LOUDNESS 



429 



MOTOR 



Fig. 22 — Schematic of optical tone generator. 



The desired wave form was accurately drawn on a large scale and 

 then transferred photographically to the glass disk designated as D in 

 the diagram. The disk, driven by a motor, rotated between the lamp 

 L and a photoelectric cell C, producing a fluctuating light source which 



Fig. 23 — Ten disk optical tone generator. 



