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XXIX. The Dependence of the Intensity of the Fluorescence 

 of Dyes upon the Wave-Length of the Exciting Light. By 

 S. I. Vavilov, Lecturer in Physics at the University of 

 Moscow *. 



THE connexion between the energy of exciting light and 

 the intensity of fluorescence can be expressed on the 

 ground of a precisely established experimental law t as 



j; 



i-i / -=F = «.I A .a A .AX, . . . . " (1) 



y A f 



where /a/ is the energy of fluorescence corresponding to the 

 interval of wave-lengths of fluorescence d\f, F the integral 

 energy of fluorescence, 1^ energy of exciting light, «\ the 

 part of the light absorbed by the fluorescent dye in a finite 

 small interval AX. The coefficient 



gives the energy of fluorescence per unit of absorbed energy; 

 we shall call it " specific fluorescence." The value of k is 

 generally a complicated function of X. The first stage of 

 the problem which arises here is the dependence of k upon 

 X within an isolated absorption-band. An attempt at an 

 experimental solution of this problem was made by Nichols 

 and Merritt f . These authors found that the specific fluores- 

 cence of Eosin and Resorufin increases towards long wave- 

 lengths, for Resorufin by 2*7 times (at the change of 

 wave-length of exciting light from 520 /mp to 600 yLtyw.) and 

 by 1*63 times for Eosin (480 pp to 560 pp). The authors 

 have stated a generalization of these results § without giving 

 a theoretical explanation. 



We suppose that the question of the dependence of k upon 

 wave-length inside an isolated absorption-band is closely 

 related to the problem of the nature of these bands in liquid 

 and solid bodies, and has equally considerable significance 

 for the theory of dispersion and absorption as well as for 

 its bearing upon the theory of fluorescence. 



The fundamental law (L) shows the secondary character 

 of fluorescence, which is regulated by the value of the 

 energy accumulated in the given molecular resonator. In 



* Communicated by the Author. 



t Cf. J. Hattwich, Wiener Ber. Bd. 122. Abt. 11 a (November 1913). 

 t E. L. Nichols and E. Merritt, Phvs. Rev. I. xxxi. pp. 376, 381 (1910). 

 § E. Merritt, Phys. Rev. II. v. p. 328 (1915). 



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