Nov. 1845.] Relation of Light to the Magnetic Force. 311 



true, direct relation and dependence between light and the 

 magnetic and electric forces ; and thus a great addition made 

 to the facts and considerations which tend to prove that all 

 natural forces are tied together, and have one common origin 

 (2146.). It is, no doubt, difficult in the present state of our 

 knowledge to express our expectation in exact terms ; and, 

 though I have said that another of the powers of nature is, in 

 these experiments, directly related to the rest, I ought, per- 

 haps, rather to say that another form of the great power is 

 distinctly and directly related to the other forms ; or that the 

 great power manifested by particular pheenomena in particular 

 forms, is here further identified and recognised, by the direct 

 relation of its form of light to its forms of electricity and mag- 

 netism. 



2222. The relation existing between polarized light and 

 magnetism and electricity, is even more interesting than if it 

 had been shown to exist with common light only. It cannot 

 but extend to common light; and, as it belongs to light made, 

 in a certain respect, more precise in its character and pro- 

 perties by polarization, it collates and connects it with these 

 powers, in that duality of character which they possess, and 

 yields an opening, which before was wanting to us, for the 

 appliance of these powers to the investigation of the nature of 

 this and other radiant agencies. 



2223. Referring to the conventional distinction before 

 made (2149.), it may be again stated, that it is the magnetic 

 lines of force only which are effectual on the rays of light, and 

 they only (in appearance) when parallel to the ray of light, or 

 as they tend to parallelism with it. As, in reference to matter 

 not magnetic after the manner of iron, the phaenomena of elec- 

 tric induction and electrolysation show a vast superiority in 

 the energy with which electric forces can act as compared to 

 magnetic forces, so here, in another direction and in the pe- 

 culiar and correspondent effects which belong to magnetic 

 forces, they are shown, in turn, to possess great superiority, 

 and to have their full equivalent of action on the same kind of 

 matter. 



2224. The magnetic forces do not act on the ray of light 

 directly and without the intervention of matter, but through 

 the mediation of the substance in which they and the ray 

 have a simultaneous existence ; the substances and the forces 

 giving to and receiving from each other the power of acting 

 on the light. This is shown by the non-action of a vacuum, 

 of air or gases ; and it is also further shown by the special 

 degree in which different matters possess the property. That 

 magnetic force acts upon the ray of light always with the same 



