Nikola Tesla: Colorado Springs Notes, 1899-1900 Image LXII (62)

LXII. This is one of the most beautiful plates taken. It shows a discharge issuing from the base of a cone upon which a ball of 30" diameter is resting. Streamers, though a few only, issue also from the ball giving evidence of the immense electrical pressure and quantity of electric movement. It was indispensable to employ the metallic conical vessel for the purpose of preventing the discharge from following the wooden support, upon which the ball of 30" was supported, to the ground. This would unavoidable occur even if the support were of the most excellent material as regards insulation, as of glass for example, and no matter how high the support might be.

In fact, I have found from long experience with these discharges of extreme electromotive force, that it is almost impossible to insulate a terminal without some such provision as used in the present instance. The fundamental idea is to provide an arrangement such that the place of support, or that part of the terminal which rests upon the support, is guarded by the conductor projecting beyond. In other words the terminal must be resting on the support on points where there is no electrical pressure or, at any rate, a very small pressure. This amounts to screening the support statically. Another way to prevent the current from following the support is to place a coil, through which the current passes, beneath the support passing axially through the coil. The hood, referred to repeatedly in these descriptions, is used for the same purpose as without the same the current would pass along the pole to the ground. But the hood might be dispensed with by using an extra coil of much smaller diameter, axial with the wooden pole supporting the iron structure, but it would be necessary for insuring safety to let the coil finish very close to the bottom of the iron structure where it rests upon the insulating support. This has been one of the great difficulties encountered in the course of this work and it has required much time

and trouble to overcome it successfully. For the same purposes also the large hood, above the cords keeping the iron pole in position, is employed. The rims of both these hoods are curved so as to enable a greater pressure to be reached by preventing the streamers to break out into the air easily and at a much smaller pressure. In a new apparatus, now under consideration, these improvements will be carried much further and I am confident to obtain results far beyond anything arrived at so far.

In the present experiment it is rather astonishing to see some streamers breaking out from the surface of the ball of such a large radius of curvature, when they can pass out so easily from the edge or base of the cone underneath. This shows the existence of violent surgings and a great quantity of electricity set in motion in the system. The photograph shows some luminous spots on a very powerful streamer passing to the floor. Many sparks are very curious on account of the curved paths they follow. The streamers here are also mostly of fine texture, this being due to the facility with which they break forth from the edge of the inverted pass and to their abundance. It may be seen from the plate that one of the supports of the extra coil caught fire. The particulars in this experiment were as in most cases before, 100 throws of the switch being made.