Nikola Tesla U.S. Patent 645,576 - System of Transmission of Electrical Energy Patent Wrapper Page 42

160 Substitute Sub Speein Fr.27-97 Sub A To all whom it may concern:- Be it known that I, Nikola Tesla, a citizen of the United States, residing at New York, in the County and State of New York, have invented certain new and useful improvements in Systems of Transmission of Electrical Energy, of which the following is a specification, refence being had to the drawing accompanying and forming a part of the same. It has been well known, heretofore, that by rarefying the air enclosed in a vessel its insulating properties are impaired to such extent that it becomes what may be considered as a true conductor, al though one of admitedly very high resistance. The practical information on this subject has been derived from observations manifestly subject to limitations imposed by the character of the apparatus, or means heretofore known, and the quality of the electrical effects producible thereby. It is indispensa ble for the attainment of the results contemplated in the invention or discovery upon which my present application is based that both the latter, that is, the means and effects, should be èssentially different in their characteristics and actions from those before used and investigated. To be more explicit, while it has been heretofore possible, by means of the apparatus at command to produce only moderate electrical pressures, and even these not without some risks and difficul1 ty, I have devised means whereby I am enabled to gener! ate with safety and ease electrical pressures measured -1