THE YOUNG SCIENTIST. 
57 
! edly the best.- Considerable difference of 
I opinion exists as to how the microscope 
I should be placed in regard to the light, as, 
i ioY example, whether it should be placed 
directly in front of the lamp or window, 
I or to one side. To us it seems of little 
I consequence, so long as the light falls full 
I ^nd fair upon the mirror, while the ob- 
ji server's eyes are completely shaded. A 
I Tery sifiiiple arrangement of blackened 
paper or pasteboard will effect this, but 
if no such shade is at hand, the micro- 
scopist should sit with the lamp or win- 
dow at his left hand, and his face di- 
rected to some comparatively dark part 
of the room. 
The microscope being i^laced so that the 
1 light may fall on the mirror, the next 
'\ step is to reflect a beam of light up through 
jl the microscope. The easiest way to do 
I this is to place a transparent object on 
|i the stage, and turn the mirror until the 
iDeam of light falls squarely on it. Then 
[I look through the microscope, and if the 
|| field of view is not fully and equally il- 
II luminated, turn the mirror until by re- 
; peated trials this defect is removed. We 
I are now ready to look at the object. It is 
! supposed, of course, that the beginner has 
I screwed on his lowest power ; this is easily 
managed and will show a section of wood 
very well. Bring the objective down to 
within a quarter of an inch of the object, 
and while doing this do not look tJu^ough 
I the microscope, but watch the objective 
and the object from the outside. Then 
apply the eye to the eye-piece, and slowly 
move the body of the microscope, and 
with it, of course, the objective, upward, 
until the object is seen clearly and dis- 
tinctly. 
Before placing an object on the stage, 
see that the objective is raised at least half 
an inch above the stage, and when using 
liigh powers, never attempt to introduce a 
new slide without raising the objective ; 
otherwise you run great risk of injuring 
both the object and the objective. This cau- 
tion is peculiarly necessary, because in a 
little book that has been widely circulated 
directions the very reverse of these are 
given, and we are told to "1. Bring the 
objective down close to the stage. Do this 
'before looking through the microscope. 
2. Place on the stage the object to be ex- 
amined." It would be impossible to sug- 
gest a better plan for breaking objectives 
and destroying slides. 
These directions will enable the begin- 
ner to examine simple transparent objects, 
such as the eye, foot, tongue, etc., of a 
fly ; sections of plants and of animal tis- 
sues, etc. Very many objects cannot be 
thus examined, however ; the light cannot 
be made to pass through them, and they 
can be seen only by the light reflected 
from their surface. In this case it is al- 
most always necessary to throw a very 
intense light upon the object, particularly 
if the object-glasses are not of the very 
best kind. To condense the light upon 
the object, a condensing lens is generally 
employed. The concave mirror, however, 
answers the same purpose, provided it can 
either be detached from the microscope 
and mounted on a separate stand, or raised 
above the stage, as is now arranged even 
in many of the cheaper forms of the com- 
pound instrument. To learn the use of 
the condensing lens or mirror, let the stu- 
dent arrange these in relation to the lamp 
so as to throw a bright spot of light on the 
object. In the case of the lens, the light 
passes through it, and is brought to a 
focus on the other side, just as a boy sets 
Are to an object by means of a burning 
glass. When the mirror is used, it is 
placed beyond the object, and the rays of 
light, after striking it, are reflected back 
again upon the object. In using either 
the mirror or the lens, it will be found 
necessary to place them at a proper dis- 
tance from the lamp and from the object. 
If the lens be placed too near the lamp, 
the rays of the latter cannot be brought 
to a focus. It would be easy to give 
mathematical diagrams explaining this, 
but a few experiments will teach more 
than pages of writing. 
— Certain manufacturers of a cheap 
microscope advertise it as follows: "It 
will show the tubular structure of hair; 
also the much-talked-of trichina spiralis, 
or pork- worm, which has caused so much 
excitement and so many deaths, thus fur- 
nishing an endless source of amusement 
and instruction combined" ! ! 
