Intelligence and Miscellaneous Articles. 



245 



the different rays of the spectrum, it is seen that the essences of 

 orange and of bigarade diverge much more than essence of turpen- 

 tine from the law of the inverse ratio of the square of the wave- 

 length ; the product (a)A 2 varies in fact from the ray C to the ray 

 G by about one-seventh of its value in the case of essences of orange 

 and of bigarade, while the variation is only one-fifteenth in the case 

 of essence of turpentine. 



The ratio of the rotatory powers for the same ray is taken at any 

 two temperatures ; it is found to be the same whatever ray of the 

 spectrum be considered ; it is thus easily deduced that the law of 

 the dispersion of the planes of polarization of rays of different colours 

 is the same for all temperatures, 



The preceding liquids, like camphor, were brought to the state 

 of vapour in a tube 4 metres in length, surrounded by a jacket, 

 which could be raised to any temperature by means of a series of 

 gas-jets. I measured the rotations produced by this column of 

 vapour, and I compared them with those that would be produced by 

 a certain length of the liquid arising from the condensation of the 

 vapour. The following Table refers to this series of experiments : — 



; Essence of orange. 



Essence of bigarade. 



Essence of turpentine- 



Camphor. 











| Va- ' Li- 

 | pour. quid. 



Ratio. 



Va- 

 pour. 



7 



quid. Ratio - 



Va- Li- 

 pour, quid. 



Ratio. 



Va- 

 pour. 



Li- i • 



quid. ! Ratl °- 





/!/ 





I 



\\\ 





/ 



J 





c 



o o 









7-74 



36-08 4-66 



4°-36 13-03 



2-99 



6°-89 



19°43 



2-82 



D 



12-10 45-97 



4-14 



9-83 



4606 4-69 



5-57 16-59 



2-98 



9-44 



26-71 2-83 



E 



1439 5957 



415 



12-75 



59-54 4-67 



7-09 21-08 



2-97 



13-36 



37-82 



2-83 



F 



17-46 72 24 



4-14 



15-37 



71-61 4-66 



8-36 24-96 



2-99 



1 7*7 



5012 



2-82 



G 



23-44 97-19 



415 



20-75 



96-63 4-66 



10-96 32-68 



2-98 



28-11 



79-62 



2-83 



The ratio of the rotations for the same ray in the two conditions 

 is the same for all rays of the spectrum, the difference being less 

 than the errors of observation ; hence it may be concluded that the 

 law of dispersion is independent both of the temperature and of the 

 condition of the body. 



It remained to follow the variation of the molecular rotatory 

 power after the change of condition. For this determination, which 

 necessitates experimental precautions that I cannot here enumerate, 

 I used the observation of the sensible tint, the use of which is justi- 

 fied by the preceding. The measurement being made when the 

 tube was saturated with vapour at a known temperature and pres- 

 sure, the vapour was expelled by a current of carbonic acid ; it was 

 condensed, and the molecular rotatory power of the liquid deter- 

 mined at various temperatures. For essence of turpentine and for 

 camphor, the molecular rotatory power of the vapour is almost 

 exactly the same as that of the liquid supposed to be at the same 

 temperature ; for the essences of orange and of bigarade it is a little 



