and Saccharine Solutions exercise on Heat. 473 



amount of rotation with rays of diiFerent refrangibilities. "We 

 filled a tube 0"10 millim. in length with a solution prepared in 

 this manner. The green and the red polai'ized rays experienced 

 in passing through it an equal rotation from right to left of 

 nearly 6^ degrees. The rotation of the calorific rays which 

 accompanied them was also the same, as may be seen from the 

 following numbers : — 



Heat which accompanies the green light. 



Deviations. 

 Spar at +40 degrees . . 5"1 

 ... -53 ... '. . 4-9 

 ... +40 ... . . 4-8 



It follows from this, that the deviations are the same at +40 

 degrees and at —53 degrees, and that thus the maximum devia- 

 tion had been observed at —6° 30'. 



Heat which accompanies the red light. 

 Spar at + 40 degrees . . 4-8 

 ... -53 4-7 



The laws of the phsenomenon are therefore the same for both 

 agents, and the identity throughout the details is most minute. 

 Thus, with regard to the rotaiy power, that which is tnie for a 

 ray of the luminous spectrum is also true for the calorific ray 

 which accompanies it. Now, according to the researches of 

 M. Biot, the rotations are nearly inversely proportional to the 

 squares of the access, or to the length of the imdulations ; so that 

 knowing the rotations experienced by two chffcrent rays in tra- 

 versing the same column of active liquid, and the wave-length 

 of one of them, that of the other can be found. In applying 

 this law to the rays of heat, we hope to be able to determine the 

 lengths of such and such rays of the obscure portion of the 

 spectrum. 



It is true that, according to the measurements of M. Broch, 

 {Repertorium der Physik, vol. vii. p. 115), the law of M. Biot is 

 not quite exact ; it will give, however, a first approximation. 



Phil. Mag. S. 4, Vol. 1 . No. 6. June 1851 . 2 K 



