

1/ 



/ 



7 



56 Prof. Haidinger on the Polarization of Light by Vapour. 



equal to about 12°, its central line being nearly at the angular 

 distance of 41° from the centre. But I must claim for these 

 angular values only the character of approximations, as I could 

 only note the data from memory, and did not succeed in getting 

 another sight of the phenomenon. 



" In the situation fig. 3, looking at the column of air loaded 

 with vapour and obliquely 

 illuminated by the sun en- 

 tering through a small win- 

 dow, the transverse brushes 

 of polarization produced by 

 transmission were distinctly 

 visible at a, while from the 

 wet boards of the floor at b 

 the polarization of reflection 

 was as distinctly visible in 

 the longitudinal brushes. 



" In a manner somewhat 

 analogous to the preceding 

 observations, the tangential 

 or transverse brushes of po- 

 larization may be observed 

 near the sun in vapoury air, 

 while the sun itself is screened from the eye of the observer by 

 intervening objects." 



You see, my dear Sir, I have reported only the bare observa- 

 tion, and that only for the sake of following up the " brushes of 

 polarization." But I have not found myself either sufficiently 

 prepared nor prompted by circumstances to follow up the 

 study of the subject itself in the manner it well deserves. You 

 are now in the course of the most interesting inquiries ; and I 

 should be happy to find that you would give some kind glance 

 at my own long ago brought forward and now nearly antiquated 

 endeavours. 



I still retain the most lively recollection of your friendly visit 

 at my house in Vienna in 1856, when I still was laid up in my 

 bed from the cold I had caught the first day of the opening of 

 our scientific association. And greatly interested I was at so 

 many of your investigations, several of which I had the good 

 luck to quote in confirmation of my humble contributions. Per- 

 haps I should have written this letter in German, so completely 

 are you master of my own language, but I thought this mode of 

 writing would be more in agreement with your daily general 

 practice and intercourse. 



Believe me ever, my dear Sir, 



Yours very truly, 



W. Haidinger. 



