516 Intelligence and Mincellaneuus Articles. 



ON THE POI^VRIZATION OF THE CHEMICAL KAYS WHICH EXIST IN 

 SOL.iR LIGHT. BY PROF. E. WARTMANN. 



It is well known that physicists have found in the solar spectrum, 

 produced by means of a good prism, three orders of radiations which 

 are in part superposed, the calorific, the colorific or luminous, and 

 the chemical. The rays of the two first orders are susceptible of 

 polarization*, and consequently of extinction. But the chemical 

 rays have not been examined in this respect ; and the following ex- 

 periments, made with the aid of a skilful artist of Laugannef , will 

 help to supply this deficiency. They were made on August 27, 1850, 

 from 2 to 3 o'clock in the afternoon, with a warm day and a clear sky. 



The polarizer was a Nicol's prism, 086 millim. long, 0-036 millim. 

 and 0'028 millim. wide. It was contained in a tin tube 'blackened 

 inside. Another similar tube contained the analyser, another Nicol's 

 prism, 0'07 millim. long, and the diagonals of which measured 0-03 

 millim. and 0-023 millim. The two tubes, the total length of which 

 was one metre, turned one in the other, and intercepted all light except 

 that which was to be examined. 



First Experiment. — A prepared plate coated with silver was ex- 

 posed to the vapour of iodine, afterwards to that of bromide of lime, 

 and again to that of iodine. It thus acquires an exquisite photo- 

 graphic sensitiveness. It was employed in taking a Daguerreotype 

 portrait. The person who sat was in the shade. Against the exter- 

 nal surface of the object-glass of the camera obscura, the two prisms 

 had been arranged, the principal sections of which formed an angle 

 of 45°. The impression obtained at the end of eighty seconds was 

 very clear and distinct. 



Second Experiment. — A silvered plate submitted to the same pro- 

 cess was substituted for the first. The principal sections of the 

 prisms were at right angles. After three minutes' exposure the eflfect 

 was absolutely null. 



Third Experiment. — Instead of the person a lithograph was placed 

 in the sun on a plane nearly perpendicular to the rays which illu- 

 mined it. The experiment was continued for seven minutes, but the 

 effect was still null. 



Fourth Experiment. — It was proved that, on the contrary, an ex- 

 posure of four minutes, under the same conditions, gave a very visible 

 image, when the angle of the principal sections was only 70°. 



It results from these experiments, that the chemical are polarized 

 like the luminous and the calorific rays under similar conditions. 

 The first were extinguished with the second ; it was out of the ques- 

 tion to employ them to obtain photogenic impressions of beings, 

 who, being unable to endure the brilliancy of the light, would 

 have been exposed to the factitious shadow of a proper analyser. — 

 Bibliotheqiie Universelle de Geneve, November 1850. 



* I discovered twenty months ago, that the atmospheric heat due to the 

 suu is polarized exactly like the light which comes to us from tliat planet. 

 The second part of the twelfth volume of the Memoirs of the Socie'te de 

 Physique et d'Histoire Naturelle de Geneve, now in the press, contains the 

 details of my researches on this subject. 



t M. Heer, brother of the celebrated professor of the University of Zurich. 



