90 W. B. Rogers on Binocular Vision. 
ee ee nS 
steadily on the resultant, we see the two other images take their 
places beside it in the same plane and of the same magnitude as — 
its principal section if it represent a solid. 
In making this experiment, it is best to use identical figures, 
such as two equal bodies about an inch in diameter whose centres 
are 14 inches apart. If, while the three figures are thus visible 
in the same plane, the eyes be suffered to glance sideways for a 
moment, the component figures retreat or advance from the plane 
of the resultant, and a renewed effort is necessary to bring them 
back to it. At first some difficulty is experienced in retaining 
comes easy, at will, to shift the components into or from the plane 
of the resulta at the same time to observe the change of — 
their apparent magnitude Bee 
presents itself in the case of the two im- 
us as the pencil. 
in the latter the glo 
sition. 
