[ ] 
X. The Bakerian 'Le.uiv'ke.— Experimental Belations of Gold {and other Metals) to 
Light. By Michael Faraday, Esq., D.C.L., F.B.S., Fullerian Prof. Chem. Pioyal 
Institution., Foreign Associate of the Acad. Sciences, Paris, Ord,. Boruss. pour le 
Merite, Eg., Memb. Boyal and Imp. Acadd. of Sciences, Petersburgh, Florence, Copen- 
hagen, Berlin, Gottingen, Modena, Stockholm, Munich, Bruxelles, Vienna, Bologna, 
Commander of the Legion of Honour, &c. &c. 
Eeceived Js’cvember 15, 1856, — Bead Tebraary 5, 1857. 
That wonderful production of the human mind, the undulatory 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 ether, 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 contra- 
dict, confirm, enlarge, or modify the idea we form of it, always with the hope that the 
corrected or instructed idea Avould 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 hght and the physical account of them which the theory supplies. If perfect, the 
theory would be able to give a reason for every physical affection of light ; whilst it does 
not do so, the affections are in turn fitted to develope the theory, to extend and enlarge 
it if true, or if in error to correct it or replace it by a better. Hence my plea for the 
possible utility of experiments and considerations such as those I am about to advance. 
Light has a relation to the matter which it meets with in its course, and is affected 
by it, being reflected, deflected, transmitted, refracted, absorbed, &c. by particles very 
minute in their dimensions. The theory supposes the light to consist of undulations, 
which, though they are in one sense continually progressive, are at the same time, as 
regards the particles of the ether, to and fro transversely. The number of progressive 
alternations or waves in an inch is considered as known, being from 37,600 to 59,880, 
and the number which passes to the eye in a second of time is known also, being from 
MDCCCLVII. X 
