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XLVIII. JNrw Magneto- Optic Phenomena exhibited by Magnetic 

 Solutions. By Dr. Quirino Majorana*. 



1. f^\ UIDED by the analogy between magnetic and elec- 

 VJT trie phenomena, I wished to determine whether a 

 magnetic field was capable of rendering a magnetic substance 

 doubly refracting, as an electrostatic field is capable of doing 

 in the case of a dielectric (Kerr's phenomenon). I was thus 

 led to the discovery of the following three effects : — 



(1) Magnetic Double Refraction. 



(2) Magnetic JJichroism. 



(3) Certain rotations of the plane of polarization of light, 

 which I have called Bimagnetic Rotation. 



2. Magnetic Double Refraction. — Experiments on highly 

 magnetic substances, such e. g. as thin transparent sheets of 

 iron, or solutions of ferric chloride, did not yield any appre- 

 ciable results. But solutions of ferrous chloride were rendered 

 feebly doubly-refracting when placed in a very intense mag- 

 netic field. The experiment was conducted in the following 

 manner. The liquid having been placed in a magnetic field, 

 a ray of light was allowed to pass through it in a direction 

 normal to the lines of force. The liquid was placed between 

 two crossed nicols whose principal sections made angles of 

 45° with the lines of force. On exciting the field, the light 

 re-appeared. With a field intensity of 18,000 c.G.s. units, if 

 the liquid was placed in a tube 7 cms. long, the double re- 

 fraction represented at most 2 to 3 hundredths of the wave- 

 length of yellow light. On the other hand, dialysed iron or 

 colloidal solution of ferric oxide was frequently strongly active. 

 The degree of activity varied according as the substance was 

 more or less freshly prepared. Thus freshly prepared dialysed 

 iron is entirely inactive, while if it is kept for a long time 

 (ten years or more), the double refraction, under the experi- 

 mental conditions indicated above in connexion with ferrous 

 chloride, reaches a value- of 12 wave-lengths of green light. 

 Dialysed iron thus aged was obtained from old bottles of 

 fer Bravais in a druggist's shop. 



The magnetic double refraction exhibited by dialysed iron 

 presents numerous peculiarities. It may be either positive or 

 negative ; but if the specimen of the liquid is very old, the 



* Communicated by the Author. This note forms a brief resume of 

 some researches of mine described more in detail in the Rendiconti delict 

 Accademia dei Lincei. at the meetings of May 31, June 15, August 3 

 and 17, 1902. I think that some observations contained in a short 

 notice of Dr. J. Kerr (Report Brit. Assoc. 1901, p. 868), with which I 

 became acquainted after the publication of my researches, must be 

 referred to the phenomena there described. 



