THE 

 LONDON, EDINBURGH, and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[FIFTH SERIES.] 



JV OV EMBER 1881. 



XLL Experimental Investigations on Magnetic Rotatory Pola- 

 rization in Gases. By M. Henri Becquerel*. 



• [Plates VII. & VIIL] 



Introduction. 



TNTIL within the last few years all attempts to demon- 

 V>* strate the electromagnetic rotation of the plane of pola- 

 rization of light in passing through gaseous media have been 

 futile, and the phenomenon discovered by Faraday in solid 

 and in liquid bodies seemed in gases to escape all measure- 

 ment. The analogy presented in the case of dilute solutions 

 of certain substances had led to the supposition that the mag- 

 netic rotatory power of the same body remained nearly pro- 

 portional to its density at the moment of its passage from the 

 liquid to the gaseous state. Experiment has shown that this 

 is not the case ; and even whilst operating under conditions 

 of magnetic intensity apparently sufficiently powerful, several 

 experimentalists have been unable to observe any appreciable 

 rotation of the plane of polarization in light. 



My investigations, pursued now for several years, on mag- 

 netic rotatory polarization, have led to various conclusions 

 with regard to gases, which it was of great interest to verify, 

 and which enabled me to foresee the character of the rotations 

 to be observed, and the existence of a remarkable relation 

 between the index of refraction of bodies and their magnetic 

 rotatory power. Based upon these considerations, an appa- 



* From the Annates de Physique et Chimie, [5] xxi. p. 289. 



PhiL Mag. S. 5. Vol. 12. No. 76. Nov. 1881. 2B 



