When vibrations of speech impinged upon the resonant surface its rhythmic light-vibrations were broken, just as a telephone transmitter breaks an electric current.

Simultaneously these light-vibrations were changed into sound--on the surfaces of all spheres tuned to that particular instrument.

The "crawling" colours which showed themselves at these times were literally the voice of the speaker in its spectrum equivalent.

While usually the sounds produced required considerable familiarity with the apparatus to be understood quickly, they could, on occasion, be made startlingly loud and clear--as I was soon to realize--W.

T.G..