ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
687 
that, notwithstanding their great focal length, the body of the Microscope 
remains at its ordinary elevation. 
The objective a* (fig. 108) consists of two achromatic lenses com- 
bined after a special formula. The distance between the lenses can be 
Fig. 108. 
Fig. 109. 
Fig. 110. 
varied by the ring R R ( like a correction-collar, so that when one of the 
lower eye-pieces is used the magnification can be varied in the proportion 
from about 1 to 2. 
The new objective D* is a water-immersion lens of great focal length, 
but with a relatively small aperture. It is intended for the examination 
of living zoophytes and plants floating in water- 
troughs. 
Zeiss’ Projection Eye-pieces.* — These eye- 
pieces (see fig. 109) consist of a collective lens and 
a compound system which is corrected spherically 
and chromatically after the principle of apo- 
chromatic lenses. A diaphragm is placed be- 
tween the lenses, and the compound lens can be 
made to approach it or recede from it. 
(3) Illuminating: and other Apparatus. 
Correction Adjustment.!— In fig. 110 is seen 
the construction of the Zeiss correction arrange- 
ment. The ring b b serves to adjust the dis- 
tance between the two upper double lenses and 
the two lower lenses attached to the mounting a a. uuwluuo 
the collar b b indicate for each position of the collar that thickness of 
cover-glass which gives the best correction for that position.; The 
* Zeiss’ Catalogue, No. 30, 1895, pp. 20-1. 
The divisions on 
f Tom. cit., p. 5. 
