THE 



LONDON, EDINBURGH, and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



SUPPLEMENT to VOL. L. FOURTH SERIES. 



LIX. On the Polarization of the Light of the Sky. 

 By R. H. M. Bosanquet, Fellow of St. John's College, Oxford*. 



rj^HE subject of the polarization of the light of the sky has 

 J- been regarded from two principal points of view — namely, 

 as matter of observation, and as the subject of a theory based on 

 TyndalPsexperiments with attenuated vapours and smoke. The 

 comparison of the observations of the sky with the experiments 

 has not yet been carried out to any purpose, so far as I am aware. 

 It will be the aim of the present communication to discuss the 

 results of observation of the sky in the light of certain elemen- 

 tary indications afforded by the experimental treatment. A 

 few words will be said on the general theory. The subject of 

 the construction of polarimeters will also be noticed, and some 

 remarks made on the principles on which the interpretation of 

 their indications may be made to depend. 



By far the most complete treatment of the matter by obser- 

 vation of the sky is that of Brewster. His map of the lines of 

 equal polarization was published in Keith Johnston's ' Physical 

 Atlas/ accompanied by a short explanation. It has never, so 

 far as I know, been unfavourably criticised, and is the authority 

 to which probably any one interested in the subject would look 

 in the first instance. On inspecting this map it appeared to me 

 so strange, that I thought it desirable to investigate the matter 

 more closely; and I have now to present the considerations 

 which lead me to the conclusion that it must be almost entirely 

 rejected, not only as an exposition of the actual state of things, 

 but even as a representation of the results of Brewster's own 

 observations. 



Brewster's observations were subsequently published in the 

 ' Transactions of the Royal Society of Edinburgh/ 1864, vol. xxiii. 

 p.213,and in the Philosophical Magazine for August 3865, p. 11 8. 



* Communicated by the Author, being the substance of a paper read 

 before the Ashmolean Society, Oxford, in March 1875. 



Phil. Mag. S. 4. No. 334. Suppl. Vol. 50. 2 K 



