392 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
MICEOSCOPY. 
o. Instruments, Accessories, &c* 
(1) Stands. 
Some Improvements and Additions to the Microscope Stand.j — 
Herr J. Amann points out some slight improvements and additions to 
the Microscope stand which might be easily realized without raising the 
price of the instrument to any great extent. 
In the first place, he considers that, at least in the larger stands, the 
lens-system of the Abbe condenser should be made perfectly centering, 
and remarks that the centering of the condenser has for a long time 
past been regarded by English authorities as an indispensable condition 
for any perfect Microscope. 
The method of introducing the polarizer employed in most Continental 
stands, viz. by supporting it in the diaphragm-holder of the condenser, 
is also capable of improvement, and a simple arrangement which would 
allow gypsum and mica plates to be rotated independently of the polar- 
izer in a plane at right angles to the optic axis of the instrument is 
much to be desired. 
A further desideratum concerns the use of the fine-adjustment for 
exact measurements in the direction of the axis. By long use of a Fuess 
stand, in which the fine division of the screw-head allowed of readings, 
with the help of a vernier, of a thousandth of a millimetre, the author 
has convinced himself that an exactness of from 1 to 2 p, can be attained, 
and that the usual division of the screw-head into 0*01 mm. is not suf- 
ficient to bring out the advantages of the present highly perfect con- 
struction of the fine-adjustment. For the coarse-adjustment a division 
which would allow the displacement of the whole optic system to be 
measured, would be very useful, e.g. in the determination of the focal 
length of lens-systems. Such a division could be easily made on the 
body-tube, while a fixed index, or better still, a vernier, was screwed 
to the arm which connects the body-tube with the fine-adjustment. 
It would be further desirable that in all stands the diaphragm on 
the lower end of the draw-tube should be provided through an interme- 
diate piece with the English or Hartnack screw, in order to be able to 
adjust weak objectives on the upper focal plane of the stronger objective 
which serves for the observation. This simple arrangement serves a 
number of useful purposes ; it allows of the micrometric measurement 
of the iris of the objective, and thus of the numerical aperture ; the ob- 
servation of the diffraction spectra and that of the axial figures in con- 
vergent polarized light ; it simplifies further the introduction of an 
analyser immediately above the objective. This arrangement of the 
adjustment of the Microscope on the upper focal plane of the objective 
is besides indispensable in the use of the micro-refractometer. 
Finally the author expresses the wish that the lacquer of the lower 
part of the objective should be replaced by an electro-deposit of platinum 
* This subdivision contains (1) Stands ; (2) Eye-pieces and Objectives ; (3) Illu- 
minating and other Apparatus; (4) Photomicrography; (5) Microscopical Optics 
and Manipulation ; (6) Miscellaneous. 
t Zeitschr. f. wiss. Mikr., xi. (1894) pp. 1-4. 
