[ 536 ] 



LXVI. On Unsymmetrical Broadeniiu/ of Spectral Lines. By 

 George W. Walker, M.A., A.R.C.Sc, Fellow of Trinity 

 College, Cambridge *. 



A PERUSAL o£ chapters 5 and 6, vol. ii. of Kavser's 

 ' Handhucli der Spectroscopie ' readily convinces one 

 that the conditions which determine the broadening of a 

 spectral line are extrem€'Jy complex, and that comparatively 

 little progress has been made towards the disentanglement o£ 

 the various factors which determine the appearance of a 

 line. 



Nevertheless, some general features appear to have been 

 established beyond doubt. One of the most important of 

 these is that when a line is broadened, by whatever means, 

 the broadening is in general unsymmetrical. 



The vast majority of lines show a broadening towards the 

 red end of the spectrum ; but there are cases in which there 

 is no measurable effect, and some in which the broadening 

 is distinctly towards the violet. 



The theories which have been proposed explain broadening 

 towards the red, but are unable to explain a broadening 

 towards the violet. The Doppler Theory applied to moving 

 molecules leads to the result that the breadth of the line 

 should be proportional to the wave-length. But although in 

 general the breadth is found to be greater for greater wave- 

 lengths, the law is by no means so simple as that just 

 mentioned. Again, Godfrey f has shown that owing to a 

 numerical error in Michelson's work J, the Doppler Theory 

 is not sufficient to account for the whole breadth^ but only 

 for about one half of it. 



My object in this paper is to show that unsymmetrical 

 broadening may be accounted for in a manner quite different 

 from any theories that have been hitherto proposed, and that 

 the effect may in some measure contribute to an explanation 

 of the observed facts. 



Whether the luminous radiations are produced in a flame 

 at high temperatures, or by the electric discharge in any 

 form, there can be no doubt of the presence of free 

 negatively-charged particles (corpuscles) in the immediate 

 vicinity of the source from which the radiations proceed. 

 I propose to show that these negative particles modify the 

 light which they receive and again scatter, in a manner 



* Commauicated by the Author, 

 t Phil. Trans, vol. cxcv. p. 329. 

 t Phil. 31ag. vols. xxxi. & xxxiy. 



