ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
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preparation there are three small tubes in the stage, by which a stream 
of air can be directed upon its under side. Instead of the black cover of 
the old instrument, two screens are found to be sufficient to prevent 
the dispersion of the light. One of these is hinged to the holder of the 
totally reflecting prism, while the other is fixed horizontally above it. 
The prism is made of a specially strongly refractive glass of the 
firm of Zeiss, since by the use of ordinary glass a part of the field of 
view is cut off by total reflection. 
Remarking on this paper,* Herr R. Fuess takes exception to the 
remark, that the old form of instrument, whose construction was 
undertaken by the firm of Fuess, has the great drawback that it is 
not possible to observe the preparation between crossed nicols during 
the heating. To prevent misunderstanding he states that he did 
actually at one time undertake the construction of the Microscope 
described in Zeitschr. f. Instrumentenk., 1886, p. 325, but that pressure 
of business prevented him from attempting any technical improvements 
in the instrument, and at length compelled him to relinquish the 
undertaking altogether. He wishes it, therefore, to be clearly under- 
stood that no Lehmann Microscope of the form described has been 
made by him. He adds, that some years ago he constructed a heating 
apparatus for his crystallographic Microscopes, by which the preparation 
could be heated to a clear red glow during observation between 
crossed nicols. 
Van Heurck’s Microscope for Photography and High-power Work. 
— The following description of this instrument (fig. 45) is translated, 
with modifications, from the fourth edition of Dr. Henri Van Heurck’s 
work on * The Microscope,’ which is now in the press : — 
“ In the Microscope which W. Watson and Sons have made to our 
specification we have attempted to combine convenience for ordinary 
work with the utmost possible precision, and at the same time to keep 
the price comparatively low. 
Messrs. Watson have admirably carried out all the plans we sub- 
mitted to them, and the instrument they have produced may be justly 
considered as realizing in various ways a degree of perfection which has 
never hitherto been reached. 
The base of the instrument is of the horseshoe form, bronzed; at 
the three points on which it stands slightly projecting pieces of cork 
are inserted, which reduce the tremor, prevent the instrument from 
slipping, and the table from being scratched. 
A substantial brass pillar, jointed in its upper part to allow the 
inclination of the instrument, supports the Microscope, which can be 
fixed at any angle by means of a clamping screw, although the instru- 
ment is so well balanced as to render this screw almost superfluous. 
To increase the general stability, all the parts of the instrument 
have been made as if they were cast in one piece. The stage-support is 
made of a single piece, and is prolonged into the articulation of the top 
of the pillar ; the limb fits into the stage-support and is fixed by six 
screws, so that the whole has the same rigidity as if it formed a single 
* Zeitschr. f. Instrumentenk , x. (1890) p. 261. 
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