Tue Microscope. 157 
similar to that gathered at St. Joseph, we are forced to believe 
them both to have the same origin. 
I have a number of slides of snow sediment and will will- 
ingly exchange them for other mounts. 
H. W. Westover, M. D. 
St. JoSEPH, Mo. 
BECK’S VERTICAL ILLUMINATOR AND IMMERSION 
OBJECTIVES. 
BY. A. Y. MOORE, 
HERE is no piece of accessory apparatus better adapted to 
bring out the qualities of our better class of homogeneous 
immersion objectives than Beck’s (or some analogous form of) 
Vertical Illuminator. Its principle is simple enough: <A short 
tube screws between the nose of the body and the objective. 
In one side of this tube is a hole—generally about a quarter of 
an inch in diameter—to admit a beam of light upon a piece of 
thin glass placed diagonally in the tube and so mounted that a 
rotating movement can be given to it. When the light strikes 
this piece of glass it is reflected downwards, into the back lens 
of the objective, and after successive refractions is brought to a 
focus upon the object. Thus it will be seen that the objective is 
its own achromatic condenser, and as the quality of the con- 
denser is the same as that of the objective, a condensation of 
light takes place which is far superior to that given by the best 
substage condensers made; for the majority of substage con- 
densers, although they may be of exceedingly wide aperture, 
are not corrected for chromatism and sphericity to the extent re- 
quired in first class objectives. Upon the side of the short tube, 
which contains the thin glass reflector—that is the mounting of 
the Verticle Illuminator, is generally placed some kind of dia- 
phragm forthe purpose of regulating the amount of light admit- 
ted to the glass reflector and to confine that whichis admitted to 
certain parts of the glass surface. For if the light be admitted 
in a narrow beam only, on to the central part of the reflector and 
