2-14 



Intelligence and Miscellaneous Articles, 



rized light to traverse the vapour. After many fruitless attempts, 

 Biot finally succeeded in establishing the existence of the rotatory 

 power of the vapour of the oil, when an explosion and a fire destroyed 

 his apparatus. Either hecause this experiment presented too many 

 dangers, or because its arrangement appeared too difficult, it has not 

 been repeated since 1818. It remained, however, to inquire if the 

 rotating power is the same in magnitude and in direction in the 

 vapour and in the liquid which has produced it ; nor was it uninter- 

 esting to determine the law of dispersion of the planes of polariza- 

 tion of rays of various colours under these two different conditions. 

 Such was the object of my researches, which doubtless I could not 

 have executed without the kind encouragement of MM. Pasteur 

 and Verdet, and the resources which the laboratory of the Ecole 

 Norinale Superieure presented. 



Some preliminary experiments made with the vapours of essence 

 of turpentine and of camphor, by means of a tube 15 metres in length, 

 heated by a series of gas jets, showed that the rotatory power pre- 

 vails in vapours in the same direction as in liquids. The magnitude 

 of the rotation was sufficient to allow me to reduce the length of 

 the tube to 4 metres, and to arrange it so that the temperature was 

 uniform from one end to the other. But working upon liquids of 

 considerable rotatory power, I could see that the numbers represent- 

 ing the molecular rotatory powers of the vapours were much less 

 than those corresponding to liquids condensed at the ordinary tem- 

 perature ; I was thus led to investigate whether the molecular rota- 

 tory power of these essences did not vary with the temperature. 



These liquids were examined at various temperatures, with special 

 apparatus, and by methods the description of which will be found 

 elsewhere. I will merely remark that I decided to work on 

 essences as homogeneous as possible ; and as liquids always slightly 

 alter when kept for several hours at high temperatures, I commenced 

 these determinations at lower temperatures. 



Representing by (a) the molecular rotatory power at the tempe- 

 rature /, the determinations made up to 160° are contained in the 

 following formulas : — 



Rays. 



Essence of orange values 

 of (a). 



Essence of bigarade values 

 of (a). 



Essence of turpentine 

 values of (a). 



c 



D 

 E 

 F 

 G 



90-45 - 0-0893/ -0 000054/ 2 

 115-91 -0-1237/- 0000016/ 2 

 148-82-0-1585/-0-00U028/ 2 

 180-67-0-1979/-0-000001/ 2 

 241-20-0 2331/-0-000181/ 2 



92-79-0-1041 /- 0-000106/ 2 

 118-55-0-1175/-0-000216/-' 

 153-81-0-1667/-0 000198/ 2 

 186-89-0-2162/-0000152/ 2 

 249-33- 0-2638/- 0-000403/ 2 



28-29-0-003187/ 

 36-61-0-004437/ 

 46-29-0006187/ 

 5500-0007000/ 

 7101-0008437/ 



The molecular rotatory power may thus be expressed as a function 

 of the temperature by the parabolic formula a — bt — ct 2 , a being very 

 small for the essences of orange and bigarade, and virtually zero for 

 essence of turpentine. 



If the values of (a) are compared for the same temperature and for 



