50 
ACCESSORY APPARATUS. 
moving the object, or rotating the eye-piece, the lines can easily 
be brought to measure any object in the field. The object may 
be brought up to the ends of the lines without being covered 
by the micrometer glass. 
With this micrometer, in the eye-piece used for ordinary ob- 
servation, hundreds of objects may be measured, whose magni- 
tude would pass unnoted if it were necessary to change the eye- 
piece to effect the measurement. These advantages, combined 
with the very low price for which it is furnished, will, we think, 
cause this micrometer to be regarded with very general favor, 
and observers who have more expensive micrometers, will find 
it convenient to possess this also. The lines in this micrometer 
are ruled to or 5^0 of an inch, to suit purchasers, but the 
value of the measurements made by them must be calculated 
for each object-glass, in the same manner as with other eye- 
piece micrometers. 
69. Prof. J. li. Smitli’s Ooiiioineter and Micrometer. 
Fig. 22. 
Prof. Smith has invented a Goniometer for measuring the 
angles of crystals under the microscope. It is also combined 
with a micrometer. The following description of the instru- 
ment and the method of using it, are taken from the Appendix 
to Carpenter on the Microscope^ edited by F. G. Smith, M. D., 
American edition. Philadelphia : Blanchard & Lea. 1856. 
E, Fig. 22, is the upper end of the draw-tube of the micro- 
scope with the ring Ic soldered to it. Over this ring screws 
another ring F, which 
serves as a support and a 
centre to the graduated 
circle D, which freely, but 
without shaking, revolves 
upon the same. Into the 
bore of the ring F fits by its 
lower conical end A, tlie 
tube G, which is held in it 
by the screw-ring c>, that 
prevents its being taken 
out. Into the tube G, 
which also has a free re- 
J. & W. GRUNOW & CO’S ILLUSTRATED 
