J. LeConte—Phenomena of Binocular Vision. 1938 
instruments. This then is the purpose of this structure. Jt 
gives periscopism to the eye. 
uch is a brief statement of Dr. Hermann’s discovery, and 
his deductions therefrom. This discovery I regard as very 
great accuracy the exact degree of indistinctness. This is an exam- 
ple of one kind of indistinctness of vision. But if I hold my 
pen far to one side, on the extreme verge of the field of view, 
Say 90° from the direction of the optic axis, the pen is again 
indistinct, far more so than before, but from an entirely differ- 
ent cause, viz: imperfect perception of the retinal image. My 
perception, in fact, is so imperfect that I cannot tell whether 
the image is distinct or not. This is an example of the other 
kind of indistinctness of vision. 
ow of these two kinds of indistinctness, the latter is by far 
the greater. Objects on the margin of the field of view are 
} 
* Loc. cit. 
