Nikola Tesla U.S. Patent 649,621 - Apparatus for Transmission of Electrical Energy Patent Wrapper Page 7

204 2 length wound around and in proximity to the coil A. p The apparatus at one point is used as a transmitter, the coil A in this case. constituting a high tension secondary, and the coil C, the primary of much lower tention of a transformer. In the circuit of the primary C is included a suitable source of current G. One terminal of the secondary A, is at the center of the spiral coil, and from this terminal the current is led by a conductor B to a terminal D, preferable of large surface, formed or maintained by such means as a balloon at an elevation suitable for the purposes of transmission. The other terminal of the secondary A is connected to earth and, if desired, to the primary also, in order that the latter may be at substantially the same potential as the adjacent portions of the secondary, thus insuring safety. At the receiving station a transformer of similar construction is employed, but in this case the longer coil A' constitutes the primary, and the shorter coil C the secondary of the transformer. In the circuit of the latter are connected lamps L, motors M, or other devices for utilizing the current. The elevated terminal D' connects with the center of the coil A' and the other terminal of said coil is connected to earth and, preferably, also to the coil C' for the reasons above stated. Q The length of the thin wire coil in each transformer should be approximately one-quarter of the wave 2