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INVENTIONS OF NIKOLA TESLA.

is best performed with a highly exhausted and freshly made tube."When the tube has been used for some time the experimentoften fails. It is possible that the gradual and slow impairmentof the vacuum is the cause. This slow propagation of the dis-charge through a very narrow glass tube corresponds exactly tothe propagation of heat through a bar warmed at one end. Thequicker the heat is carried away laterally the longer time it willtake for the heat to warm the remote end. When the currentof a low frequency coil is passed through the fibre from end toend, then the lateral dissipation is small and the discharge in-stantly breaks through almost without exception.

Fig. 189. Fig. 190.

After these experiments and observations which have shownthe importance of the discontinuity or atomic structure of themedium and which will serve to explain, in a measure at least,the nature of the four kinds of light effects producible withthese currents, I may now give you an illustration of theseeffects. For the sake of interest I may do this in a mannerwhich to many of you might be novel. You have seen beforethat we may now convey the electric vibration to a body bymeans of a single wire or conductor of any kind. Since the