SEVENTEENTH ANNUAL MEETING. 95 



water enveloped in oil boiled at ISO , and the different temperatures at which steam 

 condensed in different oils (in my experiments) would seem to indicate, must be deter- 

 mined by further and more exhaustive research. 

 University of Kansas, November 26, 1884. 



STATISTICS ON COLOR-BLINDNESS IN THE UNIVERSITY OF KANSAS. 



EDWARD L. NICHOLS, PH. D. 

 [Abstract.! 



During the past two years I have tested the members of my classes in physics for 

 color-blindness with the Holmgren worsteds. The primary object in these tests was the 

 practical illustration of this interesting subject in the class-room, but the statistics thus 

 collected have some features which may be of more general interest. 



The most noteworthy of these is the unusual prevalence of "incomplete" green- 

 blindness among our students. From the far more extended series of tests already made 

 in Europe,* and elsewhere in this country,! it has been ascertained: that among men 

 about 4 per cent, are completely color-blind; that "red" and "green" blindness are 

 about equally prevalent; and that with very few exceptions women are not color-blind. 



The results of my tests were in accordance with those made elsewhere, so far as the 

 above-mentioned particulars are concerned. Of 137 young men subjected to the Holm- 

 gren test, five were found to be completely red-blind and four completely green-blind. 

 Of 93 young women, one was completely red-blind. The percentage of those completely 

 color-blind, ( 6.56 per cent for males,) while above the average, is not in excess of the 

 percentages frequently obtained by other experimenters. ( Dr. Feris, for instance, found 

 in testing 501 French sailors that 8.18 per cent, of them were color-blind. Dr. Dor, who 

 tested 611 women in Breslau, found 0.82 per cent, of them to be color-blind.) The nuni 

 ber of cases in which the perception of green was notably deficient — in other words, the 

 amount of incomplete green-blindness — was, however, surprisingly large. Besides the 

 four persons classed as completely green-blind, no less than eighteen were found to be 

 incompletely green-blind; so that, including the former, more than 16 per cent, of all 

 the males tested were pronouncedly green-blind. Of the usually more prevalent type, 

 ( red-blindness,) but four cases were detected. The total amount of red-blindness was 

 therefore less than 6 per cent. Among the female students, on the other hand, but two 

 cases of green-blindness were found, and in both the deficiency was very slight; while 

 four cases of incomplete red-blindness were recorded. 



Even this great excess of green-blindness over the other common variety is not un- 

 precedented. Dr. Krohn, who tested 1,200 railroad employes in Finland, found the 

 ratio of green-blindness to red-blindness to be even larger — i. e., 25: 4. More com- 

 monly, however, the latter is the prevailing type; to the extent in Favre's tests upon 

 French railways, for instance, of 13: 1. 



The great ditlerences exhibited in color-blind tests, in different parts of the world, 

 are doubtless to a considerable extent due to the different methods pursued, and in the 

 earlier investigations, to the very imperfect knowledge of the subject possessed by those 



*Foran account of the principal European investigations prior to 1877, see F. Holmgren; Dc la 

 Cedle des Oouleurs dansses rapports dvec les Cht mins-de*fer et in Marin* , Stockholm, is77. (Translated in 

 Smithsonian Reports for L877.) 



fSee B. Joy Jefferies' work (Color-blindness and its Detection, Boston). 

 7 



