Nikola Tesla: Colorado Springs Notes, 1899-1900 Image IX (9)

IX. This photograph illustrates again the extra coil with streamers and sparks from a pointed wire placed towards the camera. The wire or terminal was turned slightly downwards to cause the streamers or sparks to go more downward, as there was a considerable danger in this experiment of inflaming the roof of the building by the discharge taking an upward course. The streamers, when made to issue from a point as in this instance, are namely very long and in fact it was found impossible to work the apparatus to its full capacity in this account. The excitation of the “extra coil” system was pushed as far as could be done without great risk. The longest streamers reached the side of the building and even the corners sometimes. One of them reached the photographer Mr. Alley in the corner of the building, while another one struck me as I was operating the switch in another corner. They were so feeble at that distance, however, that they did not cause any injury or pain. Another one struck the camera but, as subsequently found, did not spoil the plate. These streamers were about the longest produceable in the present building, with the roof closed, measuring from 31 - 32 feet in a straight line from origin to end. Taking into account the curiously curved path the length was probably more than twice this, so that taking the discharge from tip to tip of these longest streamers, the actual path of the discharge through the air was from, say, 124 - 128 feet! If the building would permit I think that with the present apparatus, by putting about two to three times the copper in the oscillator a discharge extending through approximately twice this distance would be obtained, and by overcoming some defects of the present type of oscillator a further gain of about 50% could still be effected, so that I can certainly expect to reach, measured in this way, a length from 372 to 384 feet from end to end. In an industrial plant

it seems to me advisable to push the pressure still further and the difficulties in this respect do not seem to me now to be very great. In the present photograph certain features before commented upon are even better shown than in the preceding plates. For instance, the high luminosity on the bottom where a spark strikes the floor, the “splashing” of the discharge, the branching out and the interruption of a streamer are all well shown. But the most curious feature is the appearance of “fire balls”. As already noted in a previous instance a streamer even when not as strong as these here described, will show sometimes one or more points of greater luminosity than the rest. On a plate an effect of this kind may be produced by a streamer suddenly bending or turning, but the actual appearance of these luminous spots or points is unmistakable. In the instance here described the streamers were very powerful and the spots when they appeared were about an inch or possibly more in diameter, actual “fire balls” as they appeared to the eye. Now what is the cause of their formation? I attribute them to the presence of some material in the air at that particular spot which is of such a nature that when heated it increases the luminosity. It is possible that sodium is concerned in the production of the phenomenon. But the luminous “ball” must be extremely short lived as it does not impress itself upon the plate sufficiently despite its high luminosity. One can barely note a small luminous patch on the streamer, the impression of the central portion of the “ball”. It is not improbable that the evolution of the “fire ball” may be connected with a process akin to explosion or sudden volatilization. Again, in this instance the same kind of plate was used and the vibration of the extra coil was but slightly quicker than normal.

In plates VII, VIII and IX one hundred closures of the switch were made.