Electronic Frequency and Atomic Number 

 Table I. 



489 



Element. 



N.. 



X in ftp. 



vXlO" 14 . 



N^xlO -15 . 



Li 



3 

 11 



19 

 37 



280 

 340 

 435 

 480 



10-71 



8-82 

 6-90 

 6-25 



1x3-21 

 3x3-23 5 

 4x3-27.5 

 7x3-30 



Na 



K 



Rb 



The figures in the last column of the table show that Nv 

 may be expressed in the form nv E , where n is a simple 

 integer and v E is very nearly constant. The mean value 

 of i/ B for these four elements is 3*255 x 10 15 sec. -1 , which is 

 so near the Rydberg value 3*289 x 10 15 sec. -1 that there can 

 be no reasonable doubt as to the identity of the two 

 numbers. 



Pohl and Pringsheim also record a maximum photo- 

 electric activity in the case of the four metals magnesium, 

 aluminium, calcium, and barium; but they do not regard 

 these elements as showing a true " selective " effect in the 

 sense in which they use that expression. Sometimes the 

 maximum is not observed till some time after the first pre- 

 paration of the metal surface, Provided, however, the 

 maximum is in some sense characteristic of the metal in 

 question, we might expect to find that the corresponding 

 frequency is related to the atomic number in a way similar to 

 that already found for the alkali metals. That this expecta- 

 tion is realized, at least approximately, is shown in Table II., 



Table II. 



Element. 



N. 



X in juju. 



i^XlO" 14 . NvXlO- 10 . 





Mg 



Al 



12 

 13 



20 

 55 

 56 



250 

 254 



220 

 350 

 250 

 280 



120 



11-8 

 13-6 

 8-57 

 120 

 10-7 



4* x 3-20 



5x3-07 



5x354 



5x3-43 



20x3 30 



18x3-33 



1. 



1. 

 2. 



1. 

 2. 



1*. 



Ca 



Cs 



Ba 



1. Pohl and Pringsheim. 2. Richardson and Compton. 



which also includes results obtained by Richardson and 

 Compton *. The values of v E in this Table do not show the 



* Bichardson and Compton, Phil. Mag. vol. xxiv. p. 575 (1912), 

 vol. xxvi. p. 549 (1913). 



