60 Transactions of the Royal Microscopical Society. 
icith a small aperture a spherical refractive particle exhibits a 
dark even jet black terminal annulus. If a body be studded with 
such beading it will necessarily appear dark from an assemblage 
of shadows ; when the definition is exalted, these beads considered 
as lenses exhibit in general too small a central point of illumination 
to be detected in ordinary glasses. Even if perfectly refracting 
and unembarrassed with other substrata, beads so small as the 
thirty-thousandth of an inch form an image of a radiant source 
of light inconceivably minute. 1 ”* “ Supposing the glasses free 
from annular aberration, greater depth of vision with black out- 
lines is given by a reduced aperture with direct light On 
the other hand, enlarged aperture appears to illuminate a dark 
object, if transparent; it converts apparently, in many cases, 
opacity into translucence, transforms a reddish-brown scale into a 
brilliant object, reveals interstitial sparkling, and developes new but 
often delusive appearances in eidolic forms.” 
* “ 1 The image of a brilliant flame is in all such cases swelled out by the 
imperfection of the glasses into an exaggerated spurious disk.” 
