248 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
objective. The following are some of tbe valuable features of this 
arrangement : — 
It allows the entire angular aperture of all objectives to be used, 
which is not the case when using the Nicol's analyser and large-angle 
low-power objectives. The stage can be kept in a horizontal position 
in chemical experiments and in the examination of fluids, and the line 
of vision for the worker is the very convenient one shown at F. The 
image of very delicate objects is free from distortions, which is rarely 
the case when using a Nicol’s analyser. 
The analysing eye-piece can be revolved in the draw-tube of the 
Microscope by means of the tube C, giving the usual effects of a revolving 
analyser. 
It is well to use a hemispherical lens of about f in. diameter above 
the selenite film and polarizing prism, with the convex side of the lens 
toward the object upon the stage, and the upper part of this convex 
surface about J in. from the object. 
A modification of the revolving mica film, which I described in 
4 The Omaha Clinic,’ to be used with the Nicol’s analyser, is of especial 
value with the above described eye-piece arrangement, and it is repre- 
sented in figs. 2 and 3. The apparatus consists of a plate of mica placed 
between the analysing plate and the object upon the stage of the Micro- 
scope in such a manner that rotation can be given to it, and it can be 
instantly removed if desired. 
Let fig. 2 represent a side sectional view of the apparatus. C is an 
adapter carrying the rotating mica plate. E is the objective screwed 
into the lower part of the adapter. N is the screw for the body-tube of 
the Microscope. The mica film B is to be cemented between two plates 
of perfectly polished glass F of sufficient thickness to prevent distortion 
of image. r l his disc is to be fitted in the ring A, to one side of which is 
screwed a small handle D, to be used in giving rotation to the plates B F. 
A slit W is cut in the side of the adapter C to allow of the necessary 
motion to the handle D. The amount of this motion is governed by the 
length of the slit. 
Fig 3 is a top sectional view, as indicated by the dotted lines L L 
in fig. 2. The letters in figs. 2 and 3 refer to the same parts. It 
will be seen in fig. 3 that the slit for the rotation of the mica film allows 
180 degrees of motion, which is equal in its optical effects to an entire 
revolution. In selecting mica films great care must be taken to use 
only those which are free from bubbles, lines, and other optical defects, 
and are perfectly clear ; and the richest effects are obtained when used 
in connection with a red and green selenite film placed in its position 
over the polarizing prism, and the mica plate so placed in its plane of 
rotation to the polari scope that it gives a deep, rich violet colour to the 
field of the Microscope. This will be the case if the proper thickness 
of mica film has been selected. 
As before mentioned, it will be noticed that the mica film is placed 
between the analyser and the object upon the stage, and in this position 
it will be found to give new and beautiful effects, in many cases giving 
great boldness to delicate structure.” 
