Some of Tesla's Experiments Simplified

[33984.] — While experimenting with an induction coil some time ago; I succeeded in producing an effect which I have never seen described, and if it be a real novelty, will probably be interesting to readers of the "E. M." The effect in question was produced by placing an electric incandescent lamp between the secondary terminals of the coil, when the bulb was instantly illuminated with a strong blue glow. It is necessary to state that the filament of the lamp had been broken off, the vacuum being still maintained. I was struck by the experiment, and tried an uninjured lamp in the same position, but could get no result with it. I then took the former lamp and covered half the bulb (the part farthest from the lamp terminals) with tinfoil, pasting it on carefully. The result when tried with the coil was almost magical. The finest effect was got by connecting the lamp terminals to one terminal of the coil, the other being connected to the tinfoil on lamp. A brilliant effect could also be produced by connecting the lamp to one coil terminal while any earth-connected conductor was allowed to touch the tinfoil. Finally I found that it was quite sufficient to hold the lamp in the hand at a distance of as much as a yard from the coil, whilst the latter was working, to get a good effect. No doubt the action of the lamp was similar to that of a vacuum tube; but it should be remembered that in the case of the lamp, only one conductor penetrated into the interior of the bulb. I should mention that the coil was built to produce ¼in. sparks, and is well-made and insulated.

An idea suggested by one of, Tesla's experiments is to pass the secondary current from one coil into the primary of a second coil, in order to produce sparks of a considerable length. I have had no chance of trying this arrangement yet. I would suggest that the insulation of the second ooil should be perfection, and that perhaps a condenser would be advantageous. If the arrangement were workable, it is evident that long sparks might be obtained from a couple of small coils, costing together considerably less than one constructed to give the whole spark outright.

F. E. P.

Some of Tesla's Experiments Simplified — To "F.E.P."

[33991.] — The effects narrated are well known, and are simply proofs of the extent to which the lines of inductive force penetrate the surrounding air.

With reference to the coils connected in series, this also has been done. Of course, the second coil, as it is supplied with an alternating current from the first one, does not need, and, in point of fact, must not have, a contact breaker. Also it is necessary, in order to get good effects, that the primary of the second coil should consist of wire as fine as that of the secondary of the first coil, and that the insulation should be of the most perfect kind. In some experiments detailed a month or so ago in the pages of "Ours," the coil was immersed bodily in resin oil. This second coil is in reality a transformer, and what is gained in E.M.F. is lost in current.

S. Bottone

[33992.] — More than a year ago I made, quite by chance, exactly the same experiment as "F.E.P." relates in letter 33984, with the exception that my lamp was quite sound. I was trying to light a lamp with an induction coil, and, not succeeding, probably because there were not enough ampères, I took off one of the wires from the lamp terminal, when suddenly, on my accidentally touching with the wire the spring of the lamp's socket, the lamp lit up a phosphorescent bluish glow, a little darker near the filament. The same thing occurred in touching the glass bulb with even the isolated portion of the wire from the induction coil; but the greatest brilliancy was obtained when the electrode was terminated by a large metallic surface. I repeated the experiment the next day, but have not been able to repeat it again.

One day, however, my lamp — always perfectly sound — was lying close to one of the electrodes of the induction coil, when on completing the secondary circuit the lamp gave a bluish glow as before, but this time of equal intensity in every part. I never could repeat the experiment. The lamp is a 10-candle one, and the coil gives a 3-millimètre spark.

L. Demengel