Proceedings of the British Association. 267 



aperture of the object-glass is made to vary from a quarter of an inch 

 to four inches. Hence it follows that the system of bands to 

 which Mr. Airy's theory is applicable has no existence in nature ; 

 that the phenomena which I discovered are still unexplained by the 

 Undulatory Theory, and may still be regarded as indicative of a new 

 species of polarity, till they are brought under the dominion of some 

 general principle. Since the publication of the two memoirs of Prof. 

 x\iry, I have devoted much time to the examination and measurement 

 of the bands under consideration, and I have been led to the obser- 

 vation, of many new and complex phenomena. I am still, however, 

 as ignorant as ever of the cause of the singular property to which 

 this notice relates, though I have succeeded in tracing the phe- 

 nomena to the true class of interferences to which they belong. 



The Astronomer Royal observed that this communication had 

 taken him by surprise. Until he saw the announcement in the jour- 

 nal of Sectional proceedings, about half an hour since, he was not 

 aware that Sir D. Brewster contemplated entering on the subject. 

 So imperfect was his memory on the subject, that he did not even 

 remember that the formulae read out by Sir D. Brewster were his. 

 The Section must therefore see that, under these circumstances, he 

 was totally unprepared to discuss the matter. — Sir D. Brewster 

 stated that he had sent the title of this communication to the Secre- 

 tary, in the prescribed manner, previous to the meeting, and he was 

 under the impression that the Astronomer Royal was aware of his 

 intention of calling the attention of the Section to the subject. He 

 now regretted that it had not occurred to him to write to Prof. Airy 

 on the subject. — Prof. Challis had entered upon an examination of 

 this subject soon after the publication of Sir David Brewster's expe- 

 riments ; these he had repeated and verified in most points. He had, 

 however, found that when he varied the inclination of the piece of 

 retarding glass to the rays of light, the lines varied considerably. — 

 Sir D. Brewster had examined the phenomena under every inclina- 

 tion of the piece of retarding glass, having varied it through all angles, 

 both in a vertical direction and also horizontally, and had noted and 

 described the effect produced upon these lines. — The Astronomer 

 Royal admitted the difficulty of reducing such complex phenomena 

 under the dominion of mathematical expression, but as far as the 



