462 POPULAE SCIENCE EE VIEW. 
liand hitlierto free^ and places it in front of the examined eye, 
and at such a distance as to make the focus of the lens coin- 
cide with the pupil of that eye — a distance varying from two 
to three inches. He himself will usually need to be at a 
distance from twelve to eighteen inches. This is for normal 
eyes. The slight movements backward and forward necessary 
to adjust these distances correctly, are effected very easily and 
precisely after practice ; but at first it is a little difficult to 
avoid changing the direction of the mirror while thus slightly 
advancing or retiring the head ; and this is a point on which 
it is well to give a warning, for it is a frequent source of dis- 
couragement to beginners, who find that at every movement 
they interfere with the illumination of the eye, and so suffer 
from a series of little failures at the outset. The first thing, 
in fact, that every one sees, amounts to little more than a red 
luminous disc ; those who begin by seeing nothing more, 
therefore, need not to be discouraged ; a little patience and 
time will enable them to see what more practised persons 
describe. The eye to be examined may be more fully observed 
by dilating the pupil with atropine — a drop of a solution, one- 
grain to a pint of water, or one of the atropised gelatines pre- 
pared for me by Savory and Moore, each of which contains 
one hundred thousandth of a grain of atropine, and will 
