MANIPULATION OF THE MICROSCOPE. 29 
The low-power objectives (those of one-half inch and 
one-third inch equivalent focus) should always be used 
for preliminary exploration before a new specimen is 
examined with the higher powers, since their large field 
of view makes the general relations of the object clear. 
Focusing is also much easier with the lower powers, since 
with them a small object may easily be found, while 
their working distance, or the space between the objec- 
tive and the object when in focus, is great enough to 
allow free play. After placing the object over the center 
of the opening of the stage, the tube should be run down 
by means of the coarse adjustment until the front lens is 
within an eighth of an inch of the object. Then, looking 
through the microscope, the tube is slowly raised by the 
coarse adjustment until the object comes more or less 
clearly into view. It is often helpful to move the slide 
about with the left hand at the same time, as the shadowy 
outline of a moving object is more readily recognized than 
that of one at rest. 
As soon as the object is dimly seen it may be brought 
clearly into focus by the use of the fine adjustment. The : 
proper manipulation of this mechanism is of great im- 
portance, since if the attempt be made to study objects 
which are not well in focus, the eyes will be strained and 
structures incorrectly seen. Furthermore, at any given 
position of the fine adjustment only a certain plane of the 
object examined will be in focus, while its whole figure is 
needed to make up a correct picture. Therefore, one 
hand should be kept continually on the fine adjustment 
while the microscope is in use, varying it slightly as needs 
