45p Prof. Locke on the. Phantascope, 



Exp. 5. Let there be a horizontal heavy line placed to the 

 left and a vertical one to the right on the base-board, thus : 

 — I , then adjust the screen and superimpose the images 

 to form a phantom. That phantom will be a cross, and the 

 whole will appear thus : — +1 



Exp. 6. Do the same with any other parts of a figure of 

 which one shall be the complement of the other; the phantom 

 will be the complete figure. Thus, take the picture of a person, 

 cut it out of the paper, and cutting off' the head, place the 

 body on one side of the base-board and the head upon the 

 other ; the converged phantom will be the complete figure, 

 the head coming in from one side and the body from the other. 

 It is perhaps unnecessary to say, that each part must be 

 placed in its true elevation, thougli displaced horizontally. It 

 was in repeating this experiment that I discovered that my 

 eyes did not appear to be mates ; for I saw the body clearly, 

 but the head obscurely. After a little time, however, these 

 conditions interchanged, and I saw the head clearly and the 

 body obscurely. Nor did I seem to have any voluntary con- 

 trol over these conditions, but my eyes continued to relieve 

 guard according to some rule of their own. This is rather an 

 amusing experiment. The figure being beheaded, the phan- 

 tom ghost appears between the two parts of the body ; and 

 from a little unsteadiness of the optical convergence, the 

 ghost's head is inclined to attitudinize, and will sometimes 

 start off" a little from the body, and in returning will go a little 

 too far, and will break the neck in the opposite direction. If 

 the head of the experimeter be a little inclined, then the head 

 of the phantom will come on too high or too low. 



Exp. 7. I placed a card, having two perpendicular parallel 

 lines, about two inches in length and three inches apart. On 

 converging them in an attempt at superposition, I found the 

 converged lines were not parallel, but came in contact at the 

 upper end first, and diverged a little downward. Standing 

 with my head erect, I repeated this experiment by converging 

 voluntarily, and without the aid of any index, the parallel 

 sides of a window ; the same want of parallelism was exhibited ; 

 but on throwing my head backward and looking horizontally 

 over my cheeks, the converged perpendiculars coincided 

 throughout. I learned by this that both of my eyes do not 

 rotate in one and the same horizontal plane. 1 got another 

 person to repeat the same experiment ; and he found the error 

 of his eyes to be in the opposite direction, the converged per- 

 pendiculars meeting first at the bottoms. This proves a moral 

 adage to be physically true, " we don't all see alike." 



This instrument, and the researches into binocular vision, ' 



