182 PROCEEDINGS OF SOCIETIES. 
A concave mirror or lenticular prism can also be used for the 
same purpose, provided the focal length is adapted to the length 
of the body and object-glasses. 
Various modifications can be adapted so as to vary the character 
of the illumination to suit the particular object to be viewed. In 
some cases the Wenham’s prism may be withdrawn a little, to 
produce the proper effect. 
Uncovered objects only can be seen to advantage, owing to the 
light reflected from the surface of the covering glass. The surface 
on which the objects are mounted should reflect as little as pos- 
sible, and be a marked contrast in colour to the object. 
Ordinary Meeting, November 28th, 1865. 
R. Anaus Surru, Ph.D., F.R.S., &c., President, in the Chair. 
Mr. Francis Hampson, solicitor, was elected an Ordinary 
Member of the Society. 
Mr. Dancer, F.R.-A.S., said that in a paper “ On the Illumina- 
of Opaque Objects under the High Powers of the Microscope,” 
read before the Microscopical Section of this Society, November 
20th, he had described a method of employing the oblique body of 
the binocular microscope with Wenham’s prism, for illumination 
of opaque objects, and he had also exhibited an instrument fitted 
up for this purpose, giving the members present a practical 
demonstration of the advantages which this mode of illumination 
afforded under certain circumstances. He wished now to describe 
another method of illuminating opaque objects, and, as it is equally 
applicable to monocular and binocular microscopes, it appears 
worthy of some consideration. 
In the method of Mr. H. L. Smith, of Kenyon College (which 
was briefly described in the paper beforé mentioned), and also in 
the use of the Wenham’s prism, there is a considerable loss of 
angular aperture (which is a very important consideration). It 
occurred to the author that by modifymg Mr. Smith’s contrivance 
this loss might be diminished in some degree; this has been 
attempted in the following manner. 
Instead of placing the mirror immediately over the opening 
at the back of the object-glass, a small speculum }th of an inch in 
diameter is introduced into the front of the body of the micro- 
scope, 24 inches above the top of the objective. A lateral opening 
is made in the body at right angles to the speculum, for the admis- 
sion of light to be reflected down through the objective to the 
object below. 
The interposition of the small speculum does not produce any 
disagreeable effect in the field of view, and in the examination of 
objects it is easy to use that portion of the field which is between 
the centre and the edge. With proper manipulation very good 
