ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
105 
of 160 mm. a magnification of twenty times was obtained, for a focal 
distance of more than 30 mm. 
The difference in height of the growing plant can be determined 
with this instrument in two ways. One method consists in adjusting 
on a determined fixed point in the Microscope at the beginning and end 
of the experiment, each time taking the reading on the vernier. This 
determination is, however, only exact to about 0*1 mm. The more 
precise method is to take a reading on the micrometer at the beginning 
and end of the experiment. A difference in height of 0*06 mm. can 
then be directly determined, and a difference of 0*03 mm. can be con- 
veniently estimated. 
Leitz’s Mechanical Stage.* — This stage, shown in fig. 2, is ad- 
apted to the Leitz stands I., la, and II. The movement from front 
to back is effected by two racks and pinions, that from right to left by 
means of a screw. The movements are measured by two millimetre 
Fig. 2. 
scales. To fit the stage to the Microscope the screw on the right is 
loosened so that the arc lever can turn about the axis. The stage is 
then placed on the ordinary Microscope stage, so that the angle-pieces 
opposite the lever are in contact with the column ; the lever is then put 
in its place and the screw fastened. Lastly, the stage is fixed to the 
column by means of the other screw. 
* Catalogue No. 34 of Microscopes and Accessory Apparatus. Ernst Leitz, 
Wetzlar, 1892, p. 45. 
