between Spectra and Atomic Weights. 207 



And the convergence-frequencies 31502, 337 62. and 35086 

 give 86*0*2 . 



Mitscherlich, so long ago as 1864, pointed out the similarity 

 in the spectra o£ the chloride, bromide, and iodide of barium, 

 and endeavoured to trace a connexion with the atomic weights 

 of these compounds. 



Lecoq de Boisbaudran in 1869 called attention to the 

 spectra of the metals of the alkalies and alkaline earths, re- 

 marking that the spectrum of caesium is like that of potassium 

 shifted bodily towards the red. Hartley in 1890 showed that 

 three triplets in zinc corresponded with three triplets in 

 cadmium, and that in each of these spectra the triplets had 

 their lines similarly spaced if mapped on the scale of oscil- 

 lation-frequency. Kayser and Runge in 1891 confirmed this 

 statement, and point out many more triplets similarly related, 

 for which they found a connecting formula of the form 



I =A{l-Bn- 2 -Cn-+). 



They further call attention to the fact that the differences in 

 oscillation-frequency in the triplets increase with increase of 

 atomic weight; and that they are nearly as the squares of the 

 atomic weights. They also remark that in the spectra of 

 potassium, rubidium, and caesium the mean differences of the 

 close pairs are nearly proportional to the squares of the atomic 

 weights. 



Eamage (Proc. Roy. Soc. 1901) has discussed many of 

 these relationships, and gives two diagrams with oscillation- 

 frequencies as abscissae, one with atomic weights as ordinate-, 

 the other with the squares of atomic weights as ordinates. 

 He points out that in the second of these two diagrams, the 

 lines connecting corresponding points are nearly straight in 

 the case of potassium, rubidium, and caesium ; and in the 

 case of calcium, strontium, and barium. He remarks also 

 that "curious results were obtained by observing the points 

 in which the converoino- lines, drawn through corresponding 



to jp ' to l .— > 



members of doublets and triplets, intersected. It was difficult 

 to determine these points accurately, and the results have 

 since been regarded more as coincidences."" 



In a more recent paper (June 5th, 1902) on the spectra of 

 potassium, rubidium, and caesium Ramage confirm- his 

 previous results, and says that the lines connecting corre- 

 sponding members of homologous doublets do actually intersect 

 on the line of zero atomic weight. 



