ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
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surrounded by that of the quartz wedge, and a ready comparison can bo 
made. 
The axial angle apparatus for very small plates, shown in fig. 38, is 
similar to the Schneider-Adams apparatus, in which two small hemi- 
spherical lenses inclosing the plate can be rotated between condenser and 
Fig. 37. 
objective. The base-plate is held on the stage by spring clips. Above 
this plate is the horizontal .axis, carrying at its outer end a divided 
circle, with vernier reading to five minutes. The spindle at the other 
end of the axis A reaches nearly to the middle of the apparatus, and 
Fig. 38. 
is funnel-shaped at its end. The cylindrical bolt B, also funnel-shaped 
at the end, is movable by the screw E in the direction of the axis. By 
left-turning of the mother screw N, a spiral spring drives forward the 
screw shaft, whose end has a funnel-shaped depression in which the end 
of the bolt fits. By right-turning of the screw the shaft is drawn 
