72 
division being just above the diaphragm. Upon this 
diaphragm the ring with pointer or the micrometer- 
disc, as the case may be, should be placed, the latter 
in such a position that the figures appear erect, and 
then the two parts screwed together. 
^Micrometer Eye-piece for the apochromatic Objectives. 
Compensating eye-piece 6 with '/i micron divisions. The 
divisions in this eye-piece are so computed that the value of one 
interval (with a body-length of IGO mm) for each apochromatic 
objective equals just as many micra (.i (0,001 mm), as there are 
millimeters in its focal length, i. e. 
Apochromatic lens: 16 mm 8 mm 4mm omm 2.5 mm 2 mm 1.5mm. 
Value of interval: 16 8 ^< 4 "6 f.i 2.b 2 {.i l.b u. 
A table of values is, therefore, superfluous for 
this eye-piece, since the focus of these lenses in- 
dicates, accurately within 5 "/o, these micrometer 
values 
icrometer scale laterally adjustable by 
m e a n s 0 f a s c r e w 
Fig. 32, 
Screw Micrometer Eye- piece. 
