696 On the X-ray Spectra of the Elements. 



Table I. (K series.) 



t'Xicr 8 * 



Element. N. \Xl0 8 . i-xlO -8 . 2(N-2). (determined 



experimentally). 

 W 74 0-210 145 144 — 



Nd 60 0-333 115 116 — 



Sn 50 0-489 95-1 96 



Zr 40 0791 750 76 — 



Se 34 1-107 634 64 738 



Zn 30 1-435 55-6 56 63'2 



Or 24 2-286 44-0 44 509 



Ca 20 3-357 36-3 36 



Na .11 11-951 18-5 18 



It will be seen from columns 4 and 5 that r= 2(N — 2)10 8 

 cm./sec. for these calculated A T alues of v. 



Column 6 gives the values of v determined experimentally 

 for selenium, zinc, and chromium f . It appears that the 

 experimental values of v in these three cases are about 16 per 

 cent, greater than the calculated values — a result in general 

 agreement with Webster's J more recent experiments. 



Table II. is a repeat of Table I. for the L series from U 

 to As, the 6th column being omitted owing to lack of data. 



Table II. (L series.) 



Element. N. XxlG 8 . t-XlO" 8 . (N-15). 



TJ 92 . 0-720 78-4 77 



Hg 80 i-049 65-0 65 



Yb 70 1-474 54-9 55 



Nd 60 2-167 45-3 45 



Sn 50 3-381 36'2 35 



Zn 40 5-851 27-5 25 



As 33 9-449 20-7 18 



It will be seen from a comparison of columns 4 and 5 that 

 for the L series v=(N— 15) 10 8 cm./sec. very approximately. 

 The agreement is not nearly so close as for the K series. 



Summary. 



The speed of electron (v) carrying the same energy as the 



u lines in the K and L spectra of the elements is shown to 



be fairly well represented by the formula a==O.N + D 5 



where N is the atomic number of the element, and C and D 



are constants determined by the series. 



For the K series f)/AT n ., a r - 



v — 2{N —2) 10 s cm./sec, 



and for the L series 



v s= (N — 15) 10 8 cm./sec. 



* See Kaye's ' X-Rays,' p. 133, 3rd edition (1918). 

 t Whiddington, Proc. Roy. Soc. 1911. 



X Webster, Phys. Rev. 1916, vol. vii. p. 612. It appears that this 

 16 per cent, represents the difference between the a and y components. 



