102 
Beck, on a Revolving Disc-holder. 
ments, and in no one direction can an object be turned about 
quickly and with certainty under moderately high powers. 
The instrument which I have used myself for some time 
with considerable advantage is shown in fig. 1. 
Fig. 1. 
Tig. 
A brass plate {a), which is adapted for clamping in the 
ordinary way upon the stage of the microscope, has a hole 
through it sufficiently large for a low-power Lieberkuhn. On 
the right side, at [h)j is attached a short upright stem, 
which turns at its base ; and at its top is another fitting, in 
which the arm (c) can be revolved by a milling at (d) ; but 
the most important movement of all is the rotation of a 
small socket (e), at the extremity of the arm (c). This is 
accomplished by means of a fine chain, which communicates 
with the milled-head (f). The object is gammed upon a 
small disc (g), which fits in the socket at (e), and with the 
arrangements I have already described, as many as five sides 
of a cube may be examined with perfect ease, and without 
disturbing the position of the object on the disc. 
To preserve those objects 
which are permanent, the box, 
fig. 2, may be used. It will 
contain twenty-four discs, and 
the holes in which they fit 
being numbered, the objects 
may be easily registered; the 
top of the box on the outside 
will also hold a paper label. I 
may mention, in addition, that 
a wire is attached to the out- 
side case of the box as a guide, 
to prevent rubbing off" the objects when it is screwed on. 
The space between the inner and outer cases is also so 
arranged, that if a disc should shake loose, there is no room 
for it to get quite free, and tumble about to the injury of the 
other specimens. 
Each disc has a small groote Ofi the edge to facilitate its 
"1 
J 
