152 AXXUAL OF SCIENTIFIC DISCOVERY. 



the middle of the right compartment, and it will seem as at first to belong 

 ri|ii;illy to both eyes. 1 



Referring to the results observed in the above experiments, when the 

 object is directly in 1'ront of either eye, it may be concluded that the mere 

 inal impression on cither eye is unaccompanied by any consciousness of 

 the special Mirihce impressed; and that the formation of the visual percep- 

 ti..ii appertains to that part of the optical apparatus near or within the brain, 

 which belongs in common to both eyes. 



These observations show moreover that the perceived direction is just as 

 truly normal to the central part of the retina which has received no light, as 

 to tiiat of the retina on which the white spot has been painted. Indeed, as 

 before indicated, it is normal to neither, but is felt to be in the middle line 

 between the two; that is, in the binocular direction. It need scarcely be 

 added, that this conclusion is at variance with the law of visible direction, 

 maintained by Brewster, which requires that the apparent direction of an 

 object shall in all cases be normal to the part of the retina impressed. 



The reference of .the object, in certain cases above noticed (parts of 1, 2, 

 and 4), to one eye chiefly, and that the eye from which it is actually hidden, is 

 accounted for by the direction in which the other eye receives the light. As 

 this direction, in the case of the left eye, for instance, would be decidedly 

 toward the field of view of the right eye, it would at once suggest the place of 

 the object as somewhere before that eye; and so, when the object is actually 

 before the right eye, but in a position towards the left, it would excite the 

 idea of an object somewhere before the left eye. As the retinal picture alone 

 gives no indication of the particular eye in which it is formed, but only ex- 

 cites a visual consciousness common to both, the object in these cases will 

 seem to be visible by both eyes, but chiefly by that before which the sugges- 

 tion just mentioned would naturally place it. 



Exp. 5. Thus if we place on the black slide of the stereoscope two spots, 

 differing either in shape or color, one before each eye, we perceive them both 

 in the middle or binocular direction, each seemingly visible in an equal de- 

 gree to both eyes, the one being seen through or upon the other, according 

 to the fitful attention or suggestion of the moment. A pleasing modifica- 

 tion of this experiment is made by using two unequal white spots on the 

 black slide, and interposing a green or other colored glass between one of 

 them and the lens. The spot which appears colored will give as strongly the 

 impression of being seen by both eyes as the white one, in spite of our 

 knowledge of the position of the colored glass. 



Exp. 6. To observe this effect satisfactorily, it is well to make the experi- 

 ment in an apartment in which a single small lamp is placed at some distance 

 from the spot on which we stand. Looking intently at the lamp, we bring 

 the pencil before the face in such position as to give us an image on each 

 side of the lamp, and then move the pencil toward the right until its left 

 hand image seems to coincide in direction and position with the lamp, which 

 appears to shine through, or to partially replace it. As we continue to look 

 thus at the lamp, we have a clear impression that both lamp and pencil are 

 equally visible to both eyes; and without some consideration of the previous 



l The effect here described is one of a series of phenomena, which Dr. O. W. 

 Holmes attribute to an actual transfer of impressions from one eye to the other, 

 and which he proposes to explain by the hypothesis of reflex vision. 



