Mr. B. S. Proctor oh the Faced Adjustment of the Eye. 297 



three times the distance. In all these experiments, the person 

 whose sight was being examined did not know the measurements 

 till the conclusion of the experiments ■ thus was avoided any ten- 

 dency which there might have been to fancy that at double the 

 distance double the width of the lines was requisite to admit of 

 resolution. 



The adjustment of the eye is only partly under command of 

 the will, but the power over it increases with practice, various 

 observers being able to obtain a focus with facility at the end of 

 a few experiments which was not readily obtained at the com- 

 mencement ; they also gain a facility in deciding when the test- 

 object is in perfect focus, or the best attainable focus. 



While some have hesitated long before deciding, others have 

 come to a definite and fixed conclusion at once, and on repeat- 

 ing the experiments, have given the same results, although they 

 had not the means of knowing that the distance or size which they 

 required the second time was the same as they selected the first. 



The following Tables give the results of an analysis of the 

 sight of nine individuals : — 



Table of Shortest Foci. 







Vertical line. 



Horizontal line. 



Note. 



Inches. 



Inches. 



B. S.P., J 

 age 33. | 



T. P. B., r 



age 44. j 



F. S., j 

 age 19. | 



J. D., J 

 age 43. ] 



C. B., J 

 age 36. ] 



M.J. P., f 

 age 35. 1 



F. R., J 

 age 19. | 



W. W. P., r 



age 26. 1 



M. S., 

 age 47. 



Right eye. 

 Left eye. 

 Both eyes. 



Right eye. 

 Left eye. 

 Both eyes. 



Right eye. 

 Left eye. 

 Both eyes. 



Right eye. 

 Left eye. 

 Both eyes. 



Right eye. 

 Left eye. 

 Both eyes. 



Right eye. 

 Left eye. 

 Both eyes. 



Right eye. 

 Left eye. 

 Both eyes. 



Right eye. 

 Left eye. 

 Both eyes. 



Right eve. 

 Left eye. 

 Both eyes. 



n 



6i 



12 

 11 

 11 



4 



n 



7 



m 

 lot 



8 

 8 

 9 



H 



5 

 5 



H 



n 



6 

 5f * 



H 



n 



H 



4 



4 



8 

 8 

 8 



HI 



1H 

 ill 



8| 

 8 



8* 

 4i 



H 



H 



5 

 5 

 5 



•i 



H 



H 



The observers, with 

 two exceptions 

 (F.S.andM.J.P.), 

 were accustomed 

 to the use of the 

 microscope, the 

 telescope, or both ; 

 andonlyone(M.S.) 

 was in the habitual 

 use of spectacles. 

 The distances in- 

 dicated are the 

 shortest at which 

 thelines were seen 

 in clear focus. 

 Some observers 

 could not retain 

 these short foci 

 for more than a 

 few r seconds. 



