24 
PRACTICAL PHOTO-MICROGRAPHY. 
“ When the desired field is seen, the slide is firmly 
fixed by the clips; the long thin bar of the apparatus 
is then inserted beneath the clips, and the rectangular 
elbow formed by the junction of this bar with the body 
is closely applied to the slide. This being made sure of, 
the screw beneath is tightened so that the frame is firmly 
held in position. The slide is now removed and the 
finder substituted for it, and the number read off,” etc. 
When it is desired to refind the held the apparatus is 
placed upon the stage with the finder in its angle, the 
required number found, the frame fixed in position, and 
the slide substituted for the finder.” 
The fitting of the mechanical stage should be as 
accurate as any part of the stand, otherwise great 
vexation will arise. Nothing is more annoying than a 
stage so badly made that the object keeps moving out 
of sight, or out of focus, at every movement of the 
mechanical stage. The slide, i.e., the preparation, 
should never be clipped down to the stage-plate by 
springs as is so common—at all events the clips should 
be quite weak, just strong enough to keep the slide in 
place ; the proper clips act on the edges or ends of the 
slip. We do not know of any mechanical stage so good 
in all respects as that of Powell and Lealand, and in 
pointing out some of its excellences we shall be stating 
the desiderata for such a stage. The motions in both 
directions are effected by racks and pinions, and as 
these are worked the milled-heads do not move away 
from the hand. The stage-plates move on properly- 
shaped grooves, the fittings being sprung as described 
