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XC. On Quetelet's Rings and other Allied Phenomena. By 

 C. V. Raman, M.A., Palit Professor of Physics, and 

 Goverdhan Lal Datta, M.A., Palit Research Scholar, 

 University of Calcutta *. 



[Plate XXV.] 



Contents. 



1. Introduction. 



2. Observations of Quetelet's Rings at Oblique Incidences. 



3. Configuration of the Rings. 



4. Quetelet's Rings by Multiple Reflexion. 



5. Quetelet's Rings in Crystalline Plates. 



6. Influence of Structure of the Scattering Film. 



7. Theory of the Phenomena. 



8. Summary. 



1. Introduction, 



WHEN a distant point-source of light is viewed by 

 reflexion from a plane mirror silvered on the 

 back, the scattered light surrounding the reflected image of 

 the source exhibits a system of coloured rings, the brilliancy 

 of which is greatly enhanced by purposely dimming the 

 front surface of the mirror, as, for instance, by breathing 

 upon it. These rings (generally referred to in the literature 

 as Quetelet's Rings) belong to the same class of diffraction 

 phenomena as the well-known " diffusion " rings surrounding 

 the focus of a thick concave mirror discovered by Newton. 

 The generally accepted theory of their formation was put 

 forward originally by Stokes f and was subsequently elabor- 

 ated by Lommel % and Exner§. It is proposed in this 

 paper to draw attention to several novel features which the 

 authors have observed in the course of an experimental study 

 of the phenomena under various conditions. In considering 

 the explanation of these features, it will be shown also that 

 the hitherto accepted theory of Quetelet's rings and other 

 related phenomena requires revision in certain respects. 



* Communicated by the Authors. 



t Mathematical and Physical Papers, vol. iii. pp. 155-196. 

 % Annalen der Physik, vol. viii. p. 193 (1879). 



§ Sitzungsberichte of the Vienna Academy, xc. p. 827 (1884), and Ann. 

 d. Physik, vol. ix. p. 239 (1880). 



