If you can, get the maker himself to show
you the special mode of handling the instrument
you select. Generally, the thing to be
viewed, on a slip of glass, is held down on
the stage by springs, or is slipped through
grooves, something like the painted slides of
a magic lantern. In order that it should be
clearly seen, the instrument must be brought
to its exact focus (the Latin word for fireplace),
or the point where the converging and
concentrated rays meet, and which is, in fact,
the point at which a burning-glass becomes
incendiary. First, the approximate or rough
focus is found, either by slipping the instrument
through a sort of telescope tube, or by
a rack-work; and then the very precise point
is hit upon by turning a fine adjustment or
micrometer screw. By pushing the slide or
port-object backward and forward with the
thumbs of each hand, the object is examined
in its breadth and length; by turning the
micrometer screw, in its depth and thickness.
For, with a high power, you cannot see the
whole of a single globule at once; an almost
insensible turn of the screw brings a fresh
portion of the object within the focus. But
these little manipulations are not acquired
without a fatiguing amount of practice, even
though the image seen is reversed; that is,
to make it go to the right, you must push
the object-slide to the left, and to move it
apparently upward you must direct your
gentle touches downward.

Next, as to microscopic books. It is a good
plan, when you want to comprehend a
subject, to get together all the works that treat
of it. On looking them through, the repetitions
and the chaff are sifted away without
much exertion of intellect, and you are then
possessed of all the solid grain. Three modern
works are so good, and so wonderfully cheap,
that the young microscopist will assuredly
purchase the entire trio: The Microscope and
its Revelations, by Dr. Carpenter, with three
hundred and fifty woodcuts; The Microscope,
its History, Construction, and Applications,
by Jabez Hogg, M.R.C.S., with upwards of
five hundred engravings; and The Microscope,
by Dr. Lardner, with a hundred and
forty-seven engravings. The utility of the
last work is much diminished by the want of
an index, and still more by the affectation,
after Cobbett, of not being paged; the only
guide to its valuable contents are figures
which refer to paragraphs. Quekett on
the Microscope, Pritchard's Microscopic
Cabinet, and Of Microscopes, and the
Discoveries made thereby, by Henry Baker, may
be profitably consulted. For physiological
students, the works of Dr. Robin (in French)
and of Dr. Hassell are of the highest interest.

But a microscope, and a library in alliance
with it, alone, without plenty of objects to
look at, are a theatre with its repertory of
plays, but wanting scenery and actors. It
is the opera-house and its accumulated
scores, minus the fiddlers, the singers, and
the dancers. Microscopists, therefore, must
provide themselves both with living
performers and inanimate decorations. Happily
our artists do not ask the salaries of Piccolomini,
or Rosati, and are content to wait the
call-boy's summons in a green-room of quite
modest dimensions and furniture. One or
two shelves, filled with bottles, boxes, and
pots, will serve as the menagerie for an
innumerable company of first-rate performers,
whose talents are unrivalled in their respective
lines of parts. Thus, one of the celebrities
who was among the first to make his
appearance on the microscopic stage—the
paste-eel—is open to an engagement at any
period of the year. Simply take note that
the paste proper for procuring the animalcules
called eels, is made with flour and water
only—that of the shops, containing resin and
other matters, being unfit for the purpose.
It must be made very thick, and well boiled;
when cold, it should be beaten and thoroughly
stirred with a wooden spatula. This must
be repeated every day, to prevent mildew on
its surface; previously examining a portion
with a magnifier, to ascertain whether it
contains any eels. If the weather be warm, a
few days will suffice to produce them. When
they are once obtained, their motion on the
surface of the paste will prevent any mouldy
growth, and it, therefore, requires no further
attention. If the paste be too thin, the eels
will creep up the sides of the paste-pot. In
this case, a portion of very thick paste must
be added, to preserve them. But the fresh
supply must not be put upon them. They must
be placed upon it. When you require her
Majesty's servants in little to exhibit their
graces, take a few drops of clean water, and
put a small portion of the paste containing
the eels into it. The water serves them as
their bath and their dressing-room; after
they have remained therein a minute or two,
they may be taken out, and placed under
the microscope, when the first act of the
comedy will begin. Their versatility of talent
enables them to play even minor parts in
tragedy. They are a favourite prey of many
aquatic larvæ. When the latter are starring
upon your boards, put in a few supernumerary
eels; they will be devoured without
mercy, and will add much to the interest of
the spectacle. You will have tableaux not
inferior to those presented by the terrier
Billy in his grand feat of killing a hundred
rats in fifty seconds.

Paste-eels are still a mystery in their nature;
they propagate only by bringing forth their
young alive, as far as is known. How, then,
do they come in the paste? if they lay no eggs,
none can be floating about in the air. The
boiling, one would think, must destroy any
germs of life contained in the flour, or the
water of which the paste is made. Most
philosophers are afraid of admitting what
is called spontaneous generation. It is not
very clear why they fear it, since the admission