RELATION OF LIGHT TO THE MAGNETIC FORCE. 
15 
iii. General considerations. 
2221. Thus is established, I think for the first time*, a 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, dif- 
ficult 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, perhaps, 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 phenomena in particular forms, is here further iden- 
tified and recognised, by the direct relation of its form of light to its forms of electri- 
city and magnetism. 
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 properties 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 phenomena of electric induction and electrolyzation show a vast supe- 
riority in the energy with which electric forces can act as compared to magnetic 
forces, so here, in another direction and in the peculiar 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 
* I say, for the first time, because I do not think that the experiments of Morrichini on the production of 
magnetism by the rays at the violet end of the spectrum prove any such relation. When in Rome with Sir 
H. Davy in the month of May 1814, I spent several hours at the house of Morrichini, working with his 
apparatus and under his directions, but could not succeed in magnetising a needle. I have no confidence in 
the effect as a direct result of the action of the sun’s rays ; but think, that when it has occurred it has been 
secondary, incidental, and perhaps even accidental ; a result that might well happen with a needle that was pre- 
served during the whole experiment in a north and south position. 
January 2, 1846. — I should not have written “for the first time” as above, if I had remembered Mr. Chris- 
tie’s experiments and papers on the Influence of the Solar Rays on Magnets, communicated in the Philoso- 
phical Transactions for 1826, p. 219, and 1828, p. 379. — M. F. 
