Mahlon Loomis (21 July 1826 – 13 October 1886) was an American dentist and inventor.
He is best known for promoting the idea that the Earth's upper atmosphere was divided into discrete concentric layers, and these layers could be tapped by metallic conductors on hills and mountain tops, in order to provide long-distance wireless telegraph and telephone communication, as well as draw electricity down to the Earth's surface.
His idea of conductive atmospheric layers has been discredited.
However, based on his claims of successful wireless telegraphic and telephonic transmissions in the 1860s and 1870s, it is sometimes asserted that Loomis' equipment had, inadvertently, been the first to produce and receive radio signals.