THE 

 LONDON, EDINBURGH, and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[SIXTH SERIES.] 



SEP v ° l 



SEPTEMBER 1916. 



*£PATENJ Q 



XXXII. On Fluorescent Vapours and their Magneto-optic 

 Properties. By L. Silberstein, Ph.D., Scientific Adviser 

 to Adam Hilger, Ltd.* 



1. General Remarks. 



THE fluorescence of vapours, such as iodine vapour, 

 excited by light of a particular, appropriately chosen, 

 frequency N, gives what Wood calls a resonance spectrum, 

 consisting of a series of lines, whose frequencies are n = N 

 and, say, n l5 n 2 , n 3 , etc., where the latter stand in some 

 relation to the fundamental frequency N. 



Now, an ordinary oscillator or resonator, of free period 

 T = 27r/N and relaxation- or extinction-time t = 2/&, i. e. a 

 system obeying the familiar differential equation 



^+&i? + N 2 <2? = 0, (H) 



when acted upon by an external force of frequency n, gives 

 only oscillations of the same frequency n, and of no other in 

 addition. (And, assuming T/t small, the resonator answers 

 vigorously only when n=N.) Since this simple behaviour 

 is due to the assumption of Hooke's law for the restitutive 

 elastic force, i. e. force proportional to displacement x, we 

 can appropriately call a system obeying the equation (H) a 

 Hookean resonator. On the other hand, if N 2 <r is replaced 

 by a non-linear function of #, an exciting force of frequency 

 N will generate oscillations of frequency N and also an 

 infinite variety of other frequencies. 



* Communicated by the Author. 

 Phil. Mag. S. 6. Vol. 32. No. 189. Sept. 1916. T 



