INSENSIBILITY OF THE EYE TO COLOURS. 281 



intellectual. Its immediate function is to give us the sensation of light 

 and colour. In this it cannot be supplied by any of the other senses. 

 The action is, therefore, the result of organization ; or is a " law of 

 the constitution;" requires no education; but is exercised as soon as 

 the organ has acquired the proper developement. Yet, occasionally, 

 we meet with cases, in which the eye appears to be totally insensible 

 to certain colours, although capable of performing the most delicate 

 functions of vision. Sir David Brewster 1 has collected several of these 

 cases from various sources. A shoemaker of the name of Harris, at 

 Allonby, in Cumberland, could only distinguish black and white; and 

 whilst a child, could not discriminate the cherries on a tree from the 

 leaves, except by their shape and size. Two of his brothers were almost 

 equally defective. One of them constantly mistook orange for grass 

 green, and light green for yellow. A Mr. Scott, who describes his own 

 case, 2 mistook pink for pale blue, and full red for full green. His 

 father, his maternal uncle, one of his sisters, and her two sons, had the 

 same defect. A Mr. R. Tucker, son of Dr. Tucker, of Ashburton, 

 mistakes orange for green, like one of the Harrises ; and cannot dis- 

 tinguish blue from pink, but almost always knows yellow. He mistakes 

 red for brown, orange for green, and indigo and violet for purple. A 

 tailor at Plymouth, whose case is described by Mr. Harvey, 3 of Ply- 

 mouth, regarded the solar spectrum as consisting only of yellow and 

 light blue;, and he could distinguish, with certainty, only yellow, white 

 and gray. He regarded indigo and Prussian blue as black; and purple 

 as a modification of blue. G-reen puzzled him exceedingly; the darker 

 kinds appearing to him brown, and the lighter kinds a pale orange. 

 On one occasion, he repaired an article of dress with crimson instead 

 of black silk ; and on another occasion patched the elbow of a blue 

 coat with a piece of crimson cloth. A still more striking case is given 

 by Dr. Nicholls 4 of a person in the British navy, who purchased a blue 

 uniform coat and waistcoat, with red breeches to match. Sir David 

 Brewster refers to a case that fell under his own observation, where 

 the gentleman saw only the yellow and blue colours of the spectrum. 

 This defect was experienced by Mr. Dugald Stewart, 5 who was unable 

 to perceive any difference between the colour of the scarlet fruit of the 

 Siberian crab and that of its leaves. Dr. Dalton, 6 the chemist and 

 philosopher, after whom the defect has been most unjustifiably termed 

 daltonism, could not distinguish blue from pink by daylight ; and in 

 the solar spectrum, the red was scarcely visible ; the rest of it appear- 

 ing to consist of two colours, yellow and blue. Mr. Troughton, the 

 optician, was fully capable of appreciating only blue and yellow; and 

 when he named colours, the terms blue and yellow corresponded to the 

 more or less refrangible rays : all those that belong to the former, 

 exciting the sensation of blueness ; and those that belong to the latter 

 that of yellowness. Dr. Hays, 7 who has collected the history of nume- 



1 Optics, edit, cit; Letters on Natural Magic; and art. Optics, in Library of Useful Know- 

 ledge. 



2 Philos. Trans, for 1778. 3 Edinb. Phil. Transact., x. 253. 

 4 Medico-Chirurgical Trans., vii. 477, ix. 359. 



6 Elements of the Philosophy of the Human Mind, ch. iii. 



6 Manchester Memoirs, v. 28. 



7 Proceedings of the American Philosophical Society for August 21, 1840. 



