17 



retina has become fatigued and surcharged with the two images by- 

 long attention. The principal attention being directed to p, its limb 

 will appear to pass over that of m; whilst an equal attention to both 

 will cause them to intersect like two translucent disks. This double 

 intersection is not apparent when one of the bodies is very small, the 

 light of the larger being suffused over the smaller, which, moreover, 

 does not present sufficient area to allow the intersection of so small a 

 portion of the larger limb to be observed. When the apparent dia- 

 meter of p is not greater than that of the coexisting limbs, as when 

 the experiment is performed with a small pin's head and a silver coin, 

 it is evident that the greater part, if not the whole of the image, may 

 coalesce with that of m upon the retina, producing the phenomenon 

 in question. 



I wish this experiment to be verified by other eyes than my own, 

 especially as it has only succeeded with my near-sighted eye, at 

 arm's length, during day-light. At about six feet distance, by lamp- 

 light, and with two dimes, my son could not distinguish which one 

 passed over the other; or rather he believed that the moving body 

 (p) passed in front; but I did not allow more than one-tenth inch of 

 intersection. A single person might perform the experiment by 

 placing the disks upon one end of a strip of board, and so adjusting 

 them, that by the motion of the board, the one should appear to the 

 eye stationed at the other end, to pasfe over the other. 



Pending nominations, from No. 203 to 223, inclusive, and 

 new nomination, 224, were read. 



Prof. Frazer, Reporter, laid upon the table No. 39, Vol. IV. 

 of the Proceedings of the Society. 



Stated Meeting, April 21. 



Present, thirty-five members. 



Dr. Patterson, Vice-President, in the Chair. 



Letters were received and read: — 



From the New York Historical Society, dated New York, 

 9th April, 1848, transmitting the Proceedings of the Society, 

 VOL. V, — c 



