536 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
However, on old stands by Plossl, Merz, Goring, Pritchard, and 
others, it may be seen how for a long time the greatest trouble was taken 
to bring the fine adjustment of the object-stage to an exact and practical 
perfection. So long as the stands are restricted to the usual dimensions, 
there is no reason in particular for compelling us to abandon the good 
and sure movement by prism adjustment ; but if the dimensions of the 
stand should be increased, then necessity would compel us to again fit 
the adjustment to the stage. These ideas have occupied the author for 
some years ; and at last Herr Paul Thate, of Berlin, has constructed for 
him a small model of this movable micrometer stage. The object-stage 
has a diameter of 20 cm., and might have more — a size which, although 
necessary for the observation of large sections, would yet render a suit- 
able stand very massive and awkward. 
For such an instrument the Pacini model of 1845 offers itself as a 
suggestion. The tube is set on a three-sided prism, so that the rays 
which have passed through the object are reflected at an angle of 
30°, and hence the oblique position of the tube need not be worked by 
means of the movement ot the stand. Thus the great advantage is 
gained of being able to place the preparations horizontally. Pacini 
moves the stage by a micrometer-screw, which is fastened to the stand, 
and possesses a short inclination to the movable disc. This micrometer 
movement is not exact enough to satisfy modern demands. If the stage 
is moved, it is obviously required that every movement of the stage 
must be strictly central. There must be no shaking of the object ; 
there must be steady up-and-down motion, without being in the least, 
brought out of the axial setting. Such a motion can be attained by 
fitting an inner cylinder to the object-stage, and fixing it with clamps, so 
that it can be moved up and down by means of a screw-disc. This 
screw-disc js placed round the cylinder and fixed in a slot, so that the 
rotation of the screw raises and lowers the cylinder. The larger the 
dimensions the finer is its movement, and every difference in height can 
be read off on the disc, which is provided with scales. The mechanical 
arrangement is less complicated than other contrivances which have 
been, and perhaps will yet be, applied to the upper stand if the need for 
large stands should become more marked. It is already a hindrance 
that the movable tube hangs on the same part which encloses the whole 
fine adjustment, and many a micrometer movement has been ruined by 
inadvertently lifting the Microscope by the arm. But the beginner will 
always use the arm for gripping the Microscope. 
The application of the Porro system to microscopy will give a 
further stimulus to the production of new stands. The oculars will 
first be constructed out of prisms, which, just as in the case of telescopes, 
will procure their highest optical adaptability, and similarly will permit 
a shortening of the tube, and will attain with the strongest magnification 
a brilliant and large field of view. One ought to see the attention of the 
up-to-date Microscope constructor directed to the combination of Porro’s 
oculars with large object-stages and with the most delicate adjustment 
motion of the object-stage. 
We are by no means at the end of the constructive adaptability of 
our optics and mechanics, and many a discovery yet slumbers in the 
workshops of our Microscope makers. 
