Hastings — Optical Constants of the Human Eye. 209 



illuminated by sunlight, through a prismatic ocular and find 

 the displacement of the globule when sharp definition of the 

 spectrum was secured at different Fraunhofer lines. These 

 observations are by no means easy, but they were carried out 

 with remarkable skill so that the means of four series gave, 

 after eliminating the dispersion due to the lens of the ocular, a 

 result of exactly the same degree of precision as my own. 

 Professor Wolf made no other use of his results than to prove 

 that the human eye has notably greater dispersion than the 

 reduced eye of Listing which is supposed to be made of pure 

 water ; but a reduction of them after the method in which 

 mine were treated, when corrected for the slight degree of 

 hvpermetropy possessed by his eye, gave 6n '/^ n equal to 1*523. 



In view of this fact I should prefer 1-54 as a definitive value 

 were so small a change really worth while. Since the last 

 value only differs from that employed by an amount equal to 

 the probable error attaching to it, we may, I think, accept the 

 results given above with considerable confidence. 



Yale University, January, 1905. 



