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LXXVII. On the Equations applying to Light under the 

 action of Magnetism. By G. B. Airy, Esq., Astronomer 

 Royal. 



To the Editors of the Philosophical Magazine and Journal. 

 Gentlemen, 



"D Y the indulgence of Dr. Faraday, I have been able to 

 nr observe in the most satisfactory way the phaenomena of 

 the rotation of the plane of polarization of light passing 

 through boracic glass and other media under the action of 

 magnetic currents passing nearly in the direction of the light. 

 And in particular I have verified the very remarkable fact that, 

 upon passing the light successively in opposite directions 

 while the magnetic adjustments remain the same, the plane of 

 polarization undergoes the same change of position in regard 

 to space, or undergoes opposite changes of position in regard 

 to the expression of " rotation to the right," or " rotation to 

 the left," as referred to the eye of the observer. 



On reflecting upon the important fact that this change is 

 not produced except there be an intermediate diaphanous 

 body, it seems impossible not to conceive that the effect on 

 the light is produced mediately by the action of the magnetic 

 forces on the diaphanous body. The object of this commu- 

 nication is to point out what, as I conceive, must be the form 

 of the mathematical equations existing among the movements 

 of the particles of the glass, &c. or its contained aether, in 

 order to explain the phfenomena on mechanical laws. 



In order to justify my intruding upon you with a suggestion 

 which is exceedingly imperfect, I think it right to state to you 

 my opinion upon the present condition of the optical theory, 

 and upon several steps which, though leading to nothing con- 

 clusive, have nevertheless contributed to the real intellectual 

 progress of the science. 



On the truth of the undulatory theory, as regards the geo- 

 metrical representation of light by undulations based upon 

 transversal vibrations, the resolution of which into vibrations 

 at right angles to each other constitutes polarization, I have 

 not the shadow of a doubt. These undulations, whatever 

 may be the way in which they may have been originally cre- 

 ated, I conceive to be propagated by mechanical laws applying 

 to the attractive or repulsive forces of the particles of the 

 medium, the assumed aether, or the medium and the aether 

 combined. But I have seen no mechanical theory to which I 

 attach much importance or any unqualified belief. Never- 

 theless I think that the investigation and publication of these 

 mechanical theories have been advantageous to the science, 



