IX. On a remarkable Modification of Newton's Rings. 

 By G. B. AIRY, M. A. F. R. Ast. Soc. F. G. S. 



PLUMIAN PROFESSOR OF ASTRONOMY AND EXPERIMENTAL PHILOSOPHY, 



LATE FELLOW OF TRINITY COLLEGE, AND FELLOW OF THE 



CAMBRIDGE PHILOSOPHICAL SOCIETY. 



[Read Nov. 14, 1831.] 



The following variation of the observation of Newton's coloured 

 rings will it is hoped be considered as conclusive, so far as it 

 goes, in favour of the undulatory theory of light. It was sug- 

 gested by a consideration of the values assumed in particular 

 cases by Fresnel's general formula for the intensity of reflected 

 light; experiment has entirely confirmed my anticipations: and 

 the fact appears to be perfectly inexplicable on any theory of 

 emissions. 



To begin with a case generally known, suppose that a convex 

 lens of great focal length is placed on another convex lens, or 

 on a plane glass, or on a concave glass where the radius of con- 

 cavity is greater than the radius of the convexity which rests 

 upon it: and suppose common light to fall on it, and to be received 

 by the eye after reflection. A set of rings is seen with a remark- 

 ably black spot in the center: considerable pressure being some- 

 times necessary to insure the blackness of the central spot. On 

 inclining the incident ray, the rings dilate, but the center remains 

 perfectly black, and continues so till the direction of the incident 

 light is parallel to the upper surface of the lens. 



