56 
The Presidents Address. 
Smitli^ of Kenyon College, Ohio^ U. S.^ described a new con- 
denser he had devised for the opaque illumination of objects 
under high powers. It has long been felt that it would be 
immensely to the advantage of microscopic anatomy if such 
small bodies as the blood- globules could be viewed as opaque 
objects with high powers. Hitherto there have been great 
and insurmountable difficulties in the way, but Professor 
Smith has at length contrived an illumination which promises 
to effect good service. 
In this instrument a pencil of light is admitted above the 
objective and thrown down through it on the object, by 
means of a small silver mirror placed on one side, and cutting 
off a portion of the aperture. Professor Smith sent an 
instrument of this kind to Mr. Lobb, with a request that he 
would place it in the hands of Messrs. Powell and Lealand. 
These gentlemen devised what they considered to be an im- 
provement, and substituted for the small silver mirror, to 
which Professor Smith had given a preference, a flat glass 
placed at an angle of 45°, across a tube interposed like an 
adapter between the objective and the microscopic body. A 
pencil of light entering by a side aperture striking against 
this flat glass is partly reflected down through the objective 
and on to the object, the magnified image of which is viewed 
through the glass. 
If the flat grass is ground so as to have parallel surfaces, no 
noticeable error is introduced even with the highest powers. 
About the same time, or a little later, that Messrs. Powell 
and Lealand were thus at work, Mr. Richard Beck devised a 
similar arrangement ; but he employed a circular disc, such as 
used for covering microscopic objects, instead of the more 
solid glass of Messrs. Powell and Lealand. 
At the December meeting of the Society Mr. Beck ex- 
hibited his new mode of illuminating opaque objects under the 
highest powers. It consisted of a disc of thin covering glass 
set at an angle of about 45° in the optic axis of the micro- 
scope. This was placed close behind the setting of the object- 
glass in a special adapter, having a suitable aperture for ad- 
mitting light from a lamp, the rays from which were reflected 
downwards. The object-glass thus served for its own achro- 
matic condenser. The definition of the object is not injured 
by the transmission of rays through the thin glasts. 
The idea of employing the object-glass as its own condenser 
was suggested by Mr. Hewitt upwards of five years ago. In 
consequence of his communication Mr. Wenham was induced 
to give the plan a trial. A concave speculum was fitted at an 
angle into the body of the microscope, having a central hole 
