T 11 E 

 LONDON, EDINBURGH and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[THIRD SERIES.] 

 JANUARY 1841. 



I. On the Diffraction of an Annular Aperture. By Georoe 

 BiDDELL Airy, Esq.^ M.A., F.ILS., Astronomer Royal. 



To the Editors of the Philosophical Magazine and Journal. 



Gentlemen, 

 T HAD no wish to make a communication to you which 

 •*- should assume the form of a discussion with Mr. Potter, 

 and I proposed, therefore, in adverting to the subject to which 

 Mr. Potter has alluded in your Number of October last, ra- 

 ther to add something to the investigation of a point which has 

 perhaps been passed over too lightly by writers on the Undu- 

 latory Theory, than to employ myself specially in indicating 

 what I consider to be the failing steps in Mr, Potter's reason- 

 ing. The calculations necessary for the first of these objects 

 were troublesome, and (with the little leisure that I can com- 

 mand) occupied a considerable time. Having, however, finished 

 these, I was preparing to address you when I saw Mr. Tovey's 

 paper in your Number for December. I am most happy to 

 find that the very clear explanation given by Mr. Tovey has 

 delivered me from the necessity of remarking on the reasoning 

 in Mr. Potter's paper, and I shall now proceed with my sup- 

 plementary investigation as an attempt at the extension of the 

 received theory. 



PnoBLEM. — A plane wave, whose exterior boundary is cir- 

 cular, is interrupted in its course by a circular plate, whose 

 plane is parallel to the front of the wave, and whose centre 

 coincides with the centre of the wave-boundary : it is required 

 to find the intensity of light at any point near the line which 

 is normal to the plate at its centre. 



Let a be the radius of the plate, h the radius of thebound- 

 Phil. Mag. S. 3. Vol. 18. No. IH. Jan. 18+1. B 



