506 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
“ ment parallel to tlie glass stage. The imbedded substance is then carried 
“down the main tube of the instrument (which is placed in a horizontal 
“ position) until it presses gently against the microtome-knife, when it is 
“fixed in position within the tube by means of the main draw-tube, the 
“diaphragm of which, either directly or by means of a small wooden 
“ cylinder, is brought in contact with the distal extremity of the substance 
“ to be divided, and this acts as a plug or follower to retain it in position 
“ within the tube. Then, having moistened the knife, and, if necessary, 
“ the substance to be operated on also, the slide-carrier, and with it the 
“ microtome-knife, is made to pass through a sort of revolving cutting 
“ motion, by which the sections are made. These sections may be made 
“ of any degree of delicacy by means of the micrometer-screw attached to 
“ the instrument.” 
The notion of converting such a Microscope into such a microtome 
seemed to be so unique in the novelty of its originality (it is difficult to 
hit on the exactly appropriate designation) that we imported the instru- 
ment from the United States, and give an illustration of it in fig. 54, 
which shows the razor-blade and slide-carrier in the form designed by 
Dr. Hart. 
Alterations in Nobert’s Microscope.* — Herr Kayser describes some 
alterations made on a Nobert Microscope. He particularly mentions 
the simple reading arrangement constructed by him, which is just as 
serviceable as a microscopical one composed of eye-piece and objective, 
but it does not invert the image. This arrangement consists of a small 
tube, containing only a thread and a plano-convex lens. Close to the 
eye comes the thread stretched horizontally, and then the lens, with 
convex side in front, at such a distance that the image of the thread is 
distinctly seen by the passage of the rays through the lens, and reflection 
at its plane silvered surface. A narrow strip of the silvering is removed 
in a direction passing through the centre, and at right angles to the 
thread. Consequently, when the distance of the tube is suitably 
adjusted, the eye can see a division through this central space. In 
order to have the division, but not the thread, more strongly magnified 
than in this, the simplest case, a second plano-convex lens of suitable 
focal length can be added immediately on the plane silvered face of the 
lens. Here two equal lenses of 10 mm. diameter and 25 mm. focal 
length are combined. On the thread end of the tube a white paper 
screen inclined at 45° with central aperture is fitted for the illumination 
of the thread. This small reading arrangement is fastened to the object 
stage, while an ivory rod with a range of 80 mm. divided into half 
millimetres, and fixed vertically on the Microscope-tube, can be dis- 
placed with the tube. A screw with large drum divided into 50 
divisions serves to raise or lower the stage by slow degrees. Since the 
tenth of the division can be easily read, an arrangement is thus attained 
which, over a very large interval (80 mm.), gives an adjustment and a 
measurement which is exact up to 1/1000 mm. This is of importance, 
for instance, for microscopical measurements of the refractive indices of 
transparent plates. By means of the fine screw, the error of the 
divisions on the scale can be tested, and it is especially serviceable in 
* Schrift der Naturforsch. Gesells. Danzig, vii. (1890) pp. xi.-xii. 
