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curves for the spectral response of various states obtained by oxidation 

 followed by diffusion at room temperature and at 75° C, and then 

 include curves for the spectral response of various states obtained by 

 the slow deposition of caesium we may obtain a composite family of 

 curves such as are sketched in Fig. 20 to show the whole sequence 

 of response characteristics whose parameter is the thickness of the 

 surface film of free casium. In obtaining curves for this composite 

 progression of states we have not considered surfaces after they were 



6000 



7000 



8000 

 WAVELENGTH IN A 



9000 



10000 



Fig. 20 — Relative spectral response to equal energy of a csesium-oxygen-silver cell 

 as an idealized function of film thickness. 



baked at 200° C. because of the likelihood at this temperature of 

 surface changes other than in caesium concentration alone. 



When the amount of c£esium in the surface is far below the normal 

 (as after admitting oxygen equivalent to six layers of caesium) we have 

 a spectral response which decreases continuously with increasing 

 wave-length, as shown in curve 1 of Fig. 20, This is the same type 

 of response as obtained by Roller ^ from cells prepared by treating 

 with caesium a silvered bulb with an adsorbed film of oxygen which 

 gave a type of surface designated by him as "Cs-O-Ag." With 

 increasing film thickness the response increases at all wave-lengths 



^ Loc. cit. 



