CHAPTER V. 
THE CONDENSER: ITS FITTINGS AND 
ITS USE. 
VT ENT in importance to the objective among our 
^ optical appliances comes the condenser. The 
paralleliser or bull’s-eye is sometimes called a con¬ 
denser, and is sometimes used really as a condenser, 
but throughout this book, when the term “ condenser ” 
is used, it is to be taken to mean the “ substage con¬ 
denser.” 
It is to be noted that, without a good condenser, the 
good qualities of the best objectives are lost ; the 
function of the condenser being to furnish a cone of 
rays of such angular compass as could not be obtained 
without some condensing arrangement, and such as 
is appropriate to the angular aperture of the objective 
used. It will be found that in all cases the angle of the 
cone projected by the condenser ought to bear some 
fairly close relation to the aperture of the objective in 
use. If we use a cone of large angle with an objective 
of low angle we shall destroy the performance of the 
latter ; and if we use an objective at a large aperture 
with a condenser of low aperture, we simply throw away 
the most valuable quality of the objective. 
