468 Prof. McLennan and Mr. Ireton on Fundamental 



Paet II. 

 1. Introduction. 



In a paper by McLennan and Thomson on Bunsen Flame 

 Spectra some experiments are described which were designed 

 to throw light on the question of which of the two series 

 v=(l'5, S) — (m, p 2 ) and i/=(l'5, S) — (in, P) was the more 

 fundamental from the point of view of vibrations within 

 the atom. A Bunsen flame was chosen as being perhaps 

 the most simple method of stimulating atoms to the emission 

 of radiation, and the vapours of pure metals rather than 

 those of their salts were used with a view to realizing the 

 simplest possible conditions within the flame from a chemical 

 point of view. 



With mercury vapour the monochromatic radiation of 

 wave-length X = 253672 A.U., v=(l"5, S)— (2, p 2 ) was ob- 

 tained, but no trace of the line at \ = 1849'6A.IL, v = (l"5, S) 

 — -(2, P) appeared, even when the Bunsen flame was strongly 

 forced. With cadmium vapour the line at X — 32 GO* 17 A. U., 

 v=(l'5, S) — (2, p 2 ) came out when the flame was burning 

 gently, and the line at X = 2288*79 A.U., i/ = (l'5, S)— (2, P) 

 as well when the flame was O forced. With magnesium 

 vapour the line at X = 2852-22A.U., v=(l'5, Sj— (2, P) 

 was obtained, but no trace of the line at \ = 4571A.U,, 

 v=(l*5, S) — (2, p 2 ) appeared on the plates unless the 

 many-lined spectrum appeared. With zinc no photographs 

 belonging to the spectrum of the metal were obtained unless 

 the metal was very strongly heated so that a copious 

 supply of vapour was sent into the flame. Under these 

 latter circumstances oxidation was intense and the vapour 

 frequently took fire. The spectrum of zinc which was then 

 obtained consisted of a large number of lines of greater or 

 less intensity. From these results it will be seen that while 

 the importance of the two series v = (l*5, S) — (2, p 2 ) and 

 v= (1*5, S) — (m, P) was emphasized, tbere was little evidenee 

 brought forward as to which of the two series was the more 

 fundamental. 



Ramage * in his admirable paper on " Relations of Spectra, 

 etc., to Atomic Mass," was the first to identify the line 

 X — 3075*99A.U .in the flame spectrum of zinc. It appears, 

 he pointed out, among the series of lines constituting the 

 strongest water-vapour group. Our attention has also been 



* Ramage, Proc. Roj.Soc. No. 459, vol. Ixy. p. 1 (1901). 



