THE 

 LONDON, EDINBURGH and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



SUPPLEMENT to VOL. XXXV. THIRD SERIES. 



LVIII. On the Rotation of the Plane of Polarization of Heat 

 by Magnetism, By MM. F. de la Provostaye and P. 

 Desains*. 



SHORTLY after the brilliant discovery of Prof. Faraday 

 of the rotation of the plane of polarization of light by 

 magnetism, M. Wartmann announced f that he had tried the 

 same experiment with radiant heat. He employed the heat 

 of a lamp, which he partially polarized by making it pass 

 through two piles of mica crossed at right angles. The elec- 

 tro-magnets and a cylinder of rock-salt were placed between 

 these piles, and consequently very near the thermo-electric 

 apparatus. The galvanometer, on the contrary, to be pre- 

 served from the action of the electro-magnets, was removed 

 to a great distance ; but the result was a considerable increase 

 in the length of the circuit, and a diminution of sensitiveness. 



Notwithstanding all these inconveniences, which he clearly 

 pointed out, and which he was not able to overcome, M. Wart- 

 mann thought he observed that the needle of the galvanometer, 

 after having attained a fixed deviation under the influence of 

 the radiation not intercepted by the piles of mica, was again 

 displaced and took a fixed position different from the first* 

 when the current was established, which seemed to indicate a 

 rotation of the plane of polarization of heat. 



At Paris, some persons having vainly attempted to repro- 

 duce these phaenomena, we have considered that it would 

 be useful to revert to these experiments, and to point out a 

 method which permits of making them succeed with facility. 



We have introduced into M. Wartmann's process three prin- 

 cipal modifications: — 1st, we employ solar heat; 2ndly, we take 

 for polarizing apparatus two prisms of achromatic spar; Srdly, 

 and this appears to us indispensable, instead of placing the 

 principal sections at 90% we arrange them so that they make 

 an angle of nearly 4-5°. 



* From the Annates de Chimie et de Physique, October 1849. 

 t Institut, May 6th, 1846, No. 644. 



Phil. Mag. S. 3. No. 239. Suppl, Vol. .35. 2 I 



