204 



J. IStanley Rogers: 



Siegbahn's and Duane and Stenstrom's values were assumed. 

 These are as follow : — 



\/or Wa2=-21347 x lO-«cm 



Wa,=-20873 „ „ 



W/3 = -18428 „ „ 



The value in Angstrom units per mm. of the projection was 

 found from the mean of the distances between the Wa^ and 

 "W/S lines, and the Wai and Wj8 lines. The wave lengths of the 

 other lines were then calculated proportionally. As a test of 

 the accuracy of the method, the value of the wave length of 

 the Wy line was obtained. The mean value is given below. 

 The mean of the values obtained for this line by the above 

 authors is .17921.A.U. 



The method employed rests on the assumption that the wave 

 lengths of the lines on the film are proportional to the angles at 

 which they are reflected at the crystal. According to Bragg's 

 formula, X=:2d sin 0, these wave lengths are proportional to the 

 sine of the angle. No error was introduced in the values given, 

 below since 6 for Ka2=:2°(^./.) and 6 for Pt.y=l°30'(^./.) 



Results and Discussion. 



In Table II. are given the values obtained. The wave lengths 

 were calculated to five decimal places, and the final values are- 

 given to four places, with the probable error. 



Table II. (\ in Angstrom Units). 

 Wave Lengths of K Series of Platinum. 



Film No. 



Pt-a^. 



Pt.«i. 



Pt./3. 



Pt.y. 



Wy. 



P.14 

 P.15 

 P.16 



•18939 

 •18926 

 •18998 



•18496 

 •18536 

 •18502 



•16455 

 •16427 

 •16429 



•15955 

 •16968 

 •15942 



•17952 

 •17905 

 •17973 



Mean - 



•18954 



18511 



•16437 



•15955 

 •1596±2 



•17943 



Final - 



•1895^2 



•1851±1 



•1644±2 



•1794±2 



Lilienfeld 

 and Seeman 



•1907 



•1853 



•1642 



•1593 



— 



In the last line of the table the values obtained by Lilienfeld 

 and Seeman are inserted for comparison. The agreement is good 



