140 YEAK-BOOK. OF FACTS. 



While .able perfectly to distinguish between red and green, the con- 

 trast does not readily catch his eye, especially at a distance ; in fact, 

 he is somewhat short-sighted in respect to these colours. He has 

 reason to believe that, in his case, there has been a gradual im- 

 provement in his actual perception of colours, independently of his 

 greater knowledge of them ; though this is in opposition to the general 

 experience of those whose vision is in any way abnormal, and no 

 other instance was known to. the late Professor George Wilson, 

 whose book is the standard one on the subject of colour-blindness.* 



THEORY OF COLOURS. 



In the Philosophical Transactions has appeared a paper by Pro- 

 fessor J. Clerk Maxwell, of King's College, on the Theory of Com- 

 pound Colours, and the Relations of the Colours of the Spectrum. 

 The professor gives, first, a history of the theory, with especial re- 

 ference to the researches of Newton, Young, Brewster, Grassman, 

 and Helmholtz : an account of his own experiments follows, witli a 

 reduction of his observations. He gives as the results the following 

 among other general conclusions : — The three primary colours in the 

 spectrum are red, green, and blue ; by the mixture of these, colours 

 chromatically identical with the other colours of the spectrum may 

 be produced — the orange and yellow are equivalent to mixtures of 

 red and green, which seems to put an end to the pretension of yellow 

 to be considered a primary colour ; and the extreme ends of the 

 spectrum (very feeble) are probably equal to mixtures of red and 

 blue. 



At a meeting of the French Academy of Sciences, during a conver- 

 sation respecting the optical phenomena of the eclipse of July 18, 

 M.( hevreul referred to the remarkable phenomena of Complementary 

 Colours, and stated that he was then printing in the Society's 

 Memoirs an account of his latest researches. 



CRYSTALLIZATION AND POLARIZATION' IX DECOMPOSED GLASS. 



SlB 1 ». Bbewstbb has communicated to the British Association a 

 ' ' Notice respecting certain Phenomena of Crystallization and Polarisa- 

 tion in Decomposed Glass." At the meeting of the Association held 

 in Aberdeen, the anther read a paper on the Decomposed Glass found 

 at Nineveh, Rome, and other localities ;f but not then having any 

 drawings to e\hil>it to the section, he found it difficult to convey an 

 igible account of die structure and remarkable phenomena 

 which the specimens exhibited both in common and polarised light. 

 I [e now exhibited and explained very beautifully-execub d coloured 

 drawings and diagrams explanatory "t tins.- appearances and pro- 

 perties. In this paper he omitted all reference to those colourless 

 specimens by which be had then shown that a bundle or pile of these 

 transparent films act upon oommon and polarised light as negative 

 nniaxal crystals, producing all the oolonrs of polarized light, by the 

 interference of two oppositely polarised pencil . one of which is tho 



• See rear-Book of Fact; 1860, p. ISO. t Md. p. US. 



