J. LeConte on some phenomena of Binocular Vision. 35 



nose was not in the way) its fellow on the other side of the 

 nose. In other words, in binocular vision when the eyes are 

 fixed upon a distant object the whole field of view, including the 

 parts of the face, is shifted by the right eye one half the inter- 

 ocular space to the left, and by the left eye the same distance to 

 the right, without altering the relative position of parts. By 

 this shifting it is evident that the two eyes with tneir visual 

 lines are brought in perfect coincidence, so that identical points 

 in the two eyes are perfectly united. 



The outline of the field of view varies somewhat with the 

 prominence of the nose, brows and cheek bones, but its general 

 form is much the same in all persons. I give in the accom- 

 panying figure (fig. 6) a rude outline of the field of view in my 

 own case, nn rr being the field of the right eye, and n'n'll the 

 field of the left eye, and the irregular space nn n'n' being the 

 common field of binocular vision bounded by tlie outline of the 

 nose nn as seen by the right eye, and n'n' as seen by the left eye. 

 The circle E represents the position of the combined eyes in 

 the center of the common field, I and r' the position of the two 

 eyes as seen each by the other or rather as they seem each to the 

 other. A vertical projection is shown .j 



in fig. 7. E being the combined eyes 

 a and n' the nose as seen by the righ 

 and left eyes respectively on cither sid( 

 of the common field, and I r' eacli eye a 

 seen by the other. It will 1 

 that I have represented the eye on the extreme right by r' instead 

 of r, and on the extreme hfi by / instead of V. The reason is 

 that these, like the two noses, are only heteronymous ma^es seen 

 by the two eyes respectively from their central position. As an 

 <*rgan of vision the two eyes occupy the central position only, 

 but as an object each from this central position sees its fellow on 

 the other side of the nose right and left. This vertical projection 

 I shall use in all my diagrams representing double images. By 

 its use, however, we may represent equally well the position of 

 objects or images seen' single at the point of sight. By this 

 method the visual results of even the most complicated figures, 

 not only may be represented truly and with ease. l)ut iruiy be 

 worked out a priori with the utmost certainty. The great im- 

 portance of this a priori help will be appreciated by all who 

 have made experiments in binocular vision, and who therefore 

 know how easy it is to overlook, or rather how diflficnlt it is 

 often to perceive, many of our visual impressions. 



As we have alreadv" stated, while we gaze at a distant horizon 

 any object in the median line ivhatever he its distance is seen 

 double, the space between the imaires being exactly equal to the 

 mterocular si)aec. Evidentlv then the median line of sight 



