90 BROOKES, ON MICROSCOPES IN THE EXHIBITION. 
of this old-established and much respected firm was of very limited 
extent, but at the same time of first-rate excellence. The form 
of stand now generally adopted by them is a tripod, combining 
steadiness and stability with comparative lightness: as the stability 
of the instrument here depends on breadth of base in place of 
weight of foot. The object-stage has a concentric circular motion, 
in addition to the usual rectangular movements. The rectangular 
movement-plates are made extremely thin, and are raised by a 
kind of flat pillar from the rotating ring, for the purpose of 
allowing rays of the utmost obliquity to be thrown upon the 
object by an Amici prism. The sharply accurate definmg power 
of their objectives has scarcely been exceeded, and not often 
equalled, especially in those of most difficult execution, the 34th 
and 51th; but their greatest triumph is in the production of a 
perfectly defining objective of th or s;th-inch focus, working 
very satisfactorily through a covering-glass of 0:035 to 0°004-inch 
thickness. Nor is it to be supposed that this immense magnifying 
power, ranging as it does from about 1700 to upwards of 3000 
diameters, that is, in round numbers, from three to ten millions in 
area, is a mere philosophical curiosity ; we cannot doubt that the 
wonders of creative beneficence will be developed in proportion 
to our extended means of investigation; and the writer can fully 
testify to having repeatedly seen, under one of these objectives, 
evidences of structure that are, under ordinary powers, utterly 
indistinguishable. This firm also exhibits a compact form of 
portable microscope, in which the three legs of the tripod fold 
together; and a very convenient form of illuminating apparatus, 
which has been already alluded to. They have not devoted their 
attention to the manufacture of anything but first-class instru- 
ments. 
The Rev. J. B. Reapz, Hilesborough, H. M. (United Kingdom, 
2948), exhibits a hemispherical condenser, which has been found 
to possess remarkable powers in developing the markings of 
diatoms, with objectives that were unable to accomplish the same 
with any previously known simple means of illumination. The 
construction of this apparatus has already been sufficiently de- 
scribed. 
T. Ross, M. (United Kingdom, 2952), exhibits a remarkably 
fine collection of first-class instruments and apparatus, for every 
kind of microscopical investigation. These instruments differ 
in quality, and correspondingly in price, only in relation to the 
completeness of their mechanical arrangements, the workmanship 
of all being equally good, so far as it extends. The optical parts 
of all are alike, both ocular and objective, none of a second or 
inferior quality bemg manufactured. The stage arrangements 
are most perfect ; the thin traversing plates of the object-stage 
are attached to a rotating ring, believed to be of such diameter as 
to admit to the under surface of the object any oblique illumina- 
tion that can possibly be required. ‘This form of stage was 
generally admitted to be the best in the Exhibition. The secon- 
