470 On the Rotary Power which the Essence of Turpentine 



Same conditions ; length of tube O'l millim. 

 Deviations. 

 Spar at^O degrees . . 10-4\ Rotation 39° 22'. 



Anothei- series. Same conditions ; tube 01 millim. long. 

 Spar at^O degrees . . 14-0| Rotation 40° 12'. 



Tube 0'15 millim. long. 

 Spar at degrees . . 4-9\ Rotation 59° 13'. 



..• yu ... . . io'oj 



These numbers satisfy the law of lengths. Further, the ob- 

 servation of the optic rotation, obtained for the same light and 

 with the same tubes, shows that its absolute value was the same 

 as that of the calorific rotation. 



We have also determined the rotary action of a column of 

 turpentine 0-05 millim. in length ; but the smallness of the 

 effect obtained at 90 degrees, that is to say, when the principal 

 section of the analyser was perpendicular to the plane of primi- 

 tive polarization, compelled us to choose two other rectangular 

 positions. 



Tktbe 0"05 millim. long. 

 Deviations. 

 Spar at -65 degrees . 9^8^^ Rotation -20°. 



These experiments prove that the altered plnne of polarization 

 was at — 20° ; they therefore differ very little from the preceding 

 experiments, which, according to the law of lengths, would place 

 the rotation at 19° 45'. 



Same conditions; tube O'l millim. long. 

 Deviations. 

 Spar at + 5 degrees . 8-25 \ Rotation -40°. 

 — 85 ... . 8-2oJ 



The altered plane of polarization is here 40 degrees from zero. 

 The rotation is therefore double of that produced by the pre- 

 ceding tube mth the same heat. 



These experiments were repeated with the heat which accom- 

 panies the extreme red of the solar spectrum, the essence of tur- 

 pentine being still employed as the active liquid. The results 

 were as follows : — 



