Hewitt-Sperry Automatic Airplane for eight years, and yet Sperry became intrigued with the concept of applying radio control to them. He realized that for radio control to be effective, automatic stabilization would be essential, so he decided to adapt his naval gyro-stabilizers (which he had developed for destroyers). In 1913, the Navy provided a flying boat to test and evaluate the gyro-based autopilot. Sperry's son Lawrence served as an engineer during the test phase. In 1914, Lawrence Sperry was in Europe and observed the developing techniques of aerial warfare, including the use of aircraft. In 1916, the two Sperrys joined Peter Hewitt, an
Invention of the telephone receiver. Gray did not convert his caveat into a patent application until after the caveat had expired and hence left the field open to Bell. When Gray applied for a patent for the variable resistance telephone transmitter, the Patent Office determined "while Gray was undoubtedly the first to conceive of and disclose the (variable resistance) invention, as in his caveat of 14 February 1876, his failure to take any action amounting to completion until others had demonstrated the utility of the invention deprives him of the right to have it considered." The carbon microphone was independently developed around 1878 by