

and their Magneto-optic Properties. 211 



6. Destruction of Fluorescence by Magnetic Field. 



I have taken the liberty of copying the title of this section, 

 literally, from Wood and Ribaud's paper already quoted *, 

 first, because it is a short title and, second, in order to better 

 recall the reader's attention to that experimental paper. It 

 will be well to quote also a few lines from Wood and Ribaud's 

 paper. On p. 1017 the authors say : — 



" Under these conditions we estimated the reduction of 

 " intensity [of iodine vapour fluorescence] to amount to f idly 

 " 90 per cent, with afield of 30,000 gauss, and it is probable 

 " that with a field of 50,000 the fluorescence would be 

 " practically destroyed. . . . No obvious explanation of the 

 " effect of the field in reducing the intensity of and ultimately 

 "practically destroying the fluorescence suggests itself" t- 



Now, such a dependence of intensity of fluorescence upon 

 the magnetic field has already been hinted at, just after the 

 equations (14). We shall now see that these equations not 

 only account for the observed effect, but, bringing it into 

 close connexion with the magnetic rotation f (and £ 

 especially), make the explanation so plain that it can be 

 seen almost immediately. In fact, let I be the intensity of 

 any line (taken separately), when the vapour is placed in a 

 field H. Then, disregarding ellipticity, 



2I=|A| 2 + |B| 2 , 



where A, B are given by (14). It will be enough to consider 

 here, in detail, the fundamental line only. Writing, in (14) ? 

 n = N, we have 



[A| = S. *±L [B| = S k ~ Z 



N P-f-Z 2 ' ' ' N " F + Z 2 ' 

 whence, for any H, 



i= ^ 



N 2 (P + Z 2 )' 



and, therefore, for H = 0, I = c 2 /Wk 2 . Thus, the ratio of 

 the two intensities, J = I(H) : I(o>> 



Jo= T+(W (23) 



where the suffix is to remind us that the fundamental line 

 is concerned. Thus, with increasing intensity of the magnetic 

 field the fundamental fluorescence tends to nothing. 



* " Destruction " stands, of course, in general, for " diminution of 

 intensity." 



f The few words are italicized by the present author. 



