and Saccharine Solutions exercise on Heat. 467 



Since then, in a new investigation inserted in the Annales de 

 Chimie et de Physique, 3i'cl series, vol. xi. p. 109, M. Biot adds, 

 " It has not yet been investigated whether the same property of 

 modifying calorific rays be possessed by those liquids which 

 exercise a rotary power on polarized light ; and it would be of 

 much interest to establish the identity or the dissimilarity of 

 action in this case, where it is purely molecular." We have un- 

 dertaken the solution of this question, and now propose to exhibit 

 the results to which our inquiries have conducted us. 



In all our experiments we have operated with polarized solar 

 heat, simplified as much as possible by refraction. To obtain it 

 in this state, we dispersed, by means of a very pure prism, a solar 

 pencil transmitted successively through a narrow chink and a 

 ciystal of Iceland spar. The spectrum thus obtained was sufii- 

 ciently clear to exhibit the lines of Fraunhofer. In isolating in 

 this spectrum the rays of a determinate colour, it was easy to 

 satisfy ourselves that the polarization was complete. For this 

 purpose it was sufficient to receive the rays on a second analysing , 

 prism, where they became bifurcated, and gave two images, one 

 of which disappeared when the principal section was parallel or 

 perpendicular to that of the polarizing prism. 



During the rotation of the analyser one of these images re- 

 mained fixed, and passing through a conveniently situated open- 

 ing, fell upon the pile of the thermic apparatus. We have assured 

 ourselves by frequent repetitions, that, when the analysing prism 

 is turned, the intensity of the calorific effect, produced by the 

 action of this image upon the apparatus, varies exactly according 

 to the law of Malus. As the methods which we have adopted 

 to measure the rotations presuppose this law, we will first cite 

 some numbers obtained in the preliminary experiments. A con- 

 fii'mation of the results which we obtained last year in operating 

 with the heat which accompanied white solar light, is in this 

 case exhibited. 



Experiments made with the heat which accompanies the extreme 



red rays. 

 Position of the principal section of the analyser. Deviations. Ratio. 

 Parallel to the i.dane of primitive polari-"! 



zation ......./ ^•^■^^|o-50 



At 45 degrees to the right or to the left^ ^ , .^j-, [ 

 of the plane of polarization . . j -^ 



Parallel to the plane of polarization . . IG'5 ~l ,. -,.. 



At 30 degrees to the right or left 



Parallel to the plane of polarizatio 

 At 45 degrees to the i-ight or left 



Parallel to the plane of polarization . . 15'7 \n.7Q0 

 At 30 degrees to the right or left . . 11-5 J ^ ''^'^ 



Parallel to the plane of polarization . . 159 \n.Kn 



