40 Mr. J. S. Ames on Relations between 



tional lines ; but M. Julius gives equal importance to each 

 line, faint or strong, hazy or sharp. The spectrum of calcium 

 has some very strong lines in the red ; and, as their wave- 

 lengths have recently been carefully determined by Prof. 

 Rowland, I thought I would test this theory by means of 

 them. My search was in vain : not a combinational line 

 could I find. 



Distribution of Lines. 



For many years spectroscopists have sought to reduce the 

 distribution of lines in any one spectrum to a mathematical 

 formula, but without much success. There are, however, one 

 or two brilliant exceptions. 



In 1885 J. J. Balmer* gave a formula for the lines in the 

 hydrogen spectrum, which is most simple and which, as will 

 be seen later, is remarkably accurate. His formula is 



m s — 4 ; 



where \ is a constant and m takes in succession the values 

 3, 4, 5 ... . More will be said of this formula when the hy- 

 drogen spectrum itself is discussed. 



A formula was also advanced by Nordenskiold f , the Arctic 

 explorer ; but it is quite inaccurate. 



These two formulae were found by trial ; but it is interest- 

 ing to note that one similar to Balmer' s has been deduced 

 theoretically. A general theory of radiation has been devised 

 by Herr Kovesligethy J, and in the course of this he arrives at 

 the following wave-length formula : — 



E-l 



where jjl is the value of fi for the temperature of dissociation, 

 fju being a function of the temperature and constitution of the 

 body ; and R is a function containing a parameter which 

 must be determined for each substance. This formula is most 

 suggestive ; and the appearance of the elaborate treatise on 

 the general theory, which is promised us, is eagerly expected. 

 In their first contribution to the " Spectra of the Ele- 

 ments " § Kayser and Runge announce that they have found 

 a general law for all spectra, which includes Banner's as a 

 special case. The uncertainty of the measurements of the 



* Wied. Ann. xxv. (1885). 



t Comptes Rendus, cv. (1887). 



% Astr. Nachr. p. 2805 (1887) ; Beibl. xii. pp. 346 and 579 (1888). 



§ Abhd, Berlin Acad. 1888. 



