734 Prof. W. M. Hicks on the 



twice the heat evolved in the half-period. Therefore 

 ' 1-532 Xl0 7 



Q = 2f (2-98xl0 4 )6-( 4 - 52 >< 10 ~^^ 



_ f 2-98 xlO 4 r -4-52xio- 8 ni-532 X ion 

 - 2 \__4'52xlO- 8 L J J 



= 6*G XlO 11 cal. 



= 2-76 XlO 19 ergs. 



Then 



AM- 2 ' 76 * 10 19 

 ■ 9-00xl0 20 



= 0-0307 gm. 



The entire change of mass between radinm and lead cannot 

 be very mnch larger than this, since the only changes 

 between these two elements which are not included in the 

 thermal data are those between radium C and lead. 



May 29, 1915. 



LXXVII. Note on the Calculation of Series in Spectra. 

 By W. M. Hicks, F.R.S* 



IN the October number of this Journal appears a joint 

 paper by Mr. Savidge and Prof. Nicholson on the 

 calculation of series in spectra, occasioned by a supposed 

 difficulty in testing for series, and in calculating the formula 

 constants. As a fact, however, the usual method of testing 

 for series by the aid of Bydberg's table is quite simple. 

 The determination of the formulaa constants requires natur- 

 ally a certain amount of numerical work. Possibly an 

 explanation of the method I have adopted in my own 

 work may be of interest to others. I find it takes about 

 twenty minutes' work — including verification — to obtain all 

 the constants involved. 



As an instance of test the complete set of OD/" may be 

 taken, the 2nd, 3rd, and 4th of which were used as examples 

 by the authors. The wave numbers referred to vacuo are 

 given in the first of the following columns : — 



* Communicated bv the Author. 



