344 S. P. Lathrop on Single qnd Double Vision. 



In performing the second and third experiments, I found, in 

 addition to what is mentioned by Dr. Locke, by a still greater 

 degree of convergence of the optical axes, other results of an in- 

 teresting character. The second experiment is the following: 

 Two candles of equal size and height were placed side by side 

 on a table, and, by converging the axes of the eyes, four images 

 were produced. As the convergence progressed, each pair of 

 images receded gradually from the original place of the single 

 image until the two contiguous ones — the second and third, ap- 

 proached, and finally coalesced into one, when three images only 

 were in view. This he illustrates in the following manner, using 

 letters, in the place of which I have substituted squares, repre- 

 senting the pieces of paper which I employed in performing 

 the experiments. These were laid upon a dark colored spread, 



12 12 3 4 



Thus: No. 1. D D — Natural single vision. No. 2. D D D D 



1 2,3 4 



•View with axes slightly converged. No. 3. D D D — View 

 with greater convergence of the optical axes and the two inter- 

 mediate images coalesced into one. By a still greater converg- 

 ence, I have found that the second and third images— now coal- 

 esced — can be made to pass by each other, when four images 



13 2 4 



will again be seen, as follows ; No. 4. D D D D. As the con- 

 vergence commences, these intermediate images are seen to re- 

 cede from the place of the original images, when four images are 

 seen, as in No. 2 ; then to approach one another and coalesce, 

 when three images only appear, as in No. 3 : then to pass by 

 each other, when four images are again seen. By a yet greater 

 convergence I am able to cause the image marked 3, in No. 4, to 

 lap upon the image marked 1 ; and the image marked 2, to lap 



13 2 4 



upon the image marked 4, as follows : QU CD . From which 

 I infer, that by a still greater convergence, these images can be 

 made not only to coalesce — when two images only would be 

 seen — but to pass by each other, when four images would again 



3 14 2 



appear in the following position : D D D D, and so on, till the 

 images marked 1 and 4 coalesced and passed by each other, and 

 even till all the four images had changed their relative position 



4 3 2 1 



and assumed the following D D D Q , — that is, the reverse of the 



order in No. 2. 



periment 



pe 



only modifications being those which would arise from the greater 



number of images. W 



preserve the images distinct, or to bring them all in view, but 



