362 Proceedings of Societies. 



prevent a normal eye from distinguishing the accompanying colour from 

 the blackness or whiteness which tends to extinguish it. 



If this be the case (and Mr Maxwell's method and apparatus would 

 serve admirably for testing the truth of the belief), then a colour- 

 blind eye is not a normal eye in all but the perception of red, nor can 

 colour-blindness be properly defined as " anerythric or no-red vision." 

 A colour-blind eye is, I apprehend, abnormal, in its perception of certain 

 at least of the tints and shades of all colours, and this so far justifies the 

 phrenological hypothesis of a diminution of the entire organ of Colour (if 

 there be such an organ at all) in the colour-blind, and is to myself one 

 of the strongest justifications of the use of the word colour-blindness, 

 which, however, is of Sir David Brewster's coining, not of mine. 



3. The question why green should be mistaken for red remains still a 

 puzzle, but 1 cannot enter into the discussion of this question at present. 

 I hope to bring it before the Society again. 



4. Mr C. Maxwell's spectacles for the colour-blind introduce a new and 

 important feature into the construction of optical aids for their defects. 

 In the many previous proposals to use coloured glasses, the colour-blind 

 person had no means of deciding what colour of glass he was at the mo- 

 ment using, and might fancy himself looking through a red glass when 

 he was using a green. 



But by placing red in one eye of the spectacles, and green in the other, 

 and making it simply a question which, used singly, renders a colour 

 known to be either red or green brighter, the decision of the true nature 

 of the colour resolves itself into brightness under right eye, versus bright- 

 ness under left eye, supposing the spectacles to be made, as they general- 

 ly are in England, so as to bridge the nose only in one way. The foreign 

 double-bridged spectacles would defeat the end in view. 



5. In conclusion, I would, through you, beg Mr Maxwell not to con- 

 fine himself to sharply defined cases of colour-blindness, but to extend his 

 beautiful method of inquiry to the less attractive but more common cases 

 of uncertainty as to all colours, which we may anticipate he will also 

 bring under law. 



Observations on Mr Maxwell* s Paper. By Professor J. D. Forbes. 



I do not know whether 3 r ou advert at all to the history of experiments 

 on the mixing of colours, but I may mention that I find by my register, 

 that my chief experiments were made on the 4th and 12th January 1849 ; 

 and amongst these results I find "yellow 100°, blue 120°, white 140°, 

 produce a quite neutral gray like black 180°, white 180°." " Yellow 

 and blue only, equal, produce a yellow grey or citrine — never green." 

 [The yellow was gamboge.] 



On the 1st March 1849, I have the following entry : " Examining the 

 red, yellow, and blue papers by the colours they reflect in a dark room, 

 when a narrow slip of each was strongly illuminated by the sun, and the 

 light examined (not in the plane of reflection) by a prism, the colours 

 appear very complex indeed. Both the red and yellow reflect almost 

 every colour of the spectrum. The blue seems purest, but very decidedly 

 violet or tinged with red. 



2. Notice of the Occurrence of British newer Pliocene Shells in the Arctic 

 He is and of Tertiary Plants in Greenland. In a letter from Dr 

 Scoular of Dublin. Communicated by James Smith, Esq., of Jordan- 

 hill. 



Dr Scoular to Mr Smith. 

 "I have lately had the opportunity of examining a series of fossils from 



high Arctic latitudes, brought home by Captain M'Lintock, R.N. The 



