71 
an object; the real value of the divisions must, therefore, for 
exact measurements, be determined by means of the stage micro- 
meter for each pair of objective and eye-piece at definite tube 
lengths. Approximate values, sufficiently accurate for ordinary 
measurements, may, in the case of No. 28, be taken from a table 
supplied with these, in the case of No. 29 they may be found 
from the focal lengths of the objectives. (Fig. 30.) Inch bone 
capsule 
The following instruments are provided with this micrometer 
supplied separately in capsule: Nos. 28, 28% 29 and 29 \ 
Micrometer Eye -piece for ordinary objectives. Huy- 
glienian eye-piece (2 or 3 as desired) with adjustable eye-lens 
for exact adjustment of the micrometer scale to the eye of the 
observer ; with table of the micrometer values of the divisions. 
(Fig. 31,) Inch micrometer No. 27 • 
Fig. 31. 
Micrometer Eye-piece. 
id. Micrometer movable laterally by means of a 
screw 
Id. With movable index in lieu of the micrometer . . . 
The micrometer disc or the index — which is 
fixed to a ring and may be procured singly at M. I.— 
are supplied in small ivory capsules together with 
the eye-pieces. The tube of the eye-piece consists 
of two parts and may be screwed asunder, the line of 
