E L. Nichols — Sensitiveness of the Eye to Colors. 39 



matic light lessened until its effect was lost to the eye, would 

 certainly be better; but ease and rapidity of execution were 

 essential where so many individuals were to be tested and 

 where the time of those who kindly presented themselves for 

 the purpose was limited. Moreover, the study of spectral 

 tints would not give results directly applicable to pigments, 

 and it is the latter with which we have to do in many practical 

 problems in the science of chromatics. An exhaustive study 

 ,of this subject would involve the use of both methods. 



Table I gives the general results of the fifty-four tests. The 

 averages for males and for females are given separately for 

 purpose of comparison. The numbers indicate in each case 

 the amount of coloring matter present in one hundred million 

 volumes of white, in the most dilute mixture which can be 

 distinguished from a pure white by the average observer. 



Table I. 



Number of parts of coloring matter that must be mixed with 100,000,000 parts of 

 white in order to affect the tint of the compound. 



Chromate Chromic 



Red lead. 01 lead. oxide. Ultramarine 



Average for 31 males 15-9 17-3 817-7 148-5 



Average for 23 females 59-8 33-2 913-6 108-1 



Average for both sexes 25-2 23-9 864-2 126-5 



The popular impression that in woman the special senses are 

 more finely organized and delicate than in man,* a view con- 

 siderably strengthened so far as color-perception is concerned 

 by her well authenticated exemption from color-blindness, 

 finds no support from these experiments. As will be seen 

 from the above table the average male observer is measurably 

 more sensitive to red, yellow and green, while the female 

 shows superiority in the blue alone. Quite as interesting, 

 perhaps, is the manner in which the relative sensitiveness of 

 the eye varies with the wave-length. If the corresponding 

 data for mixtures of white and monochromatic light were 

 obtainable it would be possible to indicate by curves the vari- 

 ations of the sensitiveness of the eye in this particular. The 

 light reflected by pigments, however, is so far from being 

 monochromaticf that it is out of the question to attempt to 

 assign them any place in a pure spectrum, and curves con- 

 structed upon the assumption that pigments are representative 

 of definite wave-lengths would be of interest only as illustrat- 

 ing in a very imperfect way the general character of the curves 

 which might be obtained by a more precise method. 



* Some experiments upon the sense of smell, carried on at the same time as 

 and partly in connection with the tests described in the present paper, indicate 

 that in the case of many common odors also, delicacy of perception is much 

 more marked among men than among women. (E. H. S. Bailey: Proceedings of 

 the Kansas Acad, of Sciences, 1884.) 



t See "A spectro-photometric study of pigments," American Journal of Science, 

 vol. xxviii, Nov., 1884. 



