XII. 
ON ENTOPTIC VISION. 
Part LY. 
By W. F. BARRETT, F.R.S., 
Professor of Experimental Physics, Royal College of Science for Ireland. 
CONTENTS. 
PAGE PAGE 
1. Haipincer’s Turts, : . 112 ) 3. Tas Puncrum Cacum 
or Buinp Spor, ; a er 
2. Tue Macuria LuTEa 4, PurKINIJE’S FicuREs, i 5 | eet 
or YELLOW Spor 5 . 119 | 5. Movine Corpuscuzs, é e293, 
(Puates VI.—VIII.) 
[Read, Apriz 24; Received for Publication, Junz 22; Published, Ocr. 29, 1906.] 
Tue sense of sight is intended and adapted for the perception of 
the external world; hence the training of the organ of vision from 
infancy onwards has rendered it an exquisite instrument for the 
detection and localization of visible phenomena in the world out- 
side ourselves. But the retina receives impressions from objects 
within as well as from without the eye; these impressions we have 
learnt to disregard, and hence do not perceive them unless they 
are novel and insistent. But even faint, unheeded retinal im- 
pressions from a source within the eye can usually be perceived if 
they are sought for. The perception of those phenomena the seat 
of which is within the eye may be called Entoptic vision; and the 
perception of phenomena the seat of which is outside the eye may 
be termed ordinary or Ezoptic vision. 
In two previous communications which I have recently made 
to the Society, I have described certain entoptic phenomena, con- 
sisting of shadows cast on the retina by minute obscurities within 
the eye, which are perceived when a luminous point is near the eye. 
SCIENT. PROC. R.D.S., VOL. XI., NO. XII. Q 
