﻿521- Fluorescence and Magnetic Spectra of Sodium Vapour. 



As will be seen by reference to the chart, the first series 

 has the largest average spacing, and the fifth the smallest, 

 the u scale," if the term is allowed, decreasing gradually from 

 the first to the fifth, the two coming into coincidence at about 

 wave-length 4860. 



Doubtless these series could be extended to wave-length 

 5500 or thereabouts by making use of the grating-photograph 

 of the complex fluorescence obtained by white-light stimulation. 

 The lines are, however, so diffuse in their nature, with over- 

 lapping wings and other peculiarities, that I have not yet 

 attempted any further extension. I think that by employing 

 a much denser vapour the magnetic spectrum can be consi- 

 derably extended ; and as the lines are much .sharper in this 

 case, an extension of the series will be an easy matter. The 

 other series necessary to give the close spacing found in the 

 yellow may be discovered in this manner. 



A theoretical discussion of the results will have to be 

 deferred to a subsequent paper. In fact, I prefer to have 

 this side of the subject attacked by those who have given 

 especial attention to the theory of molecular radiation. The 

 absence of many lines in each series in the magnetic spectrum, 

 and the absence of certain lines in the fluorescent spectrum, 

 are especially suggestive. We have similar conditions in 

 other series of lines, as is well known ; but the present case 

 is, so far as I know, the only one in which we can, by varying 

 the exciting conditions, bring about a change in the position 

 of the absent lines. It appears to me that the data furnished 

 us by sodium vapour ought in the end to enable us to 

 choose between the various theories proposed to account for 

 spectrum series. 



The investigations recorded in the present paper have 

 been made possible through generous aid given from the 

 Rumford Fund by the American Academy of Arts and 

 Sciences. 



I feel also under .great obligation to my assistant Mr.ftF. 

 W. Cooper for the many hours of very fatiguing work which 

 he devoted to the research. 



