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INVENTIONS OF NIKOLA TESLA.

Such a damaging break would not occur with a steady force, evenif the same were many times greater. The break is due to theagitation of the molecules of the gas within the bulb, and outsideof the same. This agitation, which is generally most violent inthe narrow pointed channel near the seal, causes a heating andrupture of the glass. This rupture, would, however, not occur,not even with a varying force, if the medium filling the inside ofthe bulb, and that surrounding it, were perfectly homogeneous.The break occurs much quicker if the top of the bulb is drawnout into a fine fibre. In bulbs used with these coils such nar-row, pointed channels must therefore be avoided.

When a conducting body is immersed in air, or similar insulat-ing medium, consisting of, or containing, small freely movableparticles capable of being electrified, and when the electrificationof the body is made to undergo a very rapid change—which isequivalent to saying that the electrostatic force acting aroundthe body is varying in intensity,—the small particles are attractedand repelled, and their violent impacts against the body maycause a mechanical motion of the latter. Phenomena of thiskind are noteworthy, inasmuch as they have not been observedbefore with apparatus such as has been commonly in use. If avery light conducting sphere be suspended on an exceedingly finewire, and charged to a steady potential, however high, the spherewill remain at rest. Even if the potential would be rapidlyvarying, provided that the small particles of matter, molecules oratoms, are evenly distributed, no motion of the sphere should re-sult. But if one side of the conducting sphere is covered with athick insulating layer, the impacts of the particles will cause thesphere to move about, generally in irregular curves, Fig. 172a.In like manner, as I have shown on a previous occasion, a fan ofsheet metal, Fig. 1725, covered partially with insulating materialas indicated, and placed upon the terminal of the coil so as to turnfreely on it, is spun around..

All these phenomena you have witnessed and others whichwill be shown later, are due to the presence of a medium likeair, and would not occur in a continuous medium. The actionof the air may be illustrated still better by the following experi-ment. I take a glass tube t , Fig. 173, of about an inch in di-ameter, which has a platinum wire w sealed in the lower end,and to which is attached a thin lamp filament f. I connect thewire with the terminal of the coil and set the coil to work. The