( 11 ] 
II. Theory of the Reciprocal Action between the Solar Rays and the different Media 
by which they are reflected , refracted, or absorbed ; in the course of which various 
optical laws and phenomena are elucidated and explained. By Joseph Power, 
M.A., Fellow of Clare Hall, and Librarian of the University of Cambridge : 
Member of the Cambridge Philosophical and Antiquarian Societies, and Founda- 
tion Fellow of the Society of Northern Antiquarians at Copenhagen. Communi- 
cated by the Rev. J. Cape, F.R.S. 
Received May 26, — Read June 9, 1853, — Revised by the Author, March 1854. 
1. FOR the train of thought which suggested the following considerations, I am 
more particularly indebted to the researches of Professor Draper of New York, con- 
tained in his remarkable work, “ On the Organisation of Plants, the Chemical Effects 
of the Solar Rays, &c.,” 2nd edit., New York, 1845. His experiments tend to show 
that the law of action and reaction, which prevails so generally in other departments of 
nature, is no less true in all the varied phenomena of the sunbeam, so that the latter 
cannot be reflected, refracted, much less absorbed, without producing some change 
upon the recipient medium. 
2. Whilst however I acknowledge my obligations to the author for the information 
I have derived from his excellent work, I wish carefully to guard against the infer- 
ence that I agree with him as to the necessity of admitting the existence of more 
than one imponderable, being strongly of opinion that all the effects of the solar 
rays may be attributed to some or other of the infinite variety of undulations of which 
the universal ether is capable, and which in the case of the sunbeam are impressed 
upon it by vibrations at the surface of the sun. 
3. The vis viva, which has its origin in these vibrations, is transmitted through 
the ether with the velocity of light in extremely minute undulations of different lengths 
and periods. 
If then a sunbeam, fraught with a vast variety of such undulations, be incident 
upon a medium so constituted that its particles are capable of vibrating in unison, or 
even in harmonic consonance less perfect than unison, with some or other of the 
ethereal vibrations of the incident beam, it must necessarily happen that one system 
of vibrations will be called into existence by the other according to the laws of 
resonance. 
There may be a difficulty in explaining, but there can be no doubt of the fact, 
that the vis viva due to such induced vibrations, like that which is due to the vibra- 
c 2 
