Intelligence and Miscellaneous Articles. 371 



Another way of producing this cross depends on the fact that 

 glass becomes doubly refracting by pressure. In pressing, there- 

 fore, a lens against a plate of glass, all the conditions for the cross 

 are fulfilled. A little contrivance for this purpose was described 

 by me in Carl's Bepertorium, vol. iii. p. 376. 



I am, Grentlemen, 



Tours faithfully, 



Yiktor v. Lang. 



ON THE MAGNETIC ROTATORY POWER OF VAPOURS. 

 BY E. BICHAT. 



By causing the current supplied by 80 large Bunsen cells to act 

 upon a ray of polarized light traversing vapour of sulphide of carbon, 

 I ascertained an evident rotation of the plane of polarization. The 

 rotation was very slight, not exceeding 15'. The first experiments 

 which led me to the result I have just indicated were made in the 

 course of the month of July 1878. 



The apparatus was constructed by M. Ducretet, of Paris. It 

 consists of two concentric tubes of 3*6 metres length. The inner 

 tube is closed by parallel glass plates, and carries two tubulures 

 furnished with cocks permitting it to be put in communication with 

 the outside. In the annular space comprised between the two 

 tubes a current of hot water, or a current of oil, or a current of 

 vapour can be made to circulate. For a length of 3 metres the 

 tube carries a series of bobbins covered with wire 3 millims. in 

 diameter. Experience shows that under these conditions the action 

 of the current upon the glass plates is nil. 



By means of the same instrument I have been able to prove in 

 the same manner an evident action of the electric current upon 

 polarized light passing through the vapour of bichloride of tin. 



I have done more : I have followed, step by step, from zero to 

 the temperature of ebullition, the rotation of the plane of polariza- 

 tion produced by one and the same current acting on sulphide of 

 carbon and bichloride of tin. I have thus ascertained that the 

 molecular rotatory power is maintained as long as the vicinity of 

 boiling-point of the liquid is not reached. At that moment there 

 is a diminution much more rapid than could have been foreseen 

 from the calculation based on the knowledge of the ratio of the 

 densities. 



I should have liked, before publishing the results of these 

 researches to be able to establish in a rigorous fashion the relation 

 that exists between the magnetic rotatory power of a liquid and 

 the rotatory power of its vapour. For this it would have been 

 necessary to be able to augment the action produced by the latter, 

 and at the same time to improve the measuring-processes. It has 

 not yet been possible for me to do so. I nevertheless hope soon to 

 overcome the difficulties which have hitherto stopped me. 



If I decide to publish now these still incomplete results, it is 



