d of the said tube contains the eye-piece, so named because by
its aid the eye is allowed to receive the image duly focussed and
enlarged.

As a rule, beginners work with one objective only, generally a one inch.

Image: FIG. 6.--Microscope in position for drawing objects.

A much higher power than this is necessary if the fibre in question is
to be seen at its best, and for the purpose of this chapter a quarter
inch objective will be used.

Underneath the stage, which is pierced by a circular aperture, is a
diaphragm. This regulates the quantity of light which is to be
transmitted by means of the silvered reflector shown in the
illustration.

As a rule, two reflectors are fixed in the same holder; one a concave
mirror, the other a plane one. The former brings the rays of light to a
point or focus while the latter simply passes the beam of light along
just as it received it, viz., as a parallel beam of light.

In examining fibres the concave mirror will be of most use. An ordinary
lamp is usually good enough for the light required, the one figured
being very suitable and having a tube-like arrangement of wick. Behind
the body-tube are two forms of adjustment, coarse and fine. The latter
is worked by means of the milled screw, conical in shape, which is found
immediately behind the coarse adjustment. The operator is supposed to
have had some slight experience in the manipulation of the microscope.
The slide is now placed upon the stage. Fine Sea Islands cotton is
mounted in Canada Balsam and protected by a small circular cover glass.

Now rack down the body-tube by means of the coarse adjustment until
within 1/16 of an inch of the cover-glass of the slide. Now see that the
light from the lamp is fully on the cotton strands. Rack up or down, as
the case may be, with the fine adjustment, and a wonderful sight meets
the eye, for the cotton viewed through the microscope is altogether
unlike what we should expect it to be.

Running completely across the field are a number of strands, varying in
thickness, form and natural twist. What is meant by natural twist is
very clearly shown in Fig. 7.

Most people have seen india-rubber tubing or piping such as is used in
the chemical laboratory or that often found attached to feeding bottles.
Take about a foot of this and hold one end firmly. Abstract the air by
means of the mouth, and it will be found that immediately the air is
taken out the tube collapses. Now if the rubb