92 BROOKES, ON MICROSCOPES IN THE EXHIBITION. 
scope,’ consisting of a microscope-body mounted over a large 
revolving brass drum, in the interior of which are placed a number 
of independently revolving cylinders, which traverse as they rotate, 
by the aid of a many-threaded screw. The objects, 500 in 
number, are placed spirally round the hollow cylinders, and are, 
by appropriate and simple mechanism, brought successively into 
the field of view, being illuminated by a reflector placed inside 
the cylinder. This elaborate contrivance is well adapted for the 
purpose for which it was designed, and will effectually protect the 
collection of objects from dishonesty, as well as from carelessness. 
Several new accessory apparatus are likewise comprised in this 
collection. Besides the double nose-piece now generally in use, 
there is a quadruple nose-piece, for mounting four object-glasses 
simultaneously, either of which may be brought into the axis of 
vision. This consists of a revolving piece, with four bent arms 
attached to the body of the instrument, so that the axes of the 
four objectives lie in a conical surface, one side of which is 
coincident with the axis of the body. The weight of this 
apparatus, when loaded with four objectives, will be nearly twice 
that of the double nose-piece; and its greater convenience is 
perhaps open to question ; moreover, it is thought to be impossible 
that the fine adjustment can work with the delicacy essential for 
high powers, when its spring is so heavily and so unnecessarily 
loaded. There is also a very ingeniously contrived opaque object- 
holder, in which, by a simple and effective means of complete 
rotation in two planes perpendicular to each other, the point 
of surface under examination may be placed in any required 
position. 
This firm also exhibits a variety of pieces of brass-work in all 
stages of manufacture, from the rough casting to the finished 
work, showing the beneficial action of planing, shaping, and 
slotting machines, designed and constructed by themselves, on 
the well-known and established principles now generally adopted 
in mechanical engineering. 
J. Swrer (United Kingdom, 2974) exhibits a microscope stand, 
in which a chain-moyement is concealed in the triangular sliding- 
bar and its stem, and the rectangular motions of the stage are 
effected by eccentrics. The chain-movement necessarily gives 
great smoothness of motion; the advantage of the stage-movement 
is somewhat questionable. 
F. H. Wenuam, M. (United Kingdom, 2989), exhibits his now 
well-known and duly appreciated binocular arrangement, which 
has already been alluded to (p. 22); the most perfect stereoscopic 
effect is thereby produced, without the definition of the object 
being sensibly impaired. This is due to the entire absence of 
chromatic dispersion, the deflected pencil being perpendicularly 
incident on, and emergent from, the corresponding surfaces; its 
change of direction is solely due to internal reflection. If the 
displacement of the pencils be effected by refraction, some amount 
of chromatic dispersion is unavoidable, which has been found to 
