BROOKES, ON MICROSCOPES IN THE EXHIBITION. 91 
dary stage for the adaptation of all varieties of illuminating and 
polarizing apparatus is readily mounted and dismounted, and 
possesses vertical and rectangular horizontal adjustments, as well 
as circular motion, the rings both in this and the upper stage 
being graduated. 
Of the objectives it is difficult to say too much; the correction, 
and consequent defining power of all is excellent, and in the 
medium powers especially the flatness of the field and the accu- 
racy of definition over its entire surface are most remarkable ; 
the low powers (meaning objectives of one-inch or longer focus) 
are by no means excluded from this category ; but in these, good 
results in this direction have been long since obtained, and, more- 
over, the attainment is comparatively easy. 
In addition to the usual forms, a Kelner’s achromatic eye-piece 
is exhibited, by which the usual area of the field of view is 
doubled, but not, it is thought, without a considerable sacrifice 
of definition. This differs from the ordinary Huyghenian eye- 
piece in having a double convex field-glass and an achromatic 
meniscus eye-glass. 
Of illuminating apparatus, Mr. Ross exhibits a modification of 
his well-known Gillett’s condenser, specially adapted for the lower 
powers; and in addition to all other established forms, we find 
the hemispherical condenser above mentioned, now commonly 
known as “ Reade’s kettle-drum.’’ Darker’s selenite plates are 
here very conveniently adapted to the polarizing apparatus. 
Amongst a great variety of useful accessory apparatus, a new 
form of compressor is exhibited, in which, by means of a short 
vertical slide, the upper plate of thin glass is moved parallel to 
the plane of the instrument. 
Smitu, Brox, & Brox, M. (United Kingdom, 2964), present a 
copious display of microscopes of various capabilities. One of 
their large first-class instruments is rendered very portable, by 
making the legs to fold up; the stage also is removable; it is 
packed in a comparatively small flat case, replete with every con- 
ceivable accessory apparatus. 
The first-class instruments by this firm have long been duly 
appreciated by the public, but their efforts, which were considered 
most praiseworthy and successful, were those directed to the 
production of students’ microscopes of various kinds, of good 
working quality, and at a very moderate price, by the aid of an 
extensive plant of machinery. Perhaps the most conspicuous of 
these is a binocular microscope, which is rendered complete with 
eye-pieces, and two objectives, at £10, about the same price as 
that usually charged by themselves, and the other first-rate firms, 
for merely adapting Wenham’s binocular arrangement to an 
ordinary first-class instrument. The student’s microscope, firmly 
supported on a solid circular base, comprising two fairly good ob- 
jectives of one-inch and quarter-inch focus, and sold complete 
for £5, is a highly commendable instrument. 
This firm exhibits as an undoubted novelty a “ Dlusewm Micro- 
