24 Microscopes at the American Exhibition. By J. G. Hunt. 
measurement of the angular aperture of objectives. The top of the 
stage is elevated accurately to a level with this centre of rotation, 
and revolves concentrically around the focal point. The stage is 
accurately graduated, and is adjusted by screws which are turned only 
by screw-drivers, and when once centred is not easily disarranged 
by careless trifling with inviting milled-head screws. All the illumi- 
nating apparatus, including the mirror, turns around the same 
centre, remaining always in focus, and all degrees of oblique light 
from 1 ' to 90 J , are read off at sight on a graduated index level with 
the stage. This obtaining and registering of obliquity was perfected 
two years ago, and similar facility is not found in any other micro- 
scope. Its scientific value is apparent.* By turning a large milled- 
head screw a stage of extreme thinness, which likewise rotates con- 
centrically, may he substituted for the longer one, and now your 
achromatic condenser and mirror may rise above the stage for 
illumination of opaque objects, and still the degrees are registered. 
The fine adjustment has been removed from the end of the body, 
the wart has been operated upon, not by Esmark’s, but by Zent- 
mayer’s process, and not a drop of blood was spilled. It has dis- 
appeared entirely. Still a peculiarly shaped, large milled-head 
graduated screw, which gives a comparatively rapid or extremely 
slow motion, moves a slide independent from the rack-motion, and 
focusses the entire optical body, thus always preserving the same 
relationship between the objective and eye-piece, an arrangement 
not found in any first-class English microscope. The binocular 
prism is ground with equal skill and adjusted with more care than 
in most other instruments that have ever come under my examina- 
tion ; hence, both fields appear coincident, and do not resemble the 
longitudinal section of a cylinder, one side up, quarter way round 
depressed.! Here, then, we have a microscope of home production, 
but of surpassing precision, and which has taught the skilled 
English makers a useful lesson. If they propose to compete for the 
American market they must send hither better work. Thus far I 
have spoken chiefly of first-class microscopes, and only of those 
which have come under my notice. 
The so-called student’s stands are of equal importance, though 
less elaborate. All makers, foreign and domestic, furnish enough 
of these. Some are fit instruments for scientific work, very well 
adapted to the coarser observations in biology ; but most of this 
* It is stated in the ‘ American Naturalist’ for December, that a firm from 
Rochester, New York, “hinged the sub-stage bar at the level of the object,” but 
the small stands exhibited by said firm at the opening of the Exhibition were not 
so made, neither had they any facility for registering obliquity. The firm in 
question did not grasp Zeutmayer’s idea at all, and hence can justly claim no 
priority of invention. 
t The sub-stage is cut entirely through transversely, which gives unusual 
facilities for accessory illuminating apparatus. 
