ZOOLOGY AND BOTANY, MICROSCOPY, ETO. 
269 
piece at the other side of d, in which d slides, would have to be 
screwed to a revolving ring of the permanent Microscope stage. The 
revolution could not, however, be complete on account of the projecting 
part of a. 
For the recording of the position of objects a scale is cut across the 
stage, and another along the edge of the frame or long arm of the clip, 
and the holes in b are numbered so that positions at the very opposite 
ends of even large culture plates could be noted without difficulty. 
It remains to be stated that I have tested the stage witli high and 
low powers, with large and small slides, with series of sections, with 
troughs, and with watch-glasses, and found that it fulfils all reasonable 
requirements. For watch-glasses a brass plate is either clipped or still 
better carried on a frame, the Microscope being placed upright. The 
watch-glass rests in a hole cut out of this plate. A plate of wood or of 
thick cardboard would of course serve almost as well as one made of 
brass. 
The firm of Carl Zeiss is famous for the excellence of the work it 
sends out. If the new mechanical stage does not prove to be the boon 
to microscopists which I anticipate, the fault will lie in the design, and 
certainly not in the way the designs have been carried out. If, on the 
other hand, the stage or some modification of it be generally adopted, it 
will hut add one more to the long list of valuable additions to the science 
of microscopy which have issued from the enterprising firm of Carl 
Zeiss of Jena. 
(4) Photomicrography. 
Photomicrography.* — Mr. A. Pringle gives a brief sketch of the 
various improvements in photomicrography, which have been made 
within the last two or three years. One of the most important is the 
improvement in colour-rendering, due to orthochromatic photography. 
Of no less importance is the remarkable improvement in optical methods 
which we owe to the so-called Jena glasses. In the production of these 
glasses it was found possible to obtain different relative proportions of 
refraction and dispersion, the result of which has been a set of objectives 
in which the achromatism reaches “ an almost ideal point of perfection.” 
The value of these apocliromatics is more especially felt in photography, 
for besides giving better correction these glasses also enable us to obtain 
a much greater angular aperture, and consequently more perfect 
definition. 
Amongst slight improvements in the ordinary apparatus the author 
mentions the strong rigid support for the ocular end of the Microscope, 
which is a feature of the instrument designed by himself and Mr. Swift. 
This support is very necessary in work with high powers in order to 
prevent tremors during the exposures. 
Having mentioned the more evident improvements in apparatus and 
methods, the author proceeds to treat of the various difficulties met with 
in high-class work. The first difficulty considered is that of illumina- 
tion. For work with high pow r ers it is essential that the substage 
condenser and the objective should bear some relation to each other in 
angular aperture and also in focal length. In low-power work the even 
* Journ. and Trans. Photographic Society, xvi. (1S91) pp. 71-9. 
1892. ' U 
