2 Mr. H. Ramage. Relations of Spectra, Densities, [Nov. 7, 



Lecoq de Boisbaudran,* in proposing a theory on the origin of the 

 spectral lines, made the following observations : — 



" Les raies spectrales des metaux alcalins (et alcalinoterreux), 

 classes par leur ref rangibilites, sont placees, comme les proprietes chimi- 

 ques, suivant l'ordre des poids atomiques." 



"Le spectre du rubidium parait done alors analogue a celui du 

 potassium, etant seulement transported comme tout d'une piece, vers le 

 rouge." 



Boisbaudran later (1870) laid stress upon these analogies, especially 

 between the spectra of potassium, rubidium and caesium, but he made 

 no reference to the spectra of lithium and sodium. 



In 1886f he extended his comparative researches on spectra, and 

 calculated the atomic weights of gallium and germanium from data 

 supplied by their spectra and the atomic weights and spectra of other 

 elements. Ames criticised this work, J and showed that the method 

 failed when applied to other elements. 



The discovery of harmonic series of lines in the spectra of elements 

 by Liveing and Dewar,§ and the work of Hartley|| on "Homologous 

 spectra," indicated that there was a general law which applied to the 

 production of the spectra of several elements. The formulae which 

 have been applied to these series, notably by Balmer, Kayser and 

 Runge, and, more especially, the formula and work of Ryclberg, have 

 emphasised this fact in a most striking manner. Rydberg"[f discussed 

 the spectra of the more common monad, dyad and triad metals very 

 fully, and enunciated several important laws. His work will be con- 

 sidered in some detail in the course of this paper. 



Methods available for the Selection of the Corresponding Lines in Spectra. 



Ames, in discussing the difficulty of discovering these lines,** said 

 that the first really scientific work in this direction was done by 

 Hartley's discovery of the constant differences of oscillation frequency 

 between the members of doublets and triplets. ft 



Liveing and Dewar's harmonic series of lines, and the formulae of 

 Rydberg and of Kayser and Runge, give valuable assistance in this 

 part of the work. 



The author was led to begin this investigation by the knowledge of 

 flame spectra which he acquired whilst working with Professor Hartley. 



* ' Comptes Eendus,' vol. 69, 1869. 



f Ibid., vol. 102, pp. 1291-5. 



X ' Phil. Mag.,' 5th series, vol. 30, p. 47, 1890. 



§ < Phil. Trans.,' vol. 174, pp. 187-222, 1883. 



|| ' Trans. Chem. Soc.,' vol. 43, p. 390, 1883. 



f ' Kongl. Svenska Yetensk. Akad. Handl.,' vol. 23, Ko. 11, 1890. 

 ** ' Phil. Mag.,' vol. 30, 1890, p. 47. 

 ft ' Trans. Chem. Soc.,' vol. 43, p. 390-400. 



