692 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
centre of two flat brass plates, long enough to extend beyond the stage, 
is a 3/4-in. bole slightly recessed to receive a 7/8-in. No. 2 cover-glass, 
and at each end a screwed stud is fixed to receive mill-edged nuts for 
compression. The holes in top-plate are slotted through on one side 
in order to remove the plate by unscrewing the milled-edged nuts and 
lifting the plate above the steady-pins which are fixed at each end to 
prevent any lateral or longitudinal motion ; the bottom plate (or both 
plates) has a transverse chase cut in to receive two springs to keep the 
plates apart, but sufficiently flexible to allow them to come into contact. 
The above plates may be made solid or perforated in order to lighten 
them, and the cover-glasses may be oblong and slipped under spring 
clips, two on each plate. The steady-pins may be dispensed with by 
having the under side of milled-edged nuts made conical and the top- 
plate coned to receive the same. These compressors may be made any 
length, to suit different stages. 
Application of Polarized Light to Histological Investigations.* — 
Dr. H. Ambronn suggests, in the modest little work he has just published, 
that polarized light might be occasionally useful for histological purposes. 
This is quite possible, but it would be well to show what practical results, 
however small these may be, have been obtained in addition to describing 
polarization phenomena. 
(4) Photomicrography. 
Apparatus for the Projection of Microscopic Images. f — The firm 
of Carl Zeiss publish details of the latest changes in the construction of 
their photomicrographic apparatus, by which it is rendered more suitable 
for purposes of the projection of images on a screen. 
As source of light they recommend the electric arc projection lamp 
of S. Schuckert and Co. of Niirnberg which, with a current of 16 am- 
peres and 60 volts, gives a light of about 2500 candle power. The 
regulation of the distance of the carbons is effected very readily at any 
moment by means of two screws. The special feature of the lamp is 
that the carbons are not placed vertically but obliquely. The advan- 
tage of this is that the light of the glowing hollow in the positive carbon, 
which is generally lost, is to a large extent utilized ; so that such lamps 
give in the direction of projection, for the same current, a more intense 
illumination than other systems. The projection table (fig. 99) carries 
at one end the lamp C, and at the other the Microscope M, with the 
optical bank D D between. 
The Microscope is attached to a base-plate which can be adjusted 
in height, and also to the right and left, by means of a rod passing beneath 
the table, so that the axis of the Microscope can easily be brought into 
coincidence with that of the apparatus on the bank. 
The chief requirements of a Microscope for projection work are : — 
(1) A mechanical movable stage with micrometer movements. 
(2) A sliding objective changer. 
(3) A condenser which can be adjusted in two directions at right 
* ‘ Introduction to the Use of Polarized Light for Histological Kesearch,' 
Leipzig, 1892, 59 pp M 8 pis., 27 figs. See Bot. Ztg., li. (1893) pp. 122-3. 
f ‘ Carl Zeiss Optische Werkstatte,’ Jena, 1892, 17 pp., 9 figs. 
