high-voltage terminal often strike the primary winding of the coil. This momentarily creates a conductive path for the lethal 50/60 Hz primary current from the supply transformer to reach the output terminal. If a person is connected to the output terminal at the time, either by touching it or allowing arcs from the terminal to strike the person's body, then the high primary current could pass through the conductive ionized air path, through the body to ground, causing electrocution. Skin-effect myth An erroneous explanation for the absence of electric shock that has persisted among Tesla coil hobbyists is that the high-frequency currents travel through the body close to the surface, and thus do not penetrate to vital organs or nerves, due to an electromagnetic phenomenon called skin effect. This theory is false. RF current does tend to flow on the surface of conductors due to skin effect, but the depth to which it penetrates, called skin depth, depends on the resistivity and permeability of the material as well as the frequency. Although skin effect limits currents of Tesla coil frequencies to the outer fraction of a millimeter in metal conductors, the skin depth of the current in body tissue is much deeper due to its higher resistivity. The depth of penetration of currents of Tesla frequency (0.1 – 1 MHz) in human tissues is roughly 24 to 72 centimeters (9 to 28 inches). Since even the deepest tissues are closer than this to the surface, skin effect has little influence on the path of the current through the body; it tends to take the path of minimum electrical impedance to ground, and can easily pass through the core of the body. In the medical therapy called longwave diathermy, carefully controlled RF current of Tesla frequencies was used for decades for deep tissue warming, including heating internal organs such as the lungs. Modern shortwave diathermy machines use a higher frequency of 27 MHz, which would have a correspondingly smaller skin depth, yet these frequencies are still able to penetrate deep body tissues. Related patents Tesla's patents "Electrical Transformer Or Induction Device". U.S. Patent No. 433,702, August 5, 1890 "Means for Generating Electric Currents", U.S. Patent No. 514,168, February 6, 1894 "Electrical Transformer", Patent No. 593,138, November 2, 1897 "Method Of Utilizing Radiant Energy", Patent No. 685,958 November 5, 1901 "Method of Signaling", U.S. Patent No. 723,188, March 17, 1903 "System of