72 MACHINERY FOR MAKING THIN SECTIONS OF MINERALS. 
cog wheels or worm-gearing around their own horizontal 
axis; each jaw is also separately adjustable, to and fro, 
by a powerful screw. There are a. number of additional 
adjustments and accessories, by the use of which the de- 
sired plane of section of any specimen, clamped in the 
jaws, can be quickly brought into exact parallellism with 
the surface of the planed iron table, which is the base 
level to which all the movements are referred. A Star- 
rett’s surface-gauge is used in these adjustments. Varl- 
ous forms of special clamps are provided, adapted for 
certain forms which are specially difficult to grasp. 
The thin, and always more or less warped, cutting disc, 
charged along its edge with diamond powder, is held in 
its true level, along the cutting portion, by a peculiar 
contrivance of swinging arms carrying adjustable vertical 
rollers, ten or more in number, half of these above and 
half of them beneath the disc. This device, called the 
‘‘cutting-disc guide,’ proves to be very effective. 
The method by which the disc is more or less perma- 
nently charged with diamond powder isa recent German 
invention, apparently little known, if at all, to our lapi- 
daries, but in use by our lithologists, and much prized 
by them. 
All the parts of the machine are made with great ex- 
actness, and the very best workmanship ; otherwise it 
would be of little value. 
Although the mechanism appears somewhat compli- 
cated, and the various accessories contribute to this ap- 
pearance, yet it is a’fact that there is very little liability 
to get out of order, and the actual working of the ma- 
chine is exceedingly simple. 
Pupils who have no special acquaintance with machin- 
ery yet learn very quickly to cut large sections with it 
with perfect readiness and success. 
This machine is not only destined to become useful to 
scientists, but it also has probably useful industrial ap- 
22 
