472 On the Rotary Potve)' which the Essence of Turpentine 



The analyser being always at zero after the interposition of 

 the active liquid, by a suitable rotation of the polarizing prism 

 we caused the luminous image to disappear ; turning the ana- 

 lyser successively to +45° and —4-5°, we observed the galvano- 

 metric deviations. If the rotation be the same as for the light, 

 these effects will be equal. If not, let S be their sum, and D 

 the smallest, which we will suppose to be that corresponding to 

 + 45° for instance, we have evidently 



and 



•^ equal to cos^ (45° + :r), 



g T) 



— ^ — equal to cos^ (45°— a;'), 



a; being the difference between the rotation of the ray of heat 

 and the angle to which the polarizing prism must be turned, to 

 cause the luminous image to disappear. 



These details suffice to explain the manner in which the fol- 

 lowing results have been arrived at : — 



r Optic rotation of the red I t^o ri( 

 Essence of turpentine, | luminous ray . . . j 

 tube 005 millim. long. ^ Kotation of the calorific I iio or/ 

 [_ ray which accompanies it J 



r Optic rotation of the cx-\ ^qo nf 

 Essence of turpentine, J treme red ray . . j 

 tube O'l millim. long. j Rotation of the calorific "1 ^qo of\t 

 [_ ray which accompanies it J 



We have also examined the rotary action of cane-sugar. For 

 this purpose we have made use of a very concentrated solution, 

 filling therewith the tube 0"05 millim. in length. 



For the extreme red, the rotation of the luminous ray was 25 

 degrees ; that of the calorific ray 22° 36'. 



We then divided the syrup into two parts exactly equal, and 

 replacing one of them in the tube, we filled it up with distilled 

 water. The rotation was then — 



For the light .... 12° 30' 

 For the heat . . . . 11° 20' 



We remark here, what has been before expressed, that, for 

 both sugar and essence, the calorific rotation was in the same 

 direction as the luminous rotation ; consequently to the right in 

 the one case, and to the left in the other. 



Finally, we were aware that, according to the indications of 

 M. Biot, a liquid formed by dissolving 31 parts of camphor in 

 69 parts of the essence of turpentine, causes almost the same 



