34 
MECHANICAL POETION OF THE MICROSCOPE. 
the centre of the field can be determined by the graduation 
and recorded on the slide. The same object can then be placed 
in the centre of the field of view, at any future time upon any 
microscope having a similar indicator. 
When it is considered that with the higher powers, an object 
measuring only j-Jo or 5 ^ of an inch, fills the entire field of 
view, it will be evident that objects of great interest are 
brought into the field of view a second time with difiiculty, 
and among a number of similar objects, any one which is 
peculiar can only be re-discovered after much patient research. 
But with this indicator stage, if the position of an object has 
been once recorded, it can be found again with great ease and 
certainty. The use of microscopes furnished with this stage 
afibrds great facility for interchanging slides, with the certain- 
ty of finding objects of interest singled out by correspondents. 
53. The Portable Microscope, shown in Fig. 13, is of 
the same size as FTo. 5, but more portable. 
The strong brass legs on which it is mounted, are made to 
fold together, and the compound body, which is attached by a 
bayonet joint, like 'No. 5, can be easily detached, and the instru- 
ment packed in a very small case. 
The arm d, which carries the compound body, can be turned 
away from over the stage. A stout triangular bar, carrying 
the arm d, is moved up and down by rack and pinion connected 
with two milled heads, one of which is marked c. Tlius either 
hand may be used for the quick motion of the body, which is 
effected with great steadiness and freedom from tremor. A 
delicate fine adjustment of focus is obtained by turning the 
milled head a, of a screw which acts upon a lever concealed in 
the arm d ; this lever acts upon a short tube, carrying the 
object-glass, and sliding easily but firmly in the lower end of 
the body. The action of the lever upon this tube is counter- 
acted by a spiral spring, so that an extremely sharp and deli- 
cate motion is obtained. 
The elasticity of the spring diminishes the danger of injur- 
ing the object-glass, if at any time it is allowed to touch the 
object. Great care should be taken that no such accident 
should ever happen. 
J. & W. GRUNOW & GO’S ILLUSTRATED 
