Some of Tesla's Experiments Simplified

Editor's note: Commentary on this article can be found at; Some of Tesla's Experiments Simplified - Commentary 1, Some of Tesla's Experiments Simplified - Commentary 2 and Some of Tesla's Experiments Simplified - To F. E. P.

Although six months have elapsed since Nikola Tesla's epoch-making lecture at the Royal Institution, the extraordinary interest excited by his experiments has in no way declined, and there are few who take any practical part in electricity, whether as amateurs or professionals, but have longed to produce for themselves some of the wonderful phenomena which he dealt with so cleverly and withal as modestly. As Lord Rayleigh said, he has "given us food for intellectual contemplation for a long time to come"; but we are not content to contemplate — we want to imitate. Our imaginations have been quickened, and if we cannot go forward on our own account, we at least want to keep pace. Few will have at hand the necessary appliances used by Tesla in producing the brilliant effects which were the wonder of those who were privileged to witness them last February. Hence, we feel sure that our readers will be gratified to learn that, owing to the recent researches of Mons. Andrea Giulio Rossi, it has been discovered that many of Tesla's experiments can be reproduced by means of apparatus which everyone who "dabbles in electricity," or practises it as a profession, have at hand.

Tesla used an induction coil of a special form, and passed through its primary coil a special oscillatory current in producing high frequency and high potential. The current was sent from an alternating dynamo into the primary of a transformer, the secondary being connected through a magneto-static interrupter to two brass knobs, between which a series of discharges takes place. From these knobs were taken leads to the primary terminals of an induction coil, not directly, however, but through a capacity formed by Leyden jars. It is thus seen that when a spark occurs at the brass knobs an oscillatory discharge surges through the added capacity to the primary of the induction coil. The rate of the oscillation is about one million per second.

One of the most curious and astonishing of the experiments performed by Tesla with this current was to touch the poles of his apparatus with one hand whilst he held a Geissler tube in the other, the latter being instantaneously illuminated. This can be reproduced, so M. Rossi tells us, with a simple Rhumkorff coil.

A coil which would give sparks from five to six centimètres long was employed by Rossi, and he used a current of high period, but having by no means the number of alternations per second which characterised that used by Tesla. On placing one hand on one of the poles of the coil, and holding a Geissler tube in the other hand, the tube became luminous, though not very brilliantly luminous. This luminosity was manifested, too, even when two or three persons joined their hands, the first touching the coil, whilst the third held the tube.

A Geissler tube was illuminated by merely placing it near one of the terminals of the Rhumkorff coil. The light was more intense near the centre of the tube if the latter was isolated; but if held in the hand, the whole of the interior was suffused by an intense glow. the tube became completely luminous also if connected to earth, and not touched by the hand.

Another experiment performed by Rossi was as follows: An insulated Geissler tube was placed at a short distance from the coil, the poles of the latter not being connected. If it were held perpendicular to the generating line of the cylinder (coil), the light, which was evident in the opposite position, disappeared.

The elimination of electrodes in the Geissler tube did not appear to affect the general result. Rossi constructed a tube about a yard long, in which he made a vacuum, then filled it with water vapour, and finally absorbed the latter by means of potash. The tube, when held in the hand near the coil, became brilliantly illuminated. Moreover, by insulating the tube, and then placing it about a yard from the coil, in such a position that the prolongation of its axis would impinge upon one of the poles of the coil, the same result was obtained; but the glow was intensified by approaching the foot towards the tube, whilst one of the hands grasps the other terminal of the coil. 

Mons. Rossi considers that these experiments may be performed by anyone who possesses this simple apparatus, and that, in all probability, Tesla may be imitated on the small scale by equally simple means. No doubt some of our readers will test this for themselves.