The Bob Moog Foundation's, MARC DOTY, has posted a video to YouTube in which he states that French inventor Maurice Martenot met Leon Theremin, was inspired by him, and because of that he went on to invent the ondes martenot.
This is wrong.
The theremin and the ondes were invented entirely independently of one another, and Lev Termen and Maurice Martenot did not meet until a brief encounter in 1927 when Lev was in Paris introducing his instrument to the French public. By that time, the first generation ondes had already been built and it was introduced just a few months later on the same stage where the theremin had been demonstrated.
The interesting question is: which instrument was invented first? The ondes or the theremin?
There is good reason to believe that the ondes was conceived before the theremin because Maurice Martenot was publicly demonstrating the heterodyne phenomenon to his fellow soldiers in the French army prior to the end of World War One (1914 - 1918). Martenot was a radio operator, and he would amuse the troops in his spare time by playing tunes "gesturally" using his radio equipment, and would broadcast the melodies from the loudspeaker on the truck (le petit camion gris) that carried his mobile wireless equipment.
Martenot's biographer, Jean Laurendeau (MAURICE MARTENOT: LUTHIER DE L'ELECTRONIQUE) says the sound was compared by some who heard it to a wailing chihuahua, so the "instrument" was dubbed "the Mexican dog" (le chien méxicain). We are told that Martenot played simple, familiar melodies like AU CLAIR DE LA LUNE.
Lev Termen, according to his biographer Albert Glinsky, did not begin experimenting with the possibilities afforded by Lee De Forest's audion tubes until sometime around 1920 when Lev went to work for Abram Ioffe at the Physico-Technical Institute in St. Petersburg. This means that the concept of making music using the heterodyne principle was first explored by Martenot as much as two years before Lev Termen had the same idea. It also seems that the discovery of the heterodyne phenomenon itself was serendipitous on the part of both Martenot and Termen, and neither would have discovered it at all had it not been for De Forest's invention of 1906.
Martenot and Termen met again in America in the 1930's, and great hopes were entertained for their collaboration and the future of music, but nothing ever came of their encounters.
The fact is, Martenot did not believe that the theremin was viable as a musical instrument because it was too limited in regard to what it could do, and much too difficult to control with accuracy and precision. The first generation ondes was very theremin-like, but Martenot abandoned the concept and went on to devise an instrument similar to the so-called "tannerin" of the late Paul Tanner. Following that, he added a floating keyboard to the instrument and a toggle that allowed the player to switch easily from "ribbon control" to "keyboard control".
Unfortunately, the instrument was doomed by the great expense of manufacturing. When Martenot died in 1980, he left the business to his sons who promptly went bankrupt!
Efforts have been made to revive the ondes but it has been an uphill battle because of the availability of a wide variety of highly versatile modern synthesizers and ribbon control devices.