£32 Mr Blackwall on a New Species of Lamprotorrris. 



nel will lose their pre-eminence when put in competition with an 

 invention which enables others to make discoveries. 



Note D. — It does not appear, I think, that Fresnel had made 

 any distinct supposition as to whether the two rays in the axis 

 should be considered as the ordinary and extraordinary ray in 

 their ultimate state, or not. From all that I could extract from 

 his Memoirs, I was always in doubt whether both the ordinary 

 and the extraordinary ray in the neighbourhood of the axis 

 ought not to be considered as divided each into two circularly 

 polarized rays. 



Note E. — It is proper to mention that I had exhibited this 

 phenomenon to the Cambridge Philosophical Society in the 

 spring of last year, long before the publication of Dr Brewster's 

 valuable Memoir in the Phil. Trans, for 1830, and (I believe, 

 but I do not recollect the date,) before its communication to the 

 Royal Society. 



Note F. — This may be considered as the definition of right- 

 handedness of the crystal : and this observation gives the readi- 

 est means, with a thin plate, of determining whether it is right- 

 handed or left-handed. If the plate be thick, the easiest me- 

 thod is to observe in which direction the analyzing plate must 

 be turned to make the rings dilate. 



Observatory, Cambridge, 

 Dec. 30, 1830. 



Art. XXI. — Description of a new Species of Lamprotornis. 

 By John Blackwall, F. L. S., &c. Communicated by the 

 Author. 



There have been recently deposited in the Museum of the So- 

 ciety for the promotion of Natural History established in Man- 

 chester, two specimens of a bird belonging to the genus Lam- 

 protornis, which, notwithstanding it is one of the most superb 

 species of its tribe hitherto discovered, appears to have escaped 

 the notice of ornithologists. The following description will 

 serve to convey some idea, though it must be admitted a very 

 inadequate one, of this highly interesting and beautiful bird : 



