300 W. LeConte Stevens—Notes on Physiological Optics. 
and E respectively. When the card is revolved, as in fig. 4, 
the distance O E exceeds OD, and hence the visual angle sub- 
tended by EG is less than that subtended b . ver 
ellipse therefore is distorted. ‘To each eye separately the effect 
is the same as if every major axis were bent, and every pomt 
of each curve were correspondingly displaced; F and G’ are 
elevated, F’ and G depressed, and hence F and F” differ in ret: 
nal latitude as well as longitude. The binocular combination, 
however, is perfect, although double images due to difference 
in retinal latitude are neither homonymous nor heteronymous. 
That conjugate points differing slightly in altitude can be bi- 
nocularly viewed and their images combined, even when there 
is no horizontal stereoscopic displacement, was first shown by 
Professor W. B. Rogers.” is is one of several considerations 
which show that the theory of corresponding points in binocu- 
