ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
275 
(about 1745) was even more perfect, for, besides an excellent slow motion 
by micrometer-screw, identical with that adopted about 1835 by the 
German and French opticians, it also carried a micrometer-screw in the 
eye-piece. 
Amongst other Microscopes of the 18th century exhibited was one 
of Dellebarre, presented to the Academic des Sciences de Faris in 1778, 
an inclining Microscope of Navin, a very line instrument in copper gilt, 
with a curious slow motion and a screw motion allowing the horizontal 
displacement of the body-tube ; and, lastly, the Microscope which was 
presented to Buffon by his pupils in 1748. Of the instruments of the 
beginning of the present century, the Microscope of Selligue, the uni- 
versal Microscope of Ch. Chevalier, and the achromatic Microscope of 
Amici were the most conspicuous in the perfection of their design and 
workmanship. 
(2) Microscopes and their Accessories. — The number of opticians 
who exhibited instruments was altogether only eight, viz. Powell and 
Lealand, and Watson and Sons, representing England; Hartnack, 
Leitz, Seibert, and Zeiss, Germany ; Reichert, Austria ; and Nachet, 
France. 
The firm of Ernest Leitz exhibited eight Microscopes, designed more 
particularly for medical and bacteriological researches. Their stand la. 
is similar to the one figured in this Journal, 1889, p. 439, except that 
it is provided with a rotating stage, which can be centered bv a screw. 
The Abbe condenser is moved by rack and pinion, and the iris-diaphragm 
can be displaced laterally by means of a pinion acting on a horizontal 
rack. The oil-immersion objective 1/12 of this firm, with numerical 
aperture 1'30, was highly commended by the jury of the exhibition for 
clearness and exceptional resolving power. 
The firm of Nachet was well represented. Besides the large model 
(No. 1) described in this Journal, 1886, p. 837, they exhibited a very 
perfect instrument specially designed for bacteriological work. Several 
instruments for photomicrography were shown by this firm ; amongst 
them a large inverted Microscope for very high magnifications. The 
whole apparatus is, to avoid tremors, supported upon a large vertical 
tube which forms the base. Amongst the specialities of this firm, the 
adapter, which renders the change of objectives in their instruments so 
simple and easy, is most worthy of notice. 
Powell and Lealand only exhibited one instrument, their stand No. I., 
which needs no description here. Accompanying the Microscope were 
their three apochromatic objectives, the 1/4 in. dry, aperture O' 95, the 
1/8 homogeneous immersion of aperture 1'40, and the 1/10 homogeneous 
immersion of aperture 1 • 50, as well as compensating eye-pieces and 
apochromatic condensers. 
The firm of Hartnack exhibited their stands IV., V., and VI. In 
these the Abbe condenser has the usual disposition, and is provided with 
a slow motion ; the iris-diaphragm can be displaced horizontally by rack 
and pinion. The special models for bacteriological work, like those of 
Zeiss, Leitz, Reichert, and Nachet, have a far from graceful appearance, 
owing to the wide separation of the body-tube from the vertical axis of 
the micrometer-screw. This mode of construction, which is rendered 
more unsightly by reason of the shortness of the Continental tube, is 
