1845] WRITINGS OF JOSEPH HENRY. 235 



will be perceived which passes in succession through all the 

 colors of the rainbow. 



Of the real cause of these appearances we are as yet almost 

 entirely ignorant. Professor Plateau, of Ghent, has indeed 

 referred them all to a few simple principles; but these appear 

 to us rather expressions of the law of succession of the phe- 

 nomena, than physical explanations of them. We do not 

 however at this time intend to dwell on this class of phe- 

 nomena, but to give a succinct account of those peculiarities 

 of vision, in which abnormal perceptions of color are perma- 

 nent, and which are fully treated of in the memoirs, the 

 titles of which stand at the head of this article. 



The peculiarity of vision called color-blindness, and some- 

 times Daltonism, may generally be referred to two classes. 1. 

 Those in which all impression of color, except white and 

 black, are wanting. 2. Those in which the individual can 

 perceive certain simple colors, but is not able properly to 

 distinguish between them. There are persons, strange as it 

 may appear, in whom the sense of primary color is entirely 

 deficient, and who, in place of red, yellow, and blue, see 

 nothing but different degrees of white and black. Professor 

 Wartmann gives a number of cases of this kind. The most 

 ancient of those he finds described is that by Dr. Tuber- 

 ville, in 1G84, of a woman about 32 years of age, who 

 came to consult the Dr. about her sight, which though ex- 

 cellent in other respects, gave her no impression in reference 

 to color, except white and black. Spurzheim mentions a 

 family, all the members of which could distinguish only dif- 

 ferent shades of white and black. An account is given by 

 Mr. Huddart of a shoemaker, in Cumberland, who could 

 distinguish in different colors only a greater or less intensity 

 of light, calling all bright tints white and all dull ones black. 

 Plis peculiarity of vision was unknown to him until one day, 

 while a boy, playing in the street, he found a stocking, and 

 for the first time was struck with the fact that it was called 

 by his companions red, whereas to his mind it was capable 

 of no farther description than that designated by the word 

 stocking ; he was thus led to conclude that there was some- 



