578 Prof. 0. W. Richardson and Mr. K. T. Compton on 



metal readings were taken for wave-lengths 25/23, and 21. 

 The unit of wave-length is 10~ 6 cm. The readings are 

 shown in Table I. V is the externally applied potential 

 difference, R is the deflexion in scale-divisions per minute, 

 and C is this deflexion reduced to a scale of 100 for the 

 maximum deflexion. These readings may be taken as typical 

 of all the distribution of velocity curves that we have 

 obtained. 



It i* necessary to correct these readings for contact differ- 

 ence of potential. The method of determining this correction 

 will be described later. After being thus corrected the 

 numbers in Table I. are plotted thus: — o in fig. 2 (PI. XIII.). 

 The significance of these curves may be explained as 

 follows : — Take, for instance, the curve for 23 \. The 

 ordinate at — 0'5 volt is 44. This means that 44 per cent, 

 of the electrons are liberated with velocities equal to or 

 greater than that velocity which gives them sufficient energy 

 to overcome an opposing difference of potential of 0"5 volt. 



Table I. 





X = 25. 



X=23. 



X=21. 



V. 



4- 2 



E. C. 



41 98 



42 100 



41 98 



42 100 

 42 100 

 42 100 

 40 95 

 27 64 



9 22 

 3 7 

 



R. C. 



78 100 

 78 100 

 78 100 

 78 100 

 78 100 



76 97 



68 87 



54 69 



44 56-5 



30-5 39 



19 24 



8 10 



1-5 2 







R. C. 



31 100 

 31 100 

 31 100 

 31 100 

 31 100 



30-5 98-5 

 29 93 

 26 84 



21 68 



15 48 



8'5 27 

 65 19 

 3 10 



1 



0-5 



0-2 



01 



0-05 



00 



_o-i 



02 ......... 



0-3 



0-4 



0-5 



0-6 



0-7 



0-8 



0-9 



1-0 







To obtain the relative number which are emitted with any 

 given energy, we must differentiate these curves with respect 

 to V. The result of this differentiation is shown in fig. 3. 

 For wave-length 25 the number emitted with an energy 

 corresponding to 0*2 volt is to the number corresponding to 

 0*1 volt as the ordinate in fig. 3 at 0*2 volt is to the ordinate 

 at # 1 volt, or as 00 is to 65, and so on. 



