332 WB. Rogers on Binocular Vision. 
: > . ene 
‘ject of which ‘I. have seen any description.* “The best way,” 
e says,. “to make this experiment is toetake two lines AB ad, 
(fig. 41,) of unequal léhgths, and with a large pin to perforate 
Revit Di Ggpme figs: oA 
- ‘ 
A a 6 
the lines at AB ab so that when we attempt to unite them we 
shall see with perfect distinctness their four luminous extremi- 
ties. When‘the point a is made to pass into A, I have never suc- 
ceeded in making 6 pass into B. Whenever there is an appearance 
, Of this either turn round the paper or the head so as to separate the 
ines and it will be invariably seen that if a springs out of A, 6 will 
think more satisfactory explanation of the optical coincidence of — 
the unequal lines. Drawing the two lines in very opaque ink on 
somewhat thin letter paper, of the lengths of one inch and eight- 
tenths of an inch respectively, with perforations at the ends, I 
place the paper at the distance of distinct vision between the eyes 
bright window or the globe of a solar lamp, and by the 
usual binocular effort bring the two lines together—either behind 
or in front of their true place. — - 
At first, if the axial movement be slow, I see the two lumin- 
ous ends of the shorter line vibrating on the longer one, and if 
bring aand A to coincide I see 6 and B separated, or making the 
axes meet in front of the paper, 6 and B are united at a greater 
distance than a and A, and hence the resultant recedes towards 
the right, 
ahs do Se 
