230 



Prof. Rogers thought that the physiology of vision was 

 as yet but imperfectly understood ; vision by correspond- 

 ing points of the two retinae, for instance, cannot be 

 maintained, though it is found in all treatises on physi- 

 ology, and in most on optics. 



Dr. Gould referred to the fact that though in strabis- 

 mus there is distinct vision with the normal eye, the 

 other being unused, squint-eyed persons cannot get the 

 stereoscopic solid image, but only see a flat picture. 



• 



Prof. Rogers remarked that there is such a thing as 

 being right-eyed and left-eyed, as well as right-handed 

 and left-handed ; indeed many persons use but one eye 

 for taking their direction in vision, and that is generally 

 the right ; it is sometimes the left, but in normal in- 

 stances an object is seen in the median plane between 

 the two eyes. Many persons have the idea that stereo- 

 scopic vision is only squinting, but this is very far from 

 being the case; in squinting, the eyes converge to a 

 point nearer than that of distinct vision ; in stereoscopic 

 vision the eyes are not so directed, and the sense of 

 fatigue and discomfort is owing to the forcible dissocia- 

 tion of two naturally associated actions. In common 

 vision there are two adjustments, one consisting in direct- 

 ing the optic axes to the object, the other in adjusting 

 them to suit the distance of the object from the eyes, 

 drawing them, so to speak, out or in like the joints of a 

 telescope ; habit enables us to elTect these two adjust- 

 ments instantaneously and at the same time. In looking 

 through a stereoscope, while the object is very near, we 

 are forced to extend our optic tubes to see an object 

 apparently at a great distance, and thus the union of the 

 associated motions is violently broken up, causing a 

 sense of fatigue. 



The Corresponding Secretary read the following let- 

 ters, viz : — 



