140 
upright rods which pass down through the base and are fastened 
by nuts, both on the lower side of the base and on the upper side 
of the top (Fig. 24). 
The instrument is furnished with fine adjustment only, and the 
milled head is removed, allowing the top of the case to rest on 
the head of the support. The square head of the micrometer 
screw projects through a small aperture in the plate and is man- 
ipulated by a detachable key kept by an attendant. The upper 
felt in such manner as to be dust-proof. The instruments are 
fitted with ocular II. and objective 3, giving a magnification of 70, 
but this combination may be changed from time to time. 
Fic. 25. Exhibition Microscopes mounted on table. 
The instruments are fastened in pairs to tables of special design 
(Fig. 25), and placed in the west hall of the systematic museum. 
The objects placed under observation aid in the illustration of 
exhibits in the cases. Suitable explanations are given by labels 
