nzole.
It is used for mounting microscopic objects in, and can be got from any
optician's. It should be quite fluid. Get a large wide-mouthed bottle
and pour the balsam and benzole into it. Then add to it as much again
pure benzole. It should now be nearly as fluid as water. This is your
varnish. Apply it just as a photographer coats his glass plate with
collodion. That is done in this manner. Take hold of the slide by one
corner and pour on to it a sufficient quantity of the balsam and benzole
to cover it.

You may need to encourage it to flow by slightly tilting the slide, and
sometimes it may even be needful to take a clean quill toothpick and
direct it into some corners that otherwise would be missed. Then pour
back all the superfluous varnish into the bottle from one corner of the
slide; the varnish remaining will rapidly harden, as the benzole
evaporates quickly, and the hardening may be hastened by applying a
little heat, but while hardening the slides should be protected from
dust.

[Illustration: FIG. 2.]

I make mine perfectly hard by baking them on a thin iron plate fixed a
few inches above a small spirit lamp, but you need to take care not to
make the slides too hot, or they may crack. I can easily varnish and
harden a dozen slides in less than an hour.

A thin plate of iron, such as is used for an oven plate, can be arranged
on blocks of wood, a sufficient height over the spirit lamp. One coat of
this varnish is usually sufficient to render the slides perfectly
transparent, but a second coat can be applied as soon as the first is
hard if necessary.

The slides are now finished, but the varnished surface will easily
scratch, and must be protected by a piece of clean glass. Between the
glasses a thin paper mount should be laid, which may be a circle, an
oval, or a square, according to which is most suitable to the pictures,
and then the two glasses must be fastened together by narrow slips of
paper gummed round the edge. These mounts, and slips of paper ready
gummed, can be procured from any optician, and will save labor,
especially in fixing up the edges.

Before you join the glasses together insert at the right hand top corner
a number, so that by looking at this number you can readily arrange the
pictures in their proper sequence, and also tell which is the right side
up when putting them into the lantern carrier.

Sometimes you may wish to copy some other slides, but owing to their
having the