236 WRITINGS OP JOSEPH HENRY. [18*5 



thing else besides the form and position in the leaves and 

 fruit of a cherry tree, perceived b}'' his playmates but not seen 

 by himself. Two of his brothers had the same imperfection, 

 while two other brothers, his sisters, and other relatives, had 

 the usual condition of vision. 



Of the other class the cases are much more numerous; we 

 shall however give onl)?^ a few examples. Mr. Harvey, of 

 Plymouth, mentions a tailor who could see in the rainbow 

 but two tints, namely, yellow and bright blue. Black ap- 

 peared to him in general — green, sometimes crimson ; light 

 blue appeared like dark blue, crimson, or black; green was 

 confounded with black and brown ; carmine, red, lake, and 

 crimson, — with blue. 



But the most interesting case of this kind is that of the 

 celebrated chemical philosopher, Dr. Dalton, of England. 

 He published an account of his own case and that of several 

 others in the Transactions of the Manchester Society, in 

 1794. Of the seven colors of the rainbow he could distin- 

 guish but two, yellow and blue ; or at most, three, yellow, 

 blue, and purple. He saw no difference between red and 

 green ; so that he thought the color of a laurel leaf the same 

 as that of a stick of red sealing wax. A stor}'' is told of his 

 having, on one occasion, appeared at the Quaker meeting, of 

 which he was a member, in the usual drab coat and small- 

 clothes of the sect, with a pair of flaming red-colored stock 

 ings to match. Whatever maybe the truth in reference to this 

 story, we have the assertion of Professor Whewell, that when 

 Dr. Dalton was asked with what he would compare the scarlet 

 gown with which he had been invested by the universit}', he 

 pointed to the trees, and declared that he perceived no dif- 

 ference between the color of his robe and that of their foli- 

 age. Dr. Dalton found nearly twenty persons possessed of 

 the same peculiarity of vision as himself; and among the 

 number the celebrated metaphysician, Dugald Stewart, who 

 could not distinguish a crimson fruit, like the Siberian crab- 

 apple, from the leaves of the tree on which it grew otherwise 

 than by the difference in its form. 



On account of the prominence conferred on this defect of 

 vision by Mr. Dalton's publication, the continental philoso- 



