Mr. G. G. Stokes on the AberratioJi of Light. 9 



When the liquid compound was treated with an alcohoHc so- 

 hition of potash, it was also resolved into benzoate of potash, 

 chloride ofpotassium, and a similar resinous matter, the quan- 

 tity of which appeared to be even greater than that yielded 

 by the solid compound. 



Neutral benzoate of lead, formed by adding a solution of 

 benzoate of soda to acetate of lead, was also subjected to de- 

 structive distillation. A small quantity of benzoic acid came 

 over mixed with a little of an aromatic oil, the smell of which 

 was quite different from that yielded by benzoate of copper. 

 I was unable, however, to detect the presence of any neutral 

 crystalline body. 



Glasgow, May 12, 1845, 



III. On the Aberration of Light. By G. G. Stokes, M.A., 

 Fellow of Pembroke College, Cambridge"^. 



nPHE general explanation of the phaenomenon of aberration 

 ■■ is so simple, and the coincidence of the value of the ve- 

 locity of light -thence deduced with that derived from obser- 

 vations of eclipses of Jupiter's satellites so remarkable, as to 

 leave no doubt on the mind as to the truth of that explana- 

 tion. But when we examine the cause of the phaenomenon 

 more closely, it is far from being so simple as it appears at 

 first sight. On the theory of emissions, indeed, there is little 

 difficulty ; and it would seem that the more particular expla- 

 nation of the cause of aberration usually given, which depends 

 on the consideration of the motion of a telescope as light passes 

 from its object-glass to its cross wires, has reference espe- 

 cially to this theory ; for it does not apply to the theory of un- 

 dulations, unless we make the rather startling hypothesis, that 

 the luminiftrous aether passes freely through the sides of the 

 telescope and through the earth itself. The undulatory theory 

 of light, however, explains so simply and so beautifully the 

 most complicated phsenomena, that we are naturally led to 

 rega. I aberration as a phaenomenon unexplained by it, but 

 not incompatible with it. 



The object of the present communication is to attempt an 

 explanation of the cause of aberration which shall be in ac- 

 cordance with the theory of undulations. I shall suppose that 

 the earth and planets carry a portion of the a3ther along with 

 them so that the aether close to their surfaces is at rest rela- 

 tively 40 those surfaces, while its velocity alters as we recede 

 * Communicated by the Author. 



