ ent in the same. In my opinion, the conductor acts as a dampener of the motion of the atoms in the two ways pointed out; hence, to cause a visible discharge to pass

70

through the bulb, a much higher potential is needed if a conductor, especially of much surface, be present.

For the sake of clearness of some of the remarks before made, I must now refer to Figs. 18, 19 and 20, which illus¬ trate various arrangements with a type of bulb most gen¬ erally used.

Fig. 18.— Bulb with Mica Fig. 19.— Improved Bulb Tube and Aluminium with Socket and Screen. Screen.

Fig. 18 is a section through a spherical bulb L, with the glass stem s, containing the leading-in wire w, which has a lamp filament l fastened to it, serving to support the refractory button m in the centre. M is a sheet of thin

71

mica wound in several layers around the stem s, and a is the aluminium tube.

Fig. 19 illustrates such a bulb in a somewhat more ad¬ vanced stage of perfection. A metallic tube S is fastened by means of some cement to the neck of the tube. In the tube is screwed a plug P, of insulating material, in the centre of which is fastened a metallic terminal t, for the connection to the leading-in wire w. This terminal must be well insulated from the metal tube S , therefore, if the cement used is conducting — and most generally it is suf¬ ficiently so — the space between the plug P and the neck of the bulb should be filled with some good insulating material, as mica powder.

Fig. 20 shows a bulb made

for experimental purposes. In

this bulb the aluminium tube ^IG* 20.— Bule for Experi¬ ments with Conducting is provided with an external Tube.

connection, which serves to investigate the effect of the

tube under various conditions. It is referred to chiefly to

suggest a line of experiment followed.

Since the bombardment against the stem containing the leading-in wire is due to the inductive action of the latter upon the rarefied gas, it is of advantage to reduce this ac-

72

tion as far as practicable by employing a very thin wire,

• surrounded by a very thick insulation of glass or other ma¬ terial, and by making the wire passing through the rarefied gas as short as practicable. To combine these features I employ a large tube T (Fig. 21), which protrudes into the bulb to some distance, and carries on the top a very short glass stem s, into which is sealed the leading-in wire w, and I protect the top of the glass stem against the heat by a small, aluminium tube a and a layer of mica underneath the same, as usual. The wire w , passing through the large tube to the outside of the bulb, should be well insulated — with a glass tube, for instance — and the space between ought to be filled out with some excellent insulator. Among many insulating powders I have tried, I have found that mica powder is the best to employ. If this precaution is not taken, the tube T, protruding into the bulb, will surely be cracked in consequence of the heating by the brushes which are apt to form in the upper part of the tube, near the exhausted globe, especially if the vacuum be excellent, and therefore the potential necessary to operate the lamp very high.

Fig. 22 illustrates a similar arrangement, with a large tube T protruding into the part of the bulb containing the refractory button m. In this case the wire leading from the outside into the bulb is omitted, the energy required being supplied through condenser coatings C C. The insulat¬ ing packing P should in this construction be tightly fitting to the glass, and rather wide, or otherwise the discharge might avoid passing through the wire w, which connects the inside condenser coating to the incandescent button in.

73

The molecular bombardment against the glass stem in

the bulb is a source of great trouble. As illustration I will cite a phenomenon only too frequently and unwillingly observed. A bulb, preferably a large one, may be taken,

O

Fig. 21.— Improved Bulb with Non-Conducting Button.

without Leading-In Wire.

and a good conducting body, such as a piece of carbon, may be mounted in it upon a platinum wire sealed in the glass stem. The bulb may be exhausted to a fairly high degree, nearly to the point when phosphorescence begins to appear.

When the bulb is connected with the coil, the piece of carbon, if small, may become highly incandescent at first, but its brightness immediately diminishes, and then the discharge may break through the glass somewhere in the middle of the stem, in the form of bright sparks, in spite of the fact that the platinum wire is in good electrical con¬ nection with the rarefied gas through the piece of carbon or metal at the top. The first sparks are singularly bright, recalling those drawn from a clear surface of mercury. But, as they heat the glass rapidly, they, of course, lose their brightness, and cease when the glass at the ruptured place becomes incandescent, or generally sufficiently • hot to con¬ duct. | When observed for the first time the phenomenon must appear very curious, and shows in a striking manner how radically different alternate currents, or impulses, of high frequency behave, as compared with steady currents, or currents of low frequency^ With such currents — namely, the latter — the phenomenon would of course not occur. When frequencies such as are obtained by mechanical means are used, I think that the rupture of the glass is more or less the consequence of the bombardment, which warms it up and impairs its insulating power; but with frequencies obtainable with condensers I have no doubt that the glass may give way without previous heating. Al¬ though this appears most singular at first, it is in reality what we might expect to occur. The energy supplied to the wire leading into the bulb is given off partly by direct action through the carbon button, and partly by inductive action through the glass surrounding the wire. The case is thus analogous to that in which a condenser shunted by a

75

conductor of low resistance is connected to a source of al¬ ternating currents. As long as the frequencies are low, the conductor gets the most, and the condenser is perfectly safe; but when the frequency becomes excessive, the role of the conductor may become quite insignificant. In the

Fig. 23.— Effect Produced by a Ruby Drop.

latter case the difference of potential at the terminals of the condenser may become so great as to rupture the di¬ electric, notwithstanding the fact that the terminals are joined by a conductor of low resistance,

76

It is, of course, not necessary, when it is desired to pro¬ duce the incandescence of a body inclosed in a bulb by means of these currents, that the body should be a con¬ ductor, for even a perfect non-conductor may be quite as readily heated. For this purpose it is sufficient to sur¬ round a conducting electrode with a non-conducting ma¬ terial, as, for instance, in the bulb described before in Fig. 21, in which a thin incandescent lamp filament is coated with a non-conductor, and supports a button of the same material on the top. At the start the bombardment goes on by inductive action through the non-conductor, until the same is sufficiently heated to become conducting, when the bombardment continues in the ordinary way.

A different arrangement used in some of the bulbs con¬ structed is illustrated in Fig. 23. In this instance a non-con¬ ductor m is mounted in a piece of common arc light carbon so as to project some small distance above the latter. The car¬ bon piece is connected to the leading-in wire passing through a glass stem, which is wrapped with several layers of mica. An aluminium tube a is employed as usual for screening. It is so arranged that it reaches very nearly as high as the carbon and only the non-conductor m projects a little above it. The bombardment goes at first against the upper surface of carbon, the lower parts being protect¬ ed by the aluminium tube. As soon, however, as the non¬ conductor m is heated it is rendered good conducting, and then it becomes the centre of the bombardment, being most exposed to the same.

I have also constructed during these experiments many such single-wire bulbs with or without internal electrode,

77

in which the radiant matter was projected against, or fo¬ cused upon, the body to be rendered incandescent. Fig. 24 illustrates one of the bulbs used. It consists of a spherical globe L, provided with a long neck n, on the top, for in¬ creasing the action in some cases by the application of an external conducting coating. The globe L is blown out on the bottom into a very small bulb 5* which serves to hold it firmly in a socket S of insulating material into which it is cemented. A fine lamp filament /, supported on a wire w, passes through the centre of the globe L. The filament is rendered incandescent in the middle portion, where the bombardment proceeding from the lower inside surface of the globe is most intense. The lower portion of the globe, as far as the socket S reaches, is rendered con¬ ducting, either by a tinfoil coating or otherwise, and the external electrode is connected to a terminal of the coil.

The arrangement diagram matically indicated in Fig. 24 was found to be an inferior one when it was desired to ren¬ der incandescent a filament or button supported in the centre of the globe, but it was convenient when the object was to excite phosphorescence.

In many experiments in which bodies of a different kind were mounted in the bulb as, for instance, indicated in Fig. 23, some observations of interest were made.

It was found, among other things, that in such cases, no matter where the bombardment began, just as soon as a high temperature was reached there was generally one of the bodies which seemed to take most of the bombardment upon itself, the other, or others, being thereby relieved. This quality appeared to depend principally on the point of

78

fusion, and on the facility with which the body was “evaporated,” or, generally speaking, disintegrated — mean- ing by the latter term not only the throwing off of atoms, but likewise of larger lumps. The observation made was in accordance with generally accepted notions. In a highly exhausted bulb electricity is carried off from the electrode by independent carriers, which are partly the atoms, or molecules, of the residual atmosphere, and partly the atoms, molecules, or lumps thrown off from the electrode. If the electrode is composed of bodies of different character, and if one of these is more easily disintegrated than the others, most of the electricity supplied is carried off from that body, which is then brought to a higher temperature than the others, and this the more, as upon an increase of the tem¬ perature the body is still more easily disintegrated.

It seems to me quite probable that a similar process takes place in the bulb even with a homogeneous electrode, and I think it to be the principal cause of the disintegration. There is bound to be some irregularity, even if the surface is highly polished, which, of course, is impossible with most of the refractory bodies employed as electrodes. Assume that a point of the electrode gets hotter, instantly most of the discharge passes through that point, and a minute patch is probably fused and evaporated. It is now possible that in consequence of the violent disintegration the spot attacked sinks in temperature, or that a counter force is created, as in an arc; at any rate, the local tearing off meets with the limitations incident to the experiment, where¬ upon the same process occurs on another place. To the eye the electrode appears uniformly brilliant.

79

79

but there are upon it points constantly shiftin wandering around, of a temperature far above mean, and this materially hastens the process of deteriora¬ tion. That some such thing occurs, at least when the elec¬ trode is at a lower temperature, sufficient experimental evi¬ dence can be obtained in the following manner : Exhaust a bulb to a very high degree, so that with a fairly high poten¬ tial the discharge cannot pass — that is, not a luminous one, for a weak invisible discharge occurs always, in all prob¬ ability. Now raise slowly and carefully the potential, leav¬ ing the primary current on no more than for an instant. At a certain point, two, three, or half a dozen phosphorescent spots will appear on the globe. These places of the glass are evidently more violently bombarded than others, this being due to the unevenly distributed electric density, necessitated, of course, by sharp projections, or, generally speaking, ir¬ regularities of the electrode. But the luminous patches are constantly changing in position, which is especially well ob¬ servable if one manages to produce very few, and this in¬ dicates that the configuration of the electrode is rapidly changing.

From experiences of this kind I am led to infer that, in order to be most durable, the refractory button in the bulb should be in the form of a sphere with a highly polished surface. Such a small sphere could be manu¬ factured from a diamond or some other crystal, but a bet¬ ter way would be to fuse, by the employment of extreme degrees of temperature, some oxide — as, for instance, zir- conia — into a small drop, and then keep it in the bulb at a temperature somewhat below its point of fusion.

80

Interesting and useful results can no doubt be reached in the direction of extreme degrees of heat. How can such high temperatures be arrived at ? How are the highest degrees of heat reached in nature ? By the impact of stars, by high speeds and collisions. In a collision any rate of heat generation may be attained. In a chemical process we are limited. When oxygen and hydrogen com¬ bine, they fall, metaphorically speaking, from a definite height. We cannot go very far with a blast, nor by con¬ fining heat in a furnace, but in an exhausted bulb we can concentrate any amount of energy upon a minute button. Leaving practicability out of consideration, this, then, would be the means which, in my opinion, would enable us to reach the highest temperature. But a great difficulty when proceeding in this way is encountered, namely, in most cases the body is carried off before it can fuse and form a drop. This difficulty exists principally with an ox¬ ide such as zirconia, because it cannot be compressed in so hard a cake that it would not be carried off quickly. . I en¬ deavored repeatedly to fuse zirconia, placing it in a cup or arc light carbon as indicated in Fig. 23. It glowed with a most intense light, and the stream of the particles project¬ ed out of the carbon cup was of a vivid white; but whether it was compressed in a cake or made into a paste with • carbon, it was carried off before it could be fused. The carbon cup containing the zirconia had to be mounted very low in the neck of a large bulb, as the heating of the glass by the projected particles of the oxide was so rapid that in the first trial the bulb was cracked almost in an instant when the current was turned on. The heating of the glass

81

by the projected particles was found to be always greater when the carbon cup contained a body which was rapidly carried off — I presume because in such cases, with the same potential, higher speeds were reached, and also because, per unit of time, more matter was projected — that is, more particles would strike the glass.

The before mentioned difficulty did not exist, however, when the body mounted in the carbon cup offered great re¬ sistance to deterioration. For instance, when an oxide was first fused in an oxygen blast and then mounted in the bulb, it melted very readily into a drop.

Generally during the process of fusion magnificent light effects were noted, of which it would be difficult to give an adequate idea. Fig. 28 is intended to illustrate the effect observed with a ruby drop. At first one may see a narrow funnel of white light projected against the top of the globe, where it produces an irregularly outlined phosphorescent patch. When the point of the ruby fuses the phosphores¬ cence becomes very powerful ; but as the atoms are pro¬ jected with much greater speed from the surface of the drop, soon the glass gets hot and “tired,” and now only the outer edge of the patch glows. In this manner an intensely phosphorescent, sharply defined line, l, corresponding to the outline of the drop, is produced, which spreads slowly over the globe as the drop gets larger. When the mass be¬ gins to boil, small bubbles and cavities are formed, which cause dark colored spots to sweep across the globe. The bulb may be turned downward without fear of the drop falling off, as the mass possesses considerable viscosity.

I may mention here another feature of some interest,

82

which I believe to have noted in the course of these ex¬ periments, though the observations do not amount to a certitude. It appeared that under the molecular impact caused by the rapidly alternating potential the body was fused and maintained in that state at a lower temperature in a highly exhausted bulb than was the case at normal pressure and application of heat in the ordinary way — that is, at least, judging from the quantity of the light emitted. One of the experiments performed may be men¬ tioned here by way of illustration. A small piece of pumice stone was stuck on a platinum wire, and first melted to it in a gas burner. The wire was next placed between two pieces of charcoal and a burner applied so as to produce an intense heat, sufficient to melt down the pumice stone into a small glass-like button. The platinum wire had to be taken of sufficient thickness to prevent its melting in the fire. While in the charcoal fire, or when held in a burner to get a better idea of the degree of heat, the button glowed with great brilliancy. The wire with the button was then mounted in a bulb, and upon exhaust¬ ing the same to a high degree, the current was turned on slowly so as to prevent the cracking of the button. The button was heated to the point of fusion, and when it melted it did not, apparently, glow with the same brilliancy as before, and this would indicate a lower temperature. Leaving out of consideration the observer’s possible, and even probable, error, the question is, can a body under these conditions be brought from a solid to a, liquid state with evolution of less light ?

When the potential of a body is rapidly alternated it is

88