Nikola Tesla U.S. Patent 645,576 - System of Transmission of Electrical Energy Patent Wrapper Page 52

170 to a high temperature; Second, that the conductivity imparted to the air or gases increases very rapidly, both with the augmentation of the applied electrical pressure and with the degree of rarefaction, the law in this latter respect being, however, quite different from that heretofore established. In illustration of these facts a few observations, which 2/ I have made with apparatus devised for the purposes here contemplated, may be cited. For example, a conductor or terminal, to which impulses such as those here considered are supplied, but which is otherwise insulated in space and is remote from any conducting bodies, is surrounded by a luminous, flame-like brush or discharge, often covering many hundreds or even as much as several thousands of square feet of surface, this striking phenomenon clearly attesting the high degree of conductivity which the atmosphere attains under the influence of the immense electrical stresses to which it is subjected. This influence is, however, not confined to that portion of the atmosphere, which is discernible by the eye as luminous and which, as has been the case in some instances actually observed, may fill the space within a spherical or cylindrical envelope of a diameter of sixty feet or more, but reaches out to far remote regions, the insulating qualities of the air being, as I have ascertained, still sensibly impaired at a distance many hundred times that, through which the luminous discharge projects from the terminal and, in all probability, much farther. The distance extends with the increase of the electro-motive force of the impulses, with the diminution of the density of the atmosphere, with the elevation of the active. -3This page retyped from microfilm for better readability - Ed.]