(t ^ ''.'•" r/ THE 



ve4,bND.Q]:^'"EDINBURGH and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[THIRD SERIES.] 



NOVEMBER 1845. 



XLIX. A Theoretical Explajiafion of the Aber7'atio7i of 

 Light. By the Rev. J. Challis, M.A.^ Plmnian Professor 

 of Astronomy in the University of Cambridge'^. 



\ T the meeting of the British Association held at Cani- 

 "^^ bridge last June, I brought forward a theory of the 

 aberration of light, the same in principle as that which forms 

 the subject of this communication, but requiring some eluci- 

 dation with respect to its applicability on the undulatory hy- 

 pothesis of light. My present object is to show how it applies 

 on that hypothesis, and for this purpose I proceed to state, 

 first, the general principle of the theory. 



Let 5 and w (fig. 1) be simulta- 

 neous positions of two visible ob- 

 jects, one of which, 5, is fixed in 

 space while the other is carried by 

 the earth's motion with the eye of 

 the spectator. For instance, s may 

 be a star, and w the wire of a tele- 

 scope. Let the straight line joining 

 the positions s and tw be produced 

 to meet the straight line e^e^, in 

 which the spectator's eye is moving 

 in the point e?. Take ^ e to e'tio in 

 the ratio of the earth's velocity to 

 the velocity of light ; and let e and 

 TO be simultaneous positions of the eye and the object la. Now 

 the light which started from w in the direction w^ at the in- 

 stant the eye was at e, arrives, in company with light from 5, at 

 ^ when the eye comes to the same point; and the eye receives 

 the impression that to and s are in the same direction, because 

 it receives light from each object proceeding in the common 

 • Communicated by the Author. 

 PhU. Mag. S. 3. Vol. 27. No. 1 8 L Nov. 184-5. Y 



