72 J. LeConte on Binocular Vision. 
raise the finger until its images fall upon figures separated from 
one another by an intervening figure and then look steadily at 
the finger. The other planes may be obtained in a similar 
manner. The position of the several planes may be also easily 
calculated ; the data being the inter-ocular line, the distance of 
the object and the interval from center to center of the figures. 
Both by measurement and calculation I determined the planes 
in the case of the carpet to be 21-5, 13:05, 9:37 and 7:3 inches 
coe = the case of the oil-cloth they were 11°8, 6°54 
and 4°5 in 
If the Sistiies between the centers of contiguous figures be 
less than the inter-ocular line, then still other images may be 
seen beyond the real object and very much enlarged. The po- 
sition of the eyes and the place of the image in this case also 
3. 
+ Ly 2 
is s easily explained. If dabec oe 3) be the plane of the real 
object, and the eyes I and II be directed toward contiguous” 
figures a _ b but not crossed, then the image of a and 6 will — 
con and be seen at a’ the “intersection of the visual lines. 
So also a and d will be seen at d' and 6 and c atc’, and oo 
0 represent the position of the image jane. In 
Ostler to: ae es maaan we aes ust gaze iota soe beyond 
the = until we obse the d ouble images come together — 
and , and then fix the ao steadily. The enlar ee 
Te eealy becomes distinct, . 
GF ak 
reey 
a 
fl 
ee 
if 
Fly 
i 
iiey aet. eee pee ag = 
pest with pertect eae ee papering I had = 
