1. Dr» Brewster*s Memoirs^ 363 



II. Foreign. 



1. Dr. Brewster's Memoirs. 



We have received from Dr. Brewster of Edinburgh, the 

 following Memoirs, which he had obligingly forwarded to 

 us, previously to their publication in Europe. We should 

 have noticed them in our last number, had not ill health 

 prevented. (Ed.) 



1. Description of a monochromatic Lamp, for microscopical 

 purposes, ^c, (Trans. R. S. Ed.) — This lamp is construct- 

 ed, so as to produce a homogeneous flame by the combus- 

 tion of diluted alcohol, which burns with a light almost 

 purely yellow, and the very few green and blue rays ac- 

 companying it, may be intercepted by a plate of the palest 

 yellow glabs. The lamp may be used with or without a 

 wick. The best wick is a piece of sponge, and the volume 

 of yellow flame may be greatly increased by covering it 

 with a frame of wire gauze so adapted that it may be pres* 

 sed upon the sponge when red hot. If a permanently 

 strong light is required, the alcohol should be burned with- 

 out a wick in a dish of platinum, heated by a spirit lamp 

 beneath it. The light of this lamp gives a perfect distinct- 

 ness to microscopic objects, and removes^ all the errors 

 arising from the different refrangibility of light. 



Annexed to this description, are, a number of remarks 

 on the following points relating to the absorption of pris- 

 matic colours. — 1. The manner in which coloured media 

 absorb the different portions of the prismatic spectrum. — 

 2, The influence of heat in modifying this absorbent pow- 

 er — and 3, the determination of the question, whether or 

 not yellow light has a separate and independent existence 

 in the solar rays. This Dr. B. decides in the affirmative, 

 and moreover that the prism is incapable of decomposing 

 that part of the spectrum which it occupies. 



2. Additional observations on the connection between the 

 primitive forms of minerals and the number of their axes of 

 double refraction. — This is a continuation of a former pa- 

 per on the same subject. Since the publication of the 

 former paper the objections to his principle have been re- 



