338 Mr. Otto Stuhlmann on a Difference in Photoelectric 



from the normal, on the part of the plates, would affect the 

 results. A change of five degrees in the position of the 



Fiff. 4. 





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.9+ .98 l-OZ 1.0C A/0 



Ratio o^ EmeYQent to Incident EvVect. 



plates showed no measurable effect. Blank quartz plates 

 placed in the cylinders gave negative results. A test for 

 photoelectric effects arising from scattered light gave no 

 measurable effects, since the aim in the design of the appa- 

 ratus was to use so small a beam that it cleared all openings 

 in the apparatus and the reflected beams passed out, back 

 through the openings, through which the incident beam 

 entered. 



An attempt was made to estimate the absolute value 

 of the thickness of the thin films used, by measuring 

 their resistance. For this purpose " Set 2 " of the above 

 data was used. In order to get proper electrical connexions 

 the two opposite edges of the film were silvered by means of 

 the Rochelle Salt Method. Thus a strip of metal film '78 cm. 

 long and 1 cm. wide was left exposed. Fine copper wire 

 was wound around these edges and electroplated, by means 

 of a copper deposit, to the silver below — thus furnishing a 

 good connexion between the copper wire and the film of 



