THE 



LONDON and EDINBURGH 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[THIRD SERIES.] 



MARCH 1833. 



XXV. Remarks on Mr. Potter's Experiment on Interference. 

 By G. B. Airy, Esq. Professor of Astronomy and Experi- 

 mental Philosophy in the University of Cambridge. 



To the Editors of the Philosophical Magazine and Journal. 

 Gentlemen, 



T N the last Number of your Journal is a paper by Mr. Pot-. 

 ■*■ ter upon certain phenomena of Interference, which he con- 

 siders to be inexplicable on the theory of undulations. These 

 phaenomena are, in fact, a confirmation of the truth of that 

 theory, and might have been predicted from the theory. I 

 should not therefore have troubled you with these remarks, if 

 I did not feel that the public is much interested in seeing a 

 distinct and correct interpretation put upon experiments 

 and calculations like those to which I allude; and if I were 

 not convinced that Mr. Potter, whose labours as an experi- 

 mentalist I value most highly, would feel any thing but pain 

 at my pointing out the error into which (I conceive) he has 

 fallen as a theorist. 



In Mr. Potter's experiment two pencils of light originating 

 from a common source are made to interfere by falling upon 

 two plane mirrors inclined at a small angle : the two reflected 

 pencils fall upon a prism whose edge is parallel to the line of 

 junction of the mirrors, and the interference-fringes, after 

 emergence, are examined by means of an eye-glass in the usual 

 manner. The light being supposed homogeneous, Mr. Pot- 

 ter finds (correctly) from the theory of undulations that the 

 points, at which the paths of the pencils from the two images 

 are equal, are almost exactly at the centre of the mixture 



Third Series. Vol. 2. No. 9. March 1833. Y 



