The "Biefeld–Brown effect" was the name given to a phenomenon observed by Thomas Townsend Brown while he was experimenting with X-ray tubes during the 1920s while he was still in high school. When he applied a high voltage electrical charge to a Coolidge tube that he placed on a scale, Brown noticed a difference in the tube's mass depending on orientation, implying some kind of net force. This discovery caused him to assume that he had somehow influenced gravity electronically and led him to design a propulsion system based on this phenomenon. On 15 April 1927, he applied for a patent, entitled "Method of Producing Force or Motion," that described his invention as an electrical-based method that could control gravity to produce linear force or motion. In 1929, Brown published an article for the popular American magazine Science and Invention, which detailed his work. The article also mentioned the "gravitator," an invention by Brown which produced motion without the use of electromagnetism, gears, propellers, or wheels, but instead using the principles of what he called "electro-gravitation." He also claimed that the asymmetric capacitors were capable of generating mysterious fields that interacted with the Earth's gravitational pull and envisioned a future where gravitators would propel ocean liners and even space cars.