SCIENTIFIC SUMMARY. 
249 
MICROSCOPY. 
The Illumination of Opaque Objects under High Powers . — In our last 
number we described the ingenious invention of Mr. Smith, of Kenyon 
College, U.S., which has been adopted with slight modification by Messrs. 
Powel & Lealand. We have now to describe a method, based upon a 
similar principle to Mr. Smith’s, which has been devised by Mr. Dancer, of 
Manchester. Instead of placing the mirror immediately over the opening at the 
back of the object-glass, a small speculum, B, one-sixth of an inch in diameter, 
is introduced into the front, C, of the body of the microscope, 2| inches above the 
top of the objective. A lateral opening, D, is made in the body at right angles 
to the speculum for the admission of light, to be reflected down through the 
objective to the object below it. The interposition of this 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, good 
definition may be obtained by Mr. Dancer’s method when the speculum 
employed is of the proper curvature. The contrivance can always remain 
attached to the microscope without interfering with the general appearance 
of the instrument, and when the use of the speculum is not required, it can 
be withdrawn or turned aside out of the field of view, and the aperture at the 
side of the body may be closed by a small shutter. The new contrivance 
can be adapted to both binocular and uniocular microscopes. Another 
method consists in placing a concave mirror, at at A, so as to reflect light 
down through the prism of the microscope, and upon the object. We must 
VOL. V. — NO. XIX. S 
