Royal Society* 219 



the different Media by which they are reflected, refracted or ab- 

 sorbed." By Joseph Power, Esq., M.A., Fellow of Clare Hall and 

 Librarian of the University of Cambridge, &c. 



For the train of thought which suggested the considerations in 

 this communication, the author states that he is more particularly 

 indebted to the researches of Professor Draper of New York, con- 

 tained in his work " On the Organization of Plants, the Chemical 

 effects of the Solar Rays," &c, his experiments tending 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 pheno- 

 mena of the sun-beam, so that the latter cannot be reflected, re- 

 fracted, much less absorbed, without producing some effect upon the 

 recipient medium. Whilst however he acknowledges the informa- 

 tion he has received from that work, he differs in opinion with its 

 author, as to the necessity of admitting 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 aether is capable, and which, in the case of the 

 sun-beam, are impressed upon it at the surface of the sun. He con- 

 siders that the vis viva, which has its origin in these vibrations, is 

 transmitted through the aether, with the velocity of light, in extremely 

 minute undulations of different lengths and periods. If then a sun- 

 beam, fraught with a vast variety of such undulations, be incident 

 upon a medium so constituted that particles are capable of vibrating 

 in unison, or even in harmonious consonance less perfect than uni- 

 son, with some or other of the aethereal 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 Reso- 

 nance. He states that there may be a difficulty in explaining, but 

 there can be no doubt of the fact, that the vis viva due to such in- 

 duced vibrations may, like those of heat, become more or less per- 

 sistent in the medium, producing at one time the phaenomenon of 

 fixed chemical action ; at another that of permanently latent heat ; ' 

 at another that of less permanently latent or retarded heat ; at an- 

 other that of coloration and absorption; at another that of phos- 

 phogenic action. The remarkable phaenomena lately discovered by 

 Professor Stokes seem to him to be closely allied to the latter, differ- 

 ing however in the circumstance that they cease to exist the moment 

 the exciting rays are withdrawn. Guided by analogy, he is, however, 

 inclined to think that these phaenomena will be found hereafter to 

 possess some slight though insensible duration, while he regards all 

 action which is reaiiy momentary as expending itself upon the pass- 

 ing rays as they emerge in the form of reflected or refracted rays. 



But all these effects, of whatever kind, the author regards as due 

 to one and the same cause, which can be no other than the expen- 

 diture or distribution of the vis viva originally derived from the sun, 

 and conveyed by the aether. Such expenditure he considers we may 

 regard as of two kinds, according as the vis viva is retained by the 

 medium, or transmitted with the emergent rays. If it be expended 

 solely upon the emergent rays, the vis viva of the incident ray ought 



