4) For registeriijg certain spots in specimens in order to readily rind them 
again. 
5) For the projection of real images. 
In cases 2 to 5 a mechanical stage like the one of stand I^, or of the plioto- 
micrographic stand or the adaptable mechanical stage will be found a more or less 
indispensible adjunct. These are all so constructed as not to interfere in the least 
degree with any other manipulative process, and they may be retained in situ even 
when using pure-cultivation plates. We consider this to be a great improvement 
on the older form of mechanical stages, which must be removed from the stand 
during certain investigations with the instrument. 
If the divided scales, with which the mechanical stages are provided, are to 
be used as means for refinding a particular spot of a specimen, the 
following points should be observed : 
a) In the case of the mechanical stage of stand care should be taken that 
in the interval between searching and refinding the centering screws should be 
left in an unaltered position. 
b) The small adaptable stage should remain in a fixed position or should 
always be adapted to the stand in the same position (the small indentation produced 
by the fixing screw may be used for this purpose). 
c) In both cases the slip should be accurately brought into its original 
position. 
If it is desired to mark a specimen in such a manner that a particular spot 
may without difficulty be found by different observers using different instruments at 
different places, the best plan would be to mark any part of either the slip or the 
preparation itself in a conspicuous manner, say by means of a diamond cross, and to 
note the exact distance in both coordinates of the particular spot which is to 
be refound from that mark. The second observer will, in proceeding from this mark, 
have no difficulty in refinding the desired spot by means of his mechanical stage. 
As a matter of course , a lower power should be used to refind a spot 
and bring it into the centre of the field previous to examinations with a high 
power lens. 
B. The Adjustment of the Objectives. 
The coarse adjustment. Whilst the coarse adjustment, in its form by 
means of sliding tube as retained in the cheaper stands V, VI and VII, has 
undergone scarcely any alteration since its introduction, the rack and pinion 
motion of all the other stands has already some years past been very consider- 
ably improved by us. We have constructed special machines for the accurate 
production of the (diagonal) gearing, and this motion is now made so perfect that 
objectives of medium power can be focussed by it alone without recourse being 
had to the micrometer screw. 
