27 
be reduced to the diameter of the upper lens of the condenser, by insei-ting a 
diaphragm provided for the purpose, in cases where very small slips are to 
be used. 
The height of stage is in the case of stands II-' to V reduced to the 
lowest limit which will admit of the adaption of the Abbe illuminating apparatus, 
in order that the hands may be supported by the table when manipulating on the 
stage. In the larger stands (I, I", photographic and niineralogical stands) the 
stage is made higher, to facilitate the employment of various methods of illu- 
mination other than by the Abbe illuminating apparatus, which are occasionally 
required. 
Mechanism for moving the object is provided in I, P, 11% the large 
Babuchin, photographic and niineralogical stands. 
This consists of the following arrangements: 
a) Revolution of the stage and body about the optic axis (stand I). 
b) Revolving stage-plate with arrangement for centering (stands I" , II" , large 
Babuchin and niineralogical stands). 
c) Mechanical stage (stand and stand for "photo-inicrography"). The one 
adaptable to stand T' possesses the general arrangement of the English form of 
mechanical stage, and may be substituted in place of the rotating vulcanite stage- 
plate. The micrometer stage of the photo-micrographic stand is made for delicate 
adjustments of the object. 
With stands I, IP, IV, Y and the "Babuchin stand" the "adaptable 
mechanical stage" recently constructed may be used; for very fine lateral 
movements Stage Screw-micrometer No. 31 may be used as a mechan- 
ical stage. 
Mechanical stage movements were formerly peculiar to English micro- 
scopes and were rejected as objectionable by the majority of continental microscopists. 
It is only of late years that they have received more attention on the continent 
and for some years they have formed an object of experiment' also in our works. 
We have arrived at the conclusion that mechanical movement of the object is of 
advantage in the following cases: 
1) In the employment of high power lenses, when it is required to bring a 
point seen at the margin into the middle of the field. This, as is well known, 
when done by hand, is often a sore trial of patience. The small amount of move- 
ment necessary to accomplish this may be effected, to a certain extent, by the cen- 
tering arrangement of the revolving stages of stands P and IP (see above b). 
2) For systematically searching a preparation. 
3) For counting particles within a specified area of the surface of the 
object. 
