lloyal Society. 



an arch, when they are well defined, its span along the hori- 

 zon, its height above it, or its place among the stars, will be 

 valuable for comparison. At all stations the time at which 

 the light passes to the south of the zenith should if possible 

 be stated, as well as the precise times of very brilliant or 

 active displays, which frequently last but a few minutes. 

 Lastly, it should be noted how much beyond the zenith, to 

 the south, the bands of light descend. The degree of bril- 

 liancy may be denoted by the terms — faint, moderate, bright, 

 very bright. 



LX. Proceedings of Learned Societies, 



ROYAL SOCIETY. 

 [Continued from p. 141.] 

 Jan. 10, T?XPERIMENTS and Observations upon the Properties 

 18.50. J-^ of Light." By Lord Brougham, F.ll.S. &c. 

 The author states that the optical inquiries of which he hero 

 gives an account were conducted in the first instance under the most 

 favourable circumstances, arising from the climate of Provence, 

 where they were commenced, being peculiarly adapted to such 

 studies : he further states that he subsequently had the great benefit 

 of a most excellent set of instruments made by M. Soleil of Paris ; 

 remarking, however, that this delicate apparatus is only required 

 for experiments of a kind to depend uy)on nice measurements, and 

 that all the principles which he has to note in this paper as the 

 result of his experiments can be made with the most simple appa- 

 ratus and without any difficulty or expense. His statement of the 

 results of his experiments is thrown into the form of definitions 

 and pro;)Ositions, for the purpose of making it shorter and more 

 distinct, and of subjecting his doctrines to a fuller scrutiny. He 

 premises that he purposely avoids all arguments and suggestions 

 upon the two rival theories, the Newtonian or Atomic, and the Un- 

 dulatory. 



The following are the author's Definitions ani Propositions. 



Definitions. 



1. Flexion is the bending of the rays of light out of their course 

 in passing near bodies. 



2. Flexion is of two kinds — infiexion, or the bending towards the 

 body ; deflexioji, or the bending from the body. 



3. Flexibility, defiexihility, inflexibility express the disposition of 

 the homogeneous or colour-making rays to be bent, deflected, 

 inflected by bodies near which they pass. 



Proposition L 

 The flexion of any pencil or beam, whether of white or of homo- 

 geneous light, is in some constant proportion to the breadth of the 



