the fantastic inventions of nikola tesla - Exopolitics Hong Kong

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 important,
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