358 



BELL SYSTEM TECHNICAL JOURNAL 



cells are presented in which rates of deposition of free caesium differing 

 by a factor of 700 were obtained. The sizes of the orifices differed 

 and positions on each cathode at different distances from the orifice 

 were observed. Measurements of spectral response were made with 

 the light incident upon each of the four positions on the cathode 

 shown in Fig. 7. 



From simple kinetic considerations we may derive a formula for 



tr 200 



7000 



6000 

 WAVELENGTH IN A 



9000 



Fig. 12 — Relative spectral response to equal energy for cell C, position 1. 



the rate of deposition upon a surface of the vapor effusing from the 

 orifice : 



W = 0.01857VM/r^%^cos d cos ^, 



where W is the weight deposited per cm.^ per second (in grams), 

 M is the molecular weight of the vapor, a is the area of the orifice, 

 ^mm. is the pressure within the cylinder in millimeters of mercury 

 (i.e. the vapor pressure of caesium ^^), r is the distance from the orifice 

 to the surface, 6 is the angle between r and the normal to the plane 

 " Int. Crit. Tables III, 205. 



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