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.