The Hammond organ was introduced in US Patent 1,956,350. A difference between the Hammond organ and Telharmonium is that Telharmonium tones were something like ``bandlimited square wave'' tones (see Fig.G.1), while the Hammond organ tone wheels were carefully machined to provide nearly sinusoidal components. Thus, the Hammond organ truly classifies as an ``additive synthesis device'' (§G.8). It has survived essentially intact to the present day, and has been extensively simulated electronically (e.g., in Korg synthesizers).
Dudley's Channel Vocoder
Early Additive Synthesis in Film Making