64 Scientific Proceedings, Royal Dublin Society. 
is used by the observer to trace the image seen on the ground-glass 
stage ; and, asstated, pencil-point, scale, the image of the pupillary 
disc, and the projected shadow of the opacities in the eye are all 
seen in the same plane with perfect clearness. Hence, if the head 
and eye are kept steady, the drawing or tracing is made with ease 
even by an unskilled observer. The only difficulty consists in the 
contraction and an apparent dilatation of the pupil; the former 
occurs even in uniform light during accommodation, when the 
attention is concentrated in the act of drawing. ‘This difficulty, 
however, is overcome by keeping the eye fixed for a few moments 
on the pencil-point before the tracing is made, or by dilating the 
pupil artificially when a careful drawing is required. The latter, 
a curious elusive dilatation, I will return to presently (see § 8). 
After the drawing has been made the ground glass can be removed, 
and a photographic print taken, which is kept for comparison 
with the tracing made by the observer at a subsequent time. 
In my own case, so minute and clear are the shadows of the 
darkened tissues of the crystalline lens, that I can detect the 
slightest change, noting the gradual extension of the opacity, and 
could watch week by week the effect of any remedy if such were 
known. 
For convenience of observation, in a later form of the 
apparatus, shown in fig. 2, Plate III., I have hinged the vertical 
pillar P, so that the observer, when using the instrument, may 
incline it to suit himself; a single pillar is used in order to leave 
the hand free to draw on the ground-glass stage G', which carries 
a supporting hand-rest &. The eye-pieces HE have shaped cups 
to fit the eye and bring the cornea within a definite distance of the 
pin-hole. In this way the pin-hole can be placed at the anterior 
focus of the eye (about half an inch from the cornea), for the reason 
already explained in Part I.; and the stage is placed at a fixed 
distance so as to give a definite magnification. 
It is important in using the Entoptiscope that the observer 
should be comfortably seated and completely at ease; he should 
have his hands free and not be troubled to keep one eye closed; it 
is much better in fact to keep both eyes open. ‘This is done in 
using either of the instruments shown on Plate III.; in the 
smaller one the shaped sliding head-rest keeps all light from 
