524 Prof. R. W. Wood on Separation of Close 



stationary states is governed by the ordinary laws or! me- 

 chanics, while these laws do not hold for the passing of the 

 system between the different stationary states. 



3. That the radiation emitted during the passing of the 

 system between two stationary states is homogeneous; and 

 that only in the region of slow vibrations does the frequency 

 approach that to be expected on ordinary electrodynamics, 

 while in general the frequency v is determined by the relation 

 E = h . v, where E is the total amount of energy emitted 

 and h Planck's constant. 



It has b3en attempted to show that, applying these assump- 

 tions to Rutherford's theory of the structure of atoms, it seems 

 possible to obtain an explanation of the laws of line-spectra 

 discovered by Balmer, Rydberg, and Ritz. 



It has further been attempted to show that it seems possible 

 to account for some of the general features of the effect of 

 magnetic and electric fields on spectral lines discovered by 

 Zeeman and Stark. In the case of an electric field it is 

 assumed that no alterations in the above assumptions take 

 place. In the case of a magnetic field, however, it is found 

 necessary to modify the third assumption in order to retain 

 the connexion with ordinary electrodynamics in the region of 

 slow vibrations. 



LX. Separation of Close' Spectrum Lines for Monochromatic 

 Illumination. By R. W. TVoOB, Professor of Experimental 

 Physics, Johns Hopkins University, and Adams Research 

 Fellow of Columbia University*. 



[Plate VII.] 



IN many branches of research in physical optics it often 

 becomes necessary, for one reason or another, to separate 

 two or more close spectrum lines, utilizing the light of one 

 only. 



For example, in experiments upon the monochromatic 

 excitation of resonance spectra, the line utilized for the 

 illumination of the fluorescing vapour must be isolated 

 either by absorbing screens or by a spectroscope, used as a 

 monochromator. 



If the latter method is employed the illumination is'much 

 restricted by the necessity of employing a slit, or rather two 

 slits; and in the case of close spectrum lines, such as the D 

 lines of sodium, the necessity of employing very fine slits 

 makes it very nearly impossible to accomplish anything in 



* Communicated by the Author, 



