Smithsonian Report, 1924. — Wliitney 



Plate 3 



A Deivionstration of the Action of a Photo-Electric 

 Cell Connected Through a Relay to an Incandescent 

 Lamp. When No Light Falls on the Cell, the Lamp 

 BURNS; When the Cell Is Exposed to Light, the 

 Lamp Is Extinguished 



2. Apparatus Consisting of a Photo-Electric Cell, Indicating Lamps, 

 Capacities and Amplifiers (in Box), and a Doorbell Arranged to De- 

 monstrate THE Retarded Transmission of an Impulse, Such as Nerve 

 Action 



o 



^ 



3. Three Suspended Rubber Bal- 

 loons Repelling Each Other to 

 A Triangular Formation as the 

 Result of Being Electrostati- 

 cally Charged. (See Fig. I, PL. 4) 



