FLUORESCENCE AND MAGNETIC ROTATION SPECTRA OF 

 SODIUM VAPOR, AND THEIR ANALYSIS. 



By R. W. Wood. 



Presented by C. R. Cross. Received August 7, 1906. 



Previous work, which has been recorded in the Philosophical Maga- 

 zine,^ convinced me that a careful study of the remarkable optical 

 properties of the vapor of metallic sodium would, in time, furnish the 

 key to the problem of molecular vibration and radiation. This opinion 

 has been strengthened by the work of the past year, and though much 

 remains to be done, it seems best to place the results already obtained 

 on record. In no other case that I know of is the molecular mechan- 

 ism so completely under the control of the operator. Its periodicities 

 can be studied in a variety of ways : by absorption, by cathode-ray 

 stimulation, by excitation with light, either white or monochromatic, 

 and lastly by its remarkable selective magnetic rotation of the plane 

 of polarization. 



The vapor is, in every case, that obtained by heating metallic sodium 

 in steel or porcelain tubes, usually highly exhausted. From a study 

 of the dispersion of the vapor, it seems probable that we may be deal- 

 ing with clusters of molecules with which a certain amount of hydro- 

 gen may be associated. 



As I have shown in a previous paper,^ if a pool of sodium is heated 

 in a highly exhausted horizontal tube, the top of which is cooler than 

 the bottom, the vapor has an enormous optical density close to the 

 surface of the pool, and a very small density along the roof, the non- 

 homogeneous layer acting as a prism. The only way in which I can 

 reconcile this state of things with the kinetic theory is to assume that 

 the vapor leaves the metal in the state of molecular clusters, which 

 gradually break up into smaller clusters and eventually into molecules. 

 This is of course only an hypothesis, and I mention it in the present 

 paper merely to indicate that our vibrating mechanism may be an 



1 Magneto-optics of Sodium Vapor, Phil. Mag., Oct., 1905. The Fluorescence 

 of Sodium Vapor, Phil. Mag., Nov., 1905. 



2 A Quantitative Determination of the Dispersion of Sodium Vapor, These 

 Proceedings, 40, 335. 



