and Saccharine Solutions exercise on Heat. 471 



Tube 0'05 millim. long. 

 Deviations. 

 Sparat +33degi-ees . 611 Rotation - 10° 26'. 

 ... — oo ... . o-lj 



Same conditions ; tube 0*1 millim. long. 



Sparat +18°-5 . . . 11-5| Rotation -20° 25'. 

 — 71 'o . . . rb ) 



Same conditions; tube 0*15 millim. long. 



Sparat^Odegi-ees . . 24-8 j_ Rotation +32° 33'. 



The law of lengths exhibits itself here also ; and we observe, 

 as in the case of lights that the absolute magnitude of the rota- 

 tion increases with the refrangibility. 



The diminution is the same as long as we do not operate on 

 the rays immediately bordering upon the obscure portion of the 

 spectrum. Near this limit an apparent diffex'ence is exhibited, 

 which, however, is easy to be explained. The calorific rotation 

 appears notably less than the optic rotation ; in some experiments 

 with a column of turpentine 0'05 millim. long, the rotations of 

 light and heat have diifered more than two degrees. 



This fact can also be proved in -the following manner: — 



With a column of the essence 0*15 millim. long it was neces- 

 saiy, in order to extinguish the red image as effectually as pos- 

 sible, to turn the analyser to +40 degrees from its primitive 

 position. In this position the thermoscopic apparatus indicated 

 a deviation of 0"6. It was necessary to tm-n the spar to about 

 57 degrees before the galvanometer ceased to be affected ; at 

 this point, however, the luminous image was very visible. 



It appears to us that this difference may be accounted for in 

 the following manner. 



The bundle of calorific rays on which we operated having a^ 

 certain width, was formed in the case under consideration partly 

 by the extreme and visible red rays, and partly by the obscm'c 

 rays. When the rotation of the heat was determined, the 

 obscure portion, on account of its intensity, was predominant, 

 and the angle corresponding to this portion was found. For the 

 rotation of the luminous portion, on the contrary, that of the 

 visible rays of the image was necessarily found : the latter there- 

 fore ouglit to be the greater of the two ; since, according to the 

 law established by M. Biot, the red rays have a greater refran- 

 gibility tlian the obscure rays. 



In our experiments, we have in some instances pursupd a 

 method somewhat different from that which has been just ex.- 

 plained. 



