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Tuesday, February 27, 2007


A different arrangement used in some of the bulbs constructed 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 carbon 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 protected 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, in
which the radiant matter was projected against, or focused 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 b, 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 conducting,
either by a tinfoil coating or otherwise, and the external electrode is connected to a terminal of the coil.
The arrangement diagrammatically 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 fusion, and on the facility with which the body was ·' evaporated," or, generally speaking,
disintegrated--meaning 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 temperature 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, whereupon the same process occurs on another place. To the eye the
electrode appears uniformly brilliant, but there axe upon it points constantly shifting and wandering around, of a
temperature far above the mean, and this materially hastens the process of deterioration. That some such thing
occurs, at least when the electrode is at a lower temperature, sufficient experimental evidence can be obtained in
the following manner : Exhaust a bulb to a very high degree, so that with a fairly high potential the discharge
cannot pass--that is, not a luminous one, for a weak invisible discharge occurs always, in all probability. Now raise
slowly and carefully the potential, leaving 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, irregularities of the electrode. But the luminous patches are
constantly changing in position, which is especially well observable if one manages to produce very few, and this
indicates 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 manufactured from a
diamond or some other crystal, but a better way would be to fuse, by the employment of extreme degrees of

temperature, some oxide--as, for instance, zirconia--into a small drop, and then keep it in the bulb at a
temperature somewhat below its point of fusion.
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 combine, they fall, metaphorically speaking, from a definite height. We
cannot go very far with a blast, nor by confining 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 oxide such as zirconia, because it cannot be compressed in so hard a cake that it
would not be carried off quickly. I endeavored 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 projected 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 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. 23 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 phosphorescence becomes very powerful; but as the
atoms are projected 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, I,
corresponding to the outline of the drop, is produced, which spreads slowly over the globe as the drop gets larger.
When the mass begins 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, which I believe to have noted in the
course of these experiments, 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 mentioned 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 exhausting 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 certain that the structure is jarred. When the potential is very high, although the vibrations
may be few--say 20,000 per second--the effect upon the structure may be considerable. Suppose, for example,
that a ruby is melted into a drop by a steady application of energy. When it forms a drop it will emit visible and
invisible waves, which will be in a definite ratio, and to the eye the drop will appear to be of a certain brilliancy.
Next, suppose we diminish to any degree we choose the energy steadily supplied, and, instead, supply energy
which rises and falls according to a certain law. Now, when the drop is formed, there will be emitted from it three
different kinds of vibrations--the ordinary visible, and two kinds of invisible waves : that is, the ordinary dark
waves of all lengths, and, in addition, waves of a well defined character. The latter would not exist by a steady
supply of the energy; still they help to jar and loosen the structure. If this really be the case, then the ruby drop will

emit relatively less visible and more invisible waves than before. Thus it would seem that when a platinum wire,
for instance, is fused by currents alternating with extreme rapidity, it emits at the point of fusion less light and more
invisible radiation than it does when melted by a steady current, though the total energy used up in the process of
fusion is the same in both cases. Or, to cite another example, a lamp filament is not capable of withstanding as long
with currents of extreme frequency as it does with steady currents, assuming that it be worked at the same luminous
intensity. This means that for rapidly alternating currents the filament should be shorter and thicker. The higher the
frequency--that is, the greater the departure from the steady flow--the worse it would be for the filament. But if
the truth of this remark were demonstrated, it would be erroneous to conclude that such a refractory button as used
in these bulbs would be deteriorated quicker by currents of extremely high frequency than by steady or low
frequency currents. From experience I may say that just the opposite holds good: the button withstands the
bombardment better with currents of very high frequency. But this is due to the fact that a high frequency discharge
passes through a rarefied gas with much greater freedom than a steady or low frequency discharge, and this will say
that with the former we can work with a lower potential or with a less violent impact. As long, then, as the gas is of
no consequence, a steady or low frequency current is better; but as soon as the action of the gas is desired and im-
portant, high frequencies are preferable.
In the course of these experiments a great many trials were made with all kinds of carbon buttons. Electrodes made
of ordinary carbon buttons were decidedly more durable when the buttons were obtained by the application of
enormous pressure. Electrodes prepared by depositing carbon in well known ways did not show up well; they
blackened the globe very quickly. From many experiences I conclude that lamp filaments obtained in this manner
can be advantageously used only with low potentials and low frequency currents. Some kinds of carbon withstand
so well that, in order to bring them to the point of fusion, it is necessary to employ very small buttons. In this case
the observation is rendered very difficult on account of the intense heat produced. Nevertheless there can be no
doubt that all kinds of carbon are fused under the molecular bombardment, but the liquid state must be one of great
instability. Of all the bodies tried there were two which withstood best--diamond and carborundum. These two
showed up about equally, but the latter was preferable, for many reasons. As it is more than likely that this body is
not yet generally known, I will venture to call your attention to it.
It has been recently produced by Mr. E. G. Acheson, of Monongahela City, Pa., U. S. A. It is intended to replace
ordinary diamond powder for polishing precious stones, etc., and I have been informed that it accomplishes this
object quite successfully. I do not know why the name "carborundum" has been given to it, unless there is
something in the process of its manufacture which justifies this selection. Through the kindness of the inventor, I
obtained a short while ago some samples which I desired to test in regard to their qualities of phosphorescence and
capability of withstanding high degrees of heat.
Carborundum can be obtained in two forms--in the form of "crystals" and of powder. The former appear to the
naked eye dark colored, but are very brilliant; the latter is of nearly the same color as ordinary diamond powder, but
very much finer. When viewed under a microscope the samples of crystals given to me did not appear to have any
definite form, but rather resembled pieces of broken up egg coal of fine quality. The majority were opaque, but
there were some which were transparent and colored. The crystals are a kind of carbon containing some impurities,
they are extremely hard, and withstand for a long time even an oxygen blast. When the blast is directed against
them they at first form a cake of some compactness, probably in consequence of the fusion of impurities they
contain. The mass withstands for a very long time the blast without further fusion ; but a slow Carrying off, or
burning, occurs, and, finally, a small quantity of a glass-like residue is left, which, I suppose, is melted alumina.
When compressed strongly they conduct very well, but not as well as ordinary carbon. The powder, which is
obtained from the crystals in some way, is practically non-conducting. It affords a magnificent polishing material
for stones.
The time has been too short to make a satisfactory study of the properties of this product, but enough experience
has been gained in a few weeks I have experimented upon it to say that it does possess some remarkable properties
in many respects. It withstands excessively high degrees of heat, it is little deteriorated by molecular bombardment,
and it does not blacken the globe as ordinary carbon does. The only difficulty which I have found in its use in
connection with these experiments was to find some binding material which would resist the heat and the effect of
the bombardment as successfully as carborundum itself does.
I have here a number of bulbs which I have provided with buttons of carborundum. To make such a button of
carborundum crystals I proceed in the following manner: I take an ordinary lamp filament and dip its point in tar, or
some other thick substance or paint which maybe readily carbonized. I next pass the point of the filament through
the crystals, and then hold it vertically over a hot plate. The tar softens and forms a drop on the point of the
filament, the crystals adhering to the surface of the drop. By regulating the distance from the plate the tar is slowly

dried out and the button becomes solid. I then once more dip the button in tar and hold it again over a plate until the
tar is evaporated, leaving only a hard mass which firmly binds the crystals. When a larger button is required I
repeat the process several times, and I generally also cover the filament a certain distance below the button with
crystals. The button being mounted in a bulb, when a good vacuum has been reached, first a weak and then a strong
discharge is passed through the bulb to carbonize the tar and expel all gases, and later it is brought to a very intense
When the powder is used I have found it best to proceed as follows: I make a thick paint of carborundum and tar,
and pass a lamp filament through the paint. Taking then most of the paint off by rubbing the filament against a
piece of chamois leather, I hold it over a hot plate until the tar evaporates and the coating becomes firm. I repeat
this process as many times as it is necessary to obtain a certain thickness of coating. On the point of the coated
filament I form a button in the same manner.
There is no doubt that such a button--properly prepared under great pressure--of carborundum, especially of
powder of the best quality, will withstand the effect of the bombardment fully as well as anything we know. The
difficulty is that the binding material gives way, and the carborundum is slowly thrown off after some time. As it
does not seem to blacken the globe in the least, it might be found useful for coating the filaments of ordinary incan-
descent lamps, and I think that it is even possible to produce thin threads or sticks of carborundum which will re-
place the ordinary filaments in an incandescent lamp. A carborundum coating seems to be more durable than other
coatings, not only because the carborundum can withstand high degrees of heat, but also because it seems to unite
with the carbon better than any other material I have tried. A coating of zirconia or any other oxide, for instance, is
far more quickly destroyed. I prepared buttons of diamond dust in the same manner as of carborundum, and these
came in durability nearest to those prepared of carborundum, but the binding paste- gave way much more quickly
in the diamond buttons : this, however, I attributed to the size and irregularity of the grains of the diamond.
It was of interest to find whether carborundum possesses the quality of phosphorescence. One is, of course,
prepared to encounter two difficulties: first, as regards the rough product, the "crystals," they are good conducting,
and it is a fact that conductors do not phosphoresce ; second, the powder, being exceedingly fine, would not be apt
to exhibit very prominently this quality, since we know that when crystals, even such as diamond or ruby, are finely
powdered, they lose the property of phosphorescence to a considerable degree.
The question presents itself here, can a conductor phosphoresce? What is there in such a body as a metal, for in-
stance, that would deprive it of the quality of phosphorescence, unless it is that property which characterizes it as a
conductor? for it is a fact that most of the phosphorescent bodies lose that quality when they are sufficiently heated
to become more or less conducting. Then, if a metal be in a large measure, or perhaps entirely, deprived of that
property, it should be capable of phosphorescence. Therefore it is quite possible that at some extremely high
frequency when behaving practically as a non-conductor, a metal or any other conductor might exhibit the quality
of phosphorescence, even though it be entirely incapable of phosphorescing under the impact of a low-frequency
discharge. There is, however, another possible way how a conductor might at least appear to phosphoresce.
Considerable doubt still exists as to what really is phosphorescence, and as to whether the various phenomena
comprised under this head are due to the same causes. Suppose that in an exhausted bulb, under the molecular
impact, the surface of a piece of metal or other conductor is rendered strongly luminous, but at the same time it is
found that it remains comparatively cool, would not this luminosity be called phosphorescence? Now such a result,
theoretically at least, is possible, for it is a mere question of potential or speed. Assume the potential of the elec-
trode, and consequently the speed of the projected atoms, ] to be sufficiently high, the surface of the metal piece ;
against which the atoms are projected would be rendered j highly incandescent, since the process of heat generation
| would be incomparably faster than that of radiating or 1 conducting away from the surface of the collision. In the
1 eye of the observer a single impact of the atoms would 1 cause an instantaneous flash, but if the impacts were
repeated with sufficient rapidity they would produce a continuous impression upon his retina. To him then the sur-
face of the metal would appear continuously incandescent and of constant luminous intensity, while in reality the
light would be either intermittent or at least changing periodically in intensity. The metal piece would rise in
temperature until equilibrium was attained--that is, until the energy continuously radiated would equal that
intermittently supplied. But the supplied energy might under such conditions not be sufficient to bring the body to
any more than a very moderate mean temperature, especially if the frequency of the atomic impacts be very low--
just enough that the fluctuation of the intensity of the light emitted could not be detected by the eye. The body
would now, owing to the manner in which the energy is supplied, emit a strong light, and yet be at a comparatively
very low mean temperature. How could the observer call the luminosity thus produced? Even if the analysis of the
light would teach him something definite, still he would probably rank it under the phenomena of phosphorescence.
It is conceivable that in such a way both conducting and non- . conducting bodies may be maintained at a certain

luminous intensity, but the energy required would very greatly vary with the nature and properties of the bodies.
These and some foregoing remarks of a speculative nature were made merely to bring out curious features of
alternate currents or electric impulses. By their help we may cause a body to emit more light, while at a certain
mean temperature, than it would emit if brought to that temperature by a steady supply; and, again, we may bring a
body to the point of fusion, and cause it to emit less light than when fused by the application of energy in ordinary
ways. It all depends on how we supply the energy, and what kind of vibrations we set up: in one case the vibrations
are more, in the other less, adapted to affect our sense of vision.
Some effects, which I had not observed before, obtained with carborundum in the first trials, I attributed to phos-
phorescence, but in subsequent experiments it appeared that it was devoid of that quality. The crystals possess a
noteworthy feature. In a bulb provided with a single electrode in the shape of a small circular metal disc, for
instance, at a certain degree of exhaustion the electrode is covered with a milky film, which is separated by a dark
space from the glow filling the bulb. When the metal disc is covered with carborundum crystals, the film is far
more intense, and snow-white. This I found later to be merely an effect of the bright surface of the crystals, for
when an aluminium electrode was highly polished it exhibited more or less the same phenomenon. I made a
number of experiments with the samples of crystals obtained, principally because it would have been of special
interest to find that they are capable of phosphorescence, on account of their being conducting. I could not produce
phosphorescence distinctly, but I must remark that a decisive opinion cannot be formed until other experimenters
have gone over the same ground.
The powder behaved in some experiments as though it contained alumina, but it did not exhibit with sufficient
distinctness the red of the latter. Its dead color brightens considerably under the molecular impact, but I am now
convinced it does not phosphoresce. Still, the tests with the powder are not conclusive, because powdered
carborundum probably does not behave like a phosphorescent sulphide, for example, which could be finely
powdered without impairing the phosphorescence, but rather like powdered ruby or diamond, and therefore it
would be necessary, in order to make a decisive test, to obtain it in a large lump and polish up the surface.
If the carborundum proves useful in connection with these and similar experiments, its chief value will be found in
the production of coatings, thin conductors, buttons, or other electrodes capable of withstanding extremely high
degrees of heat.
The production of a small electrode capable of withstanding enormous temperatures I regard as of the greatest im-
portance in. the manufacture of light. It would enable us to obtain, by means of currents of very high frequencies,
certainly 20 times, if not more, the quantity of light which is obtained in the present incandescent lamp by the same
expenditure of energy. This estimate may appear to many exaggerated, but in reality I think it is far from being so.
As this statement might be misunderstood I think it necessary to expose clearly the problem with which in this line
of work we are confronted, and the manner in which, in my opinion, a solution will be arrived at.
Anyone who begins a study of the problem will be apt to think that what is wanted in a lamp with an electrode is a
very high degree of incandescence of the electrode. There he will be mistaken. The high incandescence of the
button is a necessary evil, but what is really wanted is the high incandescence of the gas surrounding the button. In
other words, the problem in such a lamp is to bring a mass of gas to the highest possible incandescence. The higher
the incandescence, the quicker the mean vibration, the greater is the economy of the light production. But to
maintain a mass of gas at a high degree of incandescence in a glass vessel, it will always be necessary to keep the
incandescent mass away from the glass ; that is, to confine it as much as possible to the central portion of the globe.
In one of the experiments this evening a brush was produced at the end of a wire. This brush was a flame, a source
of heat and light. It did not emit much perceptible heat, nor did it glow with an intense light; but is it the less a
flame because it does not scorch my hand? Is it the less a flame because it does not hurt my eye by its brilliancy?
The problem is precisely to produce in the bulb such a flame, much smaller in size, but incomparably more power-
ful. Were there means at hand for producing electric impulses of a sufficiently high frequency, and for transmitting
them, the bulb could be done away with, unless it were used to protect the electrode, or to economize the energy by
confining the heat. But as such means are not at disposal, it becomes necessary to place the terminal in a bulb ' and
rarefy the air in the same. This is done merely to en- f able the apparatus to perform the work which it is not capable
of performing at ordinary air pressure. In the bulb we are able to intensify the action to any degree--so far that the
brush emits a powerful light.
The intensity of the light emitted depends principally on the frequency and potential of the impulses, and on the
electric density on the surface of the electrode. It is of the greatest importance to employ the smallest possible
button, in order to push the density very far. Under the violent impact of the molecules of the gas surrounding it,
the small electrode is of course brought to an extremely high temperature, but around it is a mass of highly

incandescent gas, a flame photosphere, many hundred times the volume of the electrode. With a diamond,
carborundum or zirconia button the photosphere can be as much as one thousand times the volume of the button.
Without much reflecting one would think that in pushing so far the incandescence of the electrode it would be
instantly volatilized. But after a careful consideration he would find that, theoretically, it should not occur, and in
this fact--which, however, is experimentally demonstrated--lies principally the future value of such a lamp.
At first, when the bombardment begins, most of the work is performed on the surface of the button, but when a
highly conducting photosphere is formed the button is comparatively relieved. The higher the incandescence of the
photosphere the more it approaches in conductivity to that of the electrode, and the more, therefore, the solid and
the gas form one conducting body. The consequence is that the further is forced the incandescence the more work,
comparatively, is performed on the gas, and the less on the electrode. The formation of a powerful photosphere is
consequently the very means for protecting the electrode, This protection, of course, is a relative one, and it should
not be thought that by pushing the incandescence higher the electrode is actually less deteriorated Still,
theoretically, with extreme frequencies, this result must be reached, but probably at a temperature too high for most
of the refractory bodies known. Given, then, an electrode which can withstand to a very high limit the effect of the
bombardment and outward strain, it would be safe no matter how much it is forced beyond that limit. In an
incandescent lamp quite different considerations apply. There the gas is not at all concerned: the whole of the work
is performed on the filament; and the life of the lamp diminishes so rapidly with the increase of the degree of
incandescence that economical reasons compel us to work it at a low incandescence. But if an incandescent lamp is
operated with currents of very high frequency, the action of the gas cannot be neglected, and the rules for the most
economical working must be considerably modified.
In order to bring such a lamp with one or two electrodes to a great perfection, it is necessary to employ impulses of
very high frequency. The high frequency secures, among others, two chief advantages, which have a most
important bearing upon the economy of the light production. First, the deterioration of the electrode is reduced by
reason of the fact that we employ a great many small impacts, instead of a few violent ones, which shatter quickly
the structure; secondly, the formation of a large photosphere is facilitated.
In order to reduce the deterioration of the electrode to the minimum, it is desirable that the vibration be harmonic,
for any suddenness hastens the process of destruction. An electrode lasts much longer when kept at incandescence
by currents, or impulses, obtained from a high-frequency alternator, which rise and fall more or less harmonically,
than by impulses obtained from a disruptive discharge coil. In the latter case there is no doubt that most of the
damage is done by the fundamental sudden discharges.
One of the elements of loss in such a lamp is the bombardment of the globe. As the potential is very high, the
molecules are projected with great speed ; they strike the glass, and usually excite a strong phosphorescence. The
effect produced is very pretty, but for economical reasons it would be perhaps preferable to prevent, or at least re-
duce to the minimum, the bombardment against the globe, as in such case it is, as a rule, not the object to excite
phosphorescence, and as some loss of energy results from the bombardment. This loss in the bulb is principally
dependent on the potential of the impulses and on the electric density on the surface of the electrode. In employing
very high frequencies the loss of energy by the bombardment is greatly reduced, for, first, the potential needed to
perform a given amount of work is much smaller; and, secondly, by producing a highly conducting photosphere
around the electrode, the same result is obtained as though the electrode were much larger, which is equivalent to a
smaller electric density. But be it by the diminution of the maximum potential or of the density, the gain is effected
in the same manner, namely, by avoiding violent shocks, which strain the glass much beyond its limit of elasticity.
If the frequency could be brought high enough the loss due to the imperfect elasticity of the glass would be entirely
negligible. The loss due to bombardment of the globe may, however, be reduced by using two electrodes instead of
one. In such case each of the electrodes may be connected to one of the terminals; or else, if it is preferable to use
only one wire, one electrode may be connected to one terminal and the other to the ground or to an insulated body
of some surface, as, for instance, a shade on the lamp. In the latter case, unless some judgment is used, one of the
electrodes might glow more intensely than the other.
But on the whole I find it preferable when using such high frequencies to employ only one electrode and one con-
necting wire. I am convinced that the illuminating device of the near future will not require for its operation more
than one lead, and, at any rate, it will have no leading-in wire, since the energy required can be as well transmitted
through the glass. In experimental bulbs the leading-in wire is most generally used on account of convenience, as in
employing condenser coatings in the manner indicated in Fig. 22, for example, there is some difficulty in fitting the
parts, but these difficulties would not exist if a great many bulbs were manufactured; otherwise the energy can be
conveyed through the glass as well as through a wire, and with these high frequencies the losses are very small.
Such illuminating devices will necessarily involve the use of very high potentials, and this, in the eyes of practical

men, might be an objectionable feature. Yet, in reality, high potentials are not objectionable -- certainly not in the
least as far as the safety of the devices is concerned.
There are two ways of rendering an electric appliance safe. One is to use low potentials, the other is to determine
the dimensions of the apparatus so that it is safe no matter how high a potential is used. Of the two the latter seems
to me the better way, for then the safety is absolute, unaffected by any possible combination of circumstances
which might render even a low-potential appliance dangerous to life and property. But the practical conditions
require not only the judicious determination of the dimensions of the apparatus ; they likewise necessitate the
employment of energy of the proper kind. It is easy, for instance, to construct a transformer capable of giving,
when operated from an ordinary alternate current machine of low tension, say 50,000 volts, which might be
required to light a highly exhausted phosphorescent tube, so that, in spite of the high potential, it is perfectly safe,
the shock from it producing no inconvenience. Still, such a transformer would be expensive, and in itself
inefficient; and, besides, what energy was obtained from it would not be economically used for the production of
light. The economy demands the employment of energy in the form of extremely rapid vibrations. The problem of
producing light has been likened to that of maintaining a certain high-pitch note by means of a bell. It should be
said a barely audible note; and even these words would not express it, so wonderful is the sensitiveness of the eye.
We may deliver powerful blows at long intervals, waste a good deal of energy, and still not get what we want; or
we may keep up the note by delivering frequent gentle taps, and get nearer to the object sought by the expenditure
of much less energy. In the production of light, as far as the illuminating device is concerned, there can be only one
rule--that is, to use as high frequencies as can be obtained; but the means for the production and conveyance of
impulses of such character impose, at present at least, great limitations. Once it is decided to use very high
frequencies, the return wire becomes unnecessary, and all the appliances are simplified. By the use of obvious
means the same result is obtained as though the return wire were used. It is sufficient for this purpose to bring in
contact with the bulb, or merely in the vicinity of the same, an insulated body of some surface. The surface need, of
course, be the smaller, the higher the frequency and potential used, and necessarily, also, the higher the economy of
the lamp or other device.
This plan of working has been resorted to on several occasions this evening. So, for instance, when the incandes-
cence of a button was produced by grasping the bulb with the hand, the body of the experimenter merely served to
intensify the action. The bulb used was similar to that illustrated in Fig. 19, and the coil was excited to a small po-
tential, not sufficient to bring the button to incandescence when the bulb was hanging from the wire; and incident-
ally, in order to perform the experiment in a more suitable manner, the button was taken so large that a perceptible
time had to elapse before, upon grasping the bulb, it could be rendered incandescent. The contact with the bulb
was, of course, quite-unnecessary. It is easy, by using a rather large bulb with an exceedingly small electrode, to
adjust the conditions so that the latter is brought to bright incandescence by the mere approach of the experimenter
within a few feet of the bulb, and that the incandescence subsides upon his receding.
In another experiment, when phosphorescence was excited, a similar bulb was used. Here again, originally, the
potential was not sufficient to excite phosphorescence until the action was intensified--in this case, however) to
present a different feature, by touching the socket with a metallic object held in the hand. The electrode in the bulb
was a carbon button so large that it could not be brought to incandescence, and thereby spoil the effect produced by
Again, in another of the early experiments, a bulb was used as illustrated in Fig. 13. In this instance, by touching
the bulb with one or two fingers, one or two shadows of the stem inside were projected against the glass, the touch
of the finger producing the same result as the application of an external negative electrode under ordinary
In all these experiments the action was intensified by augmenting the capacity at the end of the lead connected to
the terminal. As a rule, it is not necessary to resort to such means, and would be quite unnecessary with still higher
frequencies ; but when it is desired, the bulb, or tube, can be easily adapted to the purpose.
In Fig. 24, for example, an experimental bulb L is shown, which is provided with a neck n on the top for the appli-
cation of an external tinfoil coating, which may be connected to a body of larger surface. Such a lamp as illustrated
in Fig. 25 may also be lighted by connecting the tinfoil coating on the neck n to the terminal, and the leading-in
wire to to an insulated plate. If the bulb stands in a socket upright, as shown in the cut, a shade of conducting
Material may be slipped in the neck n, and the action thus magnified.




A more perfected arrangement used in some of these bulbs is illustrated in Fig. 26. In this case the construction of
the bulb is as shown and described before, when reference was made to Fig. 19. A zinc sheet Z, with a tubular
extension T, is slipped over the metallic socket S. The bulb hangs downward from the terminal, the zinc sheet Z,
performing the double office of intensifier and reflector. The reflector is separated from the terminal t by an exten-
sion of the insulating plug P. A similar disposition with a phosphorescent tube is illustrated in Fig. 27. The tube T is
prepared from two short tubes of a different diameter, which are sealed on the ends. On the lower end is placed an
outside conducting coating Q which connects to the wire w. The wire has a hook on the upper end for suspension,
and passes through the centre of the inside tube, which is filled with some good and tightly packed insulator. On the
outside of the upper end of the tube T is another conducting coating C,, upon which is slipped a metallic reflector
Z, which should be separated by a thick insulation from the end of wire w.

The economical use of such a reflector or intensifier would require that all energy supplied to an air condenser
should be recoverable, or, in other words, that there should not be any losses, neither in the gaseous medium nor
through its action elsewhere. This is far from being so, but, fortunately, the losses may be reduced to anything
desired. A few remarks are necessary on this subject, in order to make the experiences gathered in the course of
these investigations perfectly clear.
Suppose a small helix with many well insulated turns, as in experiment Fig. 17, has one of its ends connected to
one of the terminals of the induction coil, and the other to a metal plate, or, for the sake of simplicity, a sphere,
insulated in space. When the coil is set to work, the potential of the sphere is alternated, and the small helix now
behaves as though its free end were connected to the other terminal of the induction coil. If an iron rod be held
within the small helix it is quickly brought to a high temperature, indicating the passage of a strong current through
the helix. How does the insulated sphere act in this case?
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 molecules, 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
alternating, 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
frequencies and more or less high potentials are used, the loss may be very great. The total energy lost per unit of
time is proportionate 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 imparted to the molecule is proportionate to that density. I conclude from this that the total energy
lost must be proportionate to the product of the frequency and the square of the electric density ; but this law needs
experimental confirmation. Assuming the preceding considerations to be true, then, by rapidly alternating the
potential of a body immersed 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 violations--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 currents
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.
When energy is absorbed in a condenser the same behaves 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, necessarily 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 condenser 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 investigators. 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 tinfoil coatings are large, close together, and the charged
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 principally 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 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 imperfect 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
condenser. 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 impacts
and collisions, and pass off into space in the form of short heat, and possibly light, waves. As both the frequency 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 atmosphere in various places, the effect produced would accordingly
vary from place to place. Considerable variations 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 sudden, 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 important factor of loss the air in the 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 frequency, 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 displacements, 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 obviously of advantage in such a lamp to confine as much as
possible the heat to the electrode by preventing the circulation 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
required 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 the small bulb b to slip through. Otherwise the construction is the same as shown in Fig. 18, for example.
The small bulb is conveniently supported upon the stem s, carrying 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 c f
the aluminium tube upon a sudden turning on of the current. 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 arrangement
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 making 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
m, upon being exhausted to a very high degree was sealed in a large globe L, which was then moderately exhausted
and sealed off. The principal advantage of this construction was that it allowed of reaching extremely high vacuum,
and, at the same time use a large bulb. It was found, m 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
only just enough to allow the discharge to pass through and the space between the bulbs appeared crimson,
producing a curious effect. In some cases, when the exhaustion in globe L was very low, and the air good
conducting it was found necessary, in order to bring the button m to high incandescence, to place, preferably on the
upper part of the neck of the globe, a tinfoil coating which was connected to an insulated body, to the ground, or to
the other terminal of the coil, as the highly conducting air weakened 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 comparatively 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 terminal. 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
frequencies 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
number of the impulses being augmented, the potential energy of each would diminish, so that finally only atomic
vibrations could be set up, and the motion of translation through durable space would cease. Thus an ordinary gas
burner 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 increase 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.

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