202 



E. S. Ferry — Persistence of Vision. 



of botany and iinds no great inconvenience in any of his 

 studies except chemistry. This subject he was obliged to dis- 

 continue as he could not distinguish the characteristic colors 

 of the reactions. His neutral point was sharply located at 

 •516 /. This gentleman wore glasses for near-sightedness. 

















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V30 vso V70 v?0 5/0 530 550 570 590 CIO . £30 t50 £70 190 



Duration of Impression for different colors of red-blind Eye. 



The other observers were not aware of any similar cases in 

 their families. The neutral point of Mr. G. A. W. was located 

 at -517;,; Mr. W. M. at -5165 *; Mr. L. M. W. at -518 k; 

 Mr. H. C. H. at -516 L They are all green-blind and their 

 eyes appear to be otherwise perfect with the exception of 

 Mr. "W. M., who is near-sighted. Their values of duration of 

 impression are given in the annexed table. 



The values of Mr. W. C. W. are platted in the full curve 

 fig. 3 ; the broken curve being the curve of the normal eye 

 for the same brightness of spectrum. The values obtained by 

 Messrs. W. M., EL C. EL, and L. M. W. are platted in the 



