

$. P. Lathrop on. Single and Double Vision. 345 



very easily discovered that the same law was followed in the 

 order of their appearance. The appearances from three pieces of 

 paper were the following — commencing with "natural single 

 vision/' and numbered in the order of the degree of convergence. 

 The images that are doubled are placed nearer each other than the 

 others; No. 1. q q d— No. 2. D D D D— No. 3. q d qq d , 

 or D D D D D according as the attention, or the eye, is turned 



12 3 4 5 6 



more particularly to the right or left. No. 4. D □ D D D D 



1 2 3,4 5 6 



No. 5. d Q □ □ □ — where the images 3 and 4, separate in No. 4, 



l 2 3,4 5,6 1,2 3,4 5 6 



are here made to coalesce. No. 6. DDDO, orOOOO, 

 according as the attention is given to the right or left. No. 7. 



*' 2 3,4 5,6 1.2 4 3 5,6 



D □ D — where we have three images again. No. 8. D D D D 

 where the images 3 and 4 have been made to pass each 



1,2 4 3 6 5 



other while the other remains united. No. 9. D D D D D, or 



2 1 4 3 5,6 



□ ODD D — according as the attention is given to the right 



2 14 3 6 5 



or left. No. 10. D D D D D D — where each of the images of 

 the several pairs have been made to pass its fellow, and six im- 

 ages again appear, lam nearly able to lap the images marked 

 1 and 4, and those marked 3 and 6, as in the case with two pieces 



2 1, 4 3, 6 5 



of paper, as follows: No. 11. D □DOD D. By continuing to 

 increase the degree of convergence these images can be made to 

 coalesce, so that there will again be only three images, thus: 



2 ' 4 l6 3 > 5 • ' 1 • XT . 



□ D D, and even to assume a position reverse to that in No. 4, 



654321 j • , • r . 



thus : DDDDDD; as was said m the instance of two pieces 



of paper. 



Under the head of "some of the phenomena of the illusive 

 image/' Dr. Locke observes, — "as the head is inclined to the 

 right or left, the superimposed pictures slide out from each other, 

 the one ascending and the other descending to the extent of the 

 inclination." I found, when using two pieces, with a converg- 

 ence of the optical axes sufficient to produce three images, that 

 if the head be then inclined to the right shoulder at an angle of 

 45°, there would then appear four images in the following po- 



sition • ft gj . By permitting the convergence to diminish 



gradually, the images marked 1' and 2' would be seen to move 

 along the dotted lines and finally coalesce with the images 1 and 



Second Sebies, Vol. VII, No. 21.— May, 1849. 44 



