THE 

 LONDON, EDINBURGH and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[THIRD SERIES.] 



FEBRUARY 1844. 



XIII. On the Undulatory Theory of Interference. By R. 

 Moon, M.A., Fellow of Queen's College, Cambridge, and of 

 the Cambridge Philosophical Society*. 



TN the following paper I shall endeavour to give a rationale 

 of the theory of interferences as explained upon undulatory 

 principles. I conceive that this is still a desideratum, for 

 though by adopting the hypothesis of secondary waves as a 

 basis for calculation, Fresnel has shown that a sufficiently 

 probable explanation may be given of that class of phaeno- 

 mena, it cannot be pretended that that explanation presents 

 to the mind any clear idea of the mode in which the pheno- 

 mena are actually brought about. Thus if we consider the 

 case of a succession of spherical waves emanating from the 

 same centre and incident upon an opake body, it is a natural 

 inquiry what becomes of each wave after diffraction. Can it 

 be possible that all trace is lost of the system of similar con- 

 centric waves? and if not, what is the nature of the modifica- 

 tions of those waves individually, and of their relations with 

 each other? 



It is in this point of view, in which the received explanation 

 affords no light, that I propose to attempt the elucidation of 

 the subject; and if the considerations I am about to submit 

 involve nothing either very new or very striking, they may 

 nevertheless be found to lead to conclusions equally simple 

 and important. 



Suppose then we have a single spherical wave diffracted at 



the edge of an opake object of indefinite extent, and suppose 



the wave to consist of a simple condensation followed by a 



rarefaction, it is obvious that immediately after passing the 



* Communicated by the Author. 



Phil. Mag. S. 3. Vol. 24. No. 157. Feb. 1844. G 



