30 
ZOOLOGICAL EXERCISES. 
practice, as the microscope inverts the object, and 
consequently the movements of the object appear to 
be opposite to those of the hand. Select some spot 
on the object, and place it in the centre of the field. 
Try this several times with different portions of the 
object. Pull out the draw-tube. Focus for the new 
magnifying power. As the magnifying power is 
greater, the objective will have to be approached to. 
the object. Close the draw-tube. Focus. Put in 
the second (deeper) eye-piece. Focus. Pull out the 
draw-tube. Focus. Again practice the manipulation 
of the object on the stage. Put in the first (shal- 
lower) eye-piece, push in the draw-tube, and focus. 
d. Unscrew the inch objective, and put on the quarter. 
Go again through the whole process as detailed in ¢. 
In focussing, use the coarse adjustment until the 
object is indistinctly seen, then use the fine adjust- 
ment to secure good definition. Draw back the 
body, and take off the objective. 
e. Put on the inch objective. Focus. Revolve the dia- 
phragm plate with the finger, and observe the effect. 
fj. Turn the diaphragm plate so that its largest aperture 
is under the stage opening, or remove it altogether if 
the construction of the microscope admits of it. 
Throw the mirror as iar as possible to one side, and 
then direct the light from it on to the object. 
Notice the effect. If done properly, the linen fibres 
will shine out brilliantly on a dark back-ground. 
A knowledge of the appearance of linen fibres is neces- 
sary, as they often get by accident on to a slide, and might 
puzzle the student, or even lead to erroneous conclusions. 
