92 W. B. Rogers on Binocular Vision. 
more remote than S. But in this case the union is easily effected — 
by directing the eyes past m to a point in the wall or other distant — 
object in the room, and approaching or receding until a — ; 
convergence is attained. After a little practice even this becomes — 
unnecessary, as we can then at will direct the eyes as if gazing 
upon objects at various distances behind S 
In this mode of combination, the picture of the object. proper 
to the right eye 1s viewed by that eye and - picture proper 10 
the left eye by the left, just as with the common stereoscopes. 
Hence the drawings intended for the eter instruments may be 
used in this, provided they are so close to one another as to bring 
the points which are to be united, nearer together than the cen- _ 
tres of the eyes. The ordinary twin-figures on black paper can 
to very easy catuhiiation by. dividing the paper trans- 
versely so as to separate the figures and then placing them on the 
. the greatest distance om A at which a double drawing on the 
r can be used, but it be moved up nearly to r with- — 
pi disturbing the paper, as in’ th -interva the strip is cut away 
to anarrow stem. When separate dra eae employed ee : 
may be moved with the stage to any desired nb 
Band A. 
intersection in common. ‘This, which is a peculiar adaptability 
of the present instrument, leads as we shall hereafter see, to some _ 
curious stereoscopic effects 
en we propose to form the resultant figure somewhere be- 
tween the drawings and our eyes, it is necessary to place the twit 
picture or the separate drawings on the stage D, and to adjust the. 
to such a position that looking through the opening m™ 
with the right eye we see only the left hand drawing, and look- 
ing with the left eye we see only the oe hand drawing. yy 
both eyes be then directed toward the o ing, we observe in Of — 
 * it, hanging in the air, the beautifully clear binocular re- — 
suit 
The resultant figures thus formed has a relief just the reverse — 
of what it would be with the same drawings placed on the upper 
stage of the instrument, for in the present instance the right ey 
views the drawing proper to the left eye, and the left that proper" 
to the right. Hence by simply shifting the paper from one slag@ 
