THE 
LONDON, EDINBURGH anv DUBLIN 
PHILOSOPHICAL MAGAZINE 
AND 
JOURNAL OF SCIENCE. 
[FOURTH SERIES.} 
DECEMBER 1857. 
XLVII. Experimental Relations of Gold (and other Metals) to 
Light.—The Bakerian Lecture. By Micuart Farapay, Esq., 
D.C.L., F.R.S., Fullerian Prof. Chem. Royal Institution, &c.* 
Ss eps wonderful production of the human mind, the undu- 
latory theory of light, with the phenomena for which it 
strives to account, seems to me, who am only an experimentalist, 
to stand midway between what we may conceive to be the coarser 
mechanical actions of matter, with their explanatory philosophy, 
and that other branch which includes, or should include, the 
physical idea of forces acting at a distance ; and admitting for 
the time the existence of the «ther, I have often struggled 
to perceive how far that medium might account for or mingle 
in with such actions, generally ; and to what extent experi- 
mental trials might be devised which, with their results and 
consequences, might contradict, confirm, enlarge or modify the 
idea we form of it, always with the hope that the corrected or 
instructed idea would approach more and more to the truth of 
nature, and in the fulness of time coincide with it. 
The phenomena of light itself are, however, the best and 
closest tests at present of the undulatory theory; and if that 
theory is hereafter to extend to and include other actions, the 
most effectual means of enabling it to do so will be to render its 
application to its own special phenomena clear and sufficient. 
At present the most instructed persons are, I suppose, very far 
from perceiving the full and close coincidence between all the 
facts of light and the physical account of them which the theory 
* From the Philosophical Transactions, Part I. for 1857; having leen 
received by the Royal Society Nov. 15, 1856, and read Feb. 5, 1857. 
Phil. Mag. 8. 4. Vol. 14. No. 95. Dee. 1857. 2D 
