Royal Societt/, ' 22I 



the globe, and showing at one view the territorial extent, 

 the military strength, and the commercial importance of 

 each state. 



Dr. Brewster, of Edinburgh, is about to publish a Trea- 

 tise on new Philosophical Instruments for various purposes 

 in the Arts and Sciences, with Experiments on Light and 

 Colours, in one volume 8vo. with twelve Plates. 



Mr, Thomas Forster has now in the press Meteorological 

 Researches and Journals, with Engravings, 8vo. 



XXXV. Proceedings of Learned Societies, 



ROYAL SOCIETV. 



In our report of last month, our account of Dr. Brewster's 

 paper was in some respects inaccurate; the following is 

 more correct : 



This paper contained a short abstract of Dr. Brewster's 

 numerous experiments on light and colours, and was divided 

 into ff)ur parts. 1. On a new property impressed upon 

 light by transmission tlirough the ajate. When lio-ht is 

 transmitted through a thin plate of transparent no-ate cut 

 in a direction perpendicular to the laminre, Dr. Brewster 

 has found that it possesses all the characters of one of the 

 pencils formed by double refraction, one of the inia'^c of the 

 lummous object from which it proceeds disappearino- in 

 every quadrant of its circular motion when viewed by a 

 prism of Iceland spar. The kindred substances of carneiian 

 and chalcedony possess the same property. 2, On the 

 double refraction of chromate of lead. Dr. Brewster found 

 that this metallic salt possessed a double refraction, which 

 was nearly ihrire as great as that of Iceland crystal. 3. On 

 substances which have a greater refractive power than the 

 diamond. Since the time of Sir Isaac Newton, who first 

 discovered the powerful action of the diamond upon lieht 

 it has always been conceived that this precious stone pos- 

 sessed the highest refractive pow er of all bodies whatever ; 

 but Dr. Brewster has found that both chromate of lead 

 and realgar exceed it considerably in refractive power, 

 4. On a double dispersive power in doubly refractiuo cry- 

 stals. Dr. iirewster has discovered, that all bodies that 

 possess a double refraction have also a double dispersive 

 power, one of which is very much greater than the other- 

 Mic highest dispersive power of Iceland spar being consi- 

 derably 



