MEMORANDA, 149 
with which the light requires to be directed to avoid the end 
of the object-glass causes too much loss by reflection from 
the surface of the cover, and the use of the Lieberkthn then 
becomes indispensable. Now, if we cover up a portion of the 
reflecting surface of the Lieberkiihn, we shall be enabled to 
obtain any proportion of oblique light in one particular 
direction, and then, by rotating the Lieberkiihn upon the object- 
glass, may bring it to bear upon every part successively, 
without having to alter the position of the object. In this 
way the most delicate structure—such as the barbs upon the 
very beautiful and nearly transparent spinesof Opuntiaiunicata, 
which are scarcely to be detected by the whole light—may be 
brought owt into full and bold relief. The elegant arrange- 
ments assumed by crystallized silver can scarcely be seen to 
advantage in any other way, and the exquisitely beautiful and 
varying forms which are brought out by the changing play ot 
light so obtained give it somewhat the appearance and charm 
of a moving panorama of dazzling whiteness. The plan I have 
adopted is to fix a triangular piece of thin, dull-black paper 
upon the silver with gum, and, when dry, to trim off the 
projecting parts from the centre and circumference with a 
sharp penknife, so as to give it a neat appearance. ‘The tube 
of the Lieberkiihn should move freely upon the object-glass, 
and be provided with a milled ring, so as to be easily rotated 
between the finger and thumb. In the absence of the ring a 
few coils of narrow tape, or a strip of paper fixed with gum, 
will be found to answer the purpose sufficiently well—W. 
Kerncety Bripceman, Norwich. 
A Simple Object-Finder for Students’ Microscopes.—During 
the last year I have been using a simple addition to the stage 
of my microscope, which acts as a most efficient object-finder. 
I find it most accurate with all powers up to the {-inch 
object-glass. 
The diagram shows the arrangement, and represents the 
stage of a student’s microscope as made by Smith and Beck. 
In order to use this finder with a microscope, it is necessary 
for the object-carrier to be well fitted, and move easily and 
accurately in the vertical direction. The object-carriers of 
all good students’ microscopes are, I believe sufficiently well 
fitted, and I find that of Messrs. Smith and Beck answers 
perfectly. 
The finding line (a) is a fine, black, engraved line marked 
on the stage of the microscope, near its right margin, 
vertical to the object-carrier, and parallel to its plane of 
