Mr. B. S. Proctor on the Focal Adjustment of the Eye, 299 

 Table of Adjusting Powers. 







Vertical. 



Horizontal. 



Right eye. 



Two eyes. 



Right eye. 



Two eyes. 





•{ 



r> 



10 



20 



30 



10 



20 



30 



10 



20 



30 



10 



20 



30 



B. S. P. . 



w 



14 



14 



23 



14 



17 



23 



10 



15 



27 



10 



15 



20 



T. P. B. . 



•{ 

 i 



D 

 W 



D 



9 



18 











9 



18 



... 



11 



5 



22 

 12 



33 

 21 



F. S 



W 



12 



22 



... 





... 





9 



20 











M.J. P.. 



••{ 



D 



8 



16 



24 



8 



16 



24 



8 



16 



24 



8 



16 



24 



W 



H 



n 



m 



5 



n 



m 



3 



7 



12 



H 



n 



11 





••{ 



D 



6 



12 



18 



6 



12 



18 



6 



12 



18 



6 



12 



18 



F. R 



W 



6i 



10 



13 



5 



8 



11 



5 



10 



16 



6 



10 



M* 



W. W. P. 



••{ 



W 



7 

 6 



14 

 10 





7 

 6 



14 

 10 





7 

 5 



14 

 9 





7 

 5 



14 

 10 





M. S 



••{ 



D 



11 



22 



33 



11 



22 



33 



11 



22 



33 



11 



22 



33 



W 



10 



20 



20 



10 



20 



20 



10 



20 



20 



10 



20 



20 



Note — The lines marked D give the distance in inches at which observations 

 were made, any convenient short focus being taken for comparison with the results 

 obtained at twice and three times the distance. 



The lines marked W indicate the resolving power in thousandths of an inch 

 according to the principle made use of in the last Table. 



In examining the results indicated in these Tables, there must 

 necessarily be some allowance made for the impracticability of 

 deciding exactly when the object is in its best focus. Few observers 

 could indicate their focal distance with decision to within a quarter 

 of an inch ; consequently when there is only a fraction of an 

 inch between the foci of the eyes, or between the foci for the 

 vertical and horizontal lines, that may be disregarded, unless the 

 same fraction recurs in parallel experiments. 



Of nine observers, seven have the same focus for both eyes. 

 In one case the focus for the right eye is longest, and in one that 

 for the left is longest. 



Four have a longer focus for vertical lines. Two have a 

 shorter focus for vertical lines. Three have equal foci for both. 



Of seven observers, six have the power of varying the focus 

 for both horizontal and vertical lines, and one for the horizontal 

 line only. All have the power of bringing both lines into focus 

 at once at distances beyond the shortest focus, particulars of 

 which are as follows : — 



B. S. P. sees both horizontal and vertical lines clearly at the 

 same time at 9 inches distance with the left eye or both eyes, 

 and at greater distances with the right eye. 



T. P. B. with the right eye sees both lines clearly at 30 inches ; 



