THE 



AMERICAN JOURNAL OF SCIENCE 



[FOURTH SERIES.] 



Art. XI Y. — On the Optical Constants of the Human Eye 

 for different Colors ; by Charles S. Hastings. 



A complete determination of the optical constants of the 

 human eye for all conditions of accommodation and for all 

 colors is yet wanting in the literature of physiological optics. 

 Indeed, the only addition to the knowledge possessed by 

 Helmholtz and published in his famous Physiologische Optik 

 nearly forty years ago, consists in a slight change in his assump- 

 tions as to the dimensions of the schematic eye and a calcula- 

 tion of its cardinal points when accommodated for a near 

 object.* 



A necessary use for a larger knowledge recalled to my mind 

 a series of observations made several years ago for a different 

 purpose, but which would clearly yield the required informa- 

 tion. These observations are contained in the following table, 

 in which the first column contains the Fraunhofer line which 

 defines the kind of light observed ; the columns headed N" and 

 F, respectively, the nearest and farthest distances, in inches, at 

 which I could see distinctly the spectral line ; the column 

 under — e is the mean of the reciprocals of N" and F, and the 

 last column the difference of these reciprocals. 



jine 



N 



1/N 



F 



1/F 



— c 



1/A 



A 



15-75 



•06349 



18:00 



•05556 



•05952 



•00793 



D 



12*60 



'07937 



13-80 



•07246 



•07592 



•00691 



F 



10-40 



•09615 



11-25 



•08889 



•09252 



•00726 



G 



8-60 



•11628 



9-50 



•10526 



•11072 



•01102 



I.K 



7-25 



•13793 



8-50 



•11765 



•12779 



[•02028] 



* It should be noted that W. Einthoven computed the constants for two 

 different ref rangibilities, namely, for that of the Fraunhofer D and F lines, 

 for a schematic eye adjusted for great distance ; but his assumption that the 

 dispersive power is very nearly as great as that of dense flint glass makes 

 them unavailable. A possible missprint renders two of the constants erro- 

 neous. See Pfliiger Archiv. f. Physiol., lxii, 166. 



Am. Jour. Sci.— Fourth Series, Vol. XIX, No. 111. — March, 1905. 



14 



