W. B. Rogers on Retinal Impressions. 405 
eves be converged to some point nearer than the end of the tube 
the circular image will appear against the side of the tube giving 
Let the observer next direct his view toa very remote object, 
as the sky, seen through the window, still retaining the previous 
adjustment of the tubes. He will now see two circles, continu- 
ing separate as long as he keeps his eyes fixed’on the distant 
surface ; and if the finger be held up as before in front of one 
of the tubes it will appear within the circle which is in front of 
the other eye; thus causing the impression on the right eye to be 
apparently transposed to the left, and vice versa. 
xp. 4. Fasten a small dise of white paper on a slip of black 
pasteboard of the size suitable for a stereoscope, and place this 
in the instrument so that the white spot shall be centrally in 
front of one of the glasses. of al 
rson not aware of the position of the spot it will appear 
in the stereoscope as if equally in view to both eyes and he will 
entirely unable to decide on which retina its picture is impressed. 
Indeed properly considered the spot does not appear directly in 
front of ya eye but is seen at the intersection of the optic 
axes, in the medial or binocular direction between the two. 
