MAGNETISM. 129 



city, produce heat, light, and chemical affinity. Motion it can 

 directly produce under the above conditions ; i.e. a magnet 

 being itself moved will move other ferreous bodies ; these will 

 acquire a static condition of equilibrium, and be again moved 

 when the magnet is also moved. By motion or arrested mo- 

 tion only, could the phenomena of magnetism ever have become 

 known to us. A magnet, however powerful, might rest for 

 ever unnoticed and unknown, unless it were moved near to 

 iron, or iron moved near to it, so as to come within the sphere 

 of its attraction. 



But even with other than either magnetic or electrified 

 substances, all bodies will be moved when placed near the 

 poles of very powerful magnets some taking a position axi- 

 ally, or in the line from pole to pole of the magnet ; others 

 equatorially, or in a direction transverse to that line the 

 former being attracted, the latter apparently repelled, by the 

 poles of the magnet. These effects, according to the views 

 of Faraday, show a generic difference between the two classes 

 of bodies, magnetics and diamagnetics ; according to others, 

 a difference of degree or a resultant of magnetic action ; the 

 less magnetic substance being forced into a transverse position 

 by the magnetisation of the more magnetic medium which 

 surrounds it. 



According to the view given above, magnetism may be 

 produced by the other forces, just as the vanes in the instance 

 given are definitely deflected, but cannot produce them ex- 

 cept when in motion : motion, therefore, is to be regarded in 

 this case as the initiative force. Magnetism will, however, 

 directly affect the other forces light, heat, and chemical 

 affinity, and change their direction or mode of action, or, at 

 all events, will so affect matter subjected to these forces, that 

 their direction is changed. Since these lectures were deli- 

 vered, Faraday has discovered a remarkable effect of the 

 magnetic force in occasioning the deflection of a ray of 

 polarised light. 



If a ray of polarised light pass through water, or through 

 any transparent liquid or solid which does not alter or turn 

 aside the plane of polarisation, and the column, say of water, 



K 



