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88 MODERN MAGIC LANTERNS.
appertaining to a lantern by some long Greek name, are often
called Aphengescopes. It is a useful device occasionally for
demonstration purposes, but owing to the very great loss
of light, can only be employed with limelight or with the
electric arc, and then is never very satisfactory. In Fig. 65
the source of light is shown at B, and the condensers at
c c, the object, which is placed at n, having its imago
focussed upon the screen by means of the objective, E.
There is no need to get a special lantern for the purpose,
as a box is easily arranged to carry the objective at one end
and to receive the nozzle of the lantern in the direction
shown. Such a box should have its interior lined with black
paper, or better, with black velvet. The back can be arranged
to carry the objects it is desired to exhibit, access
being obtained by the side A, which is closed with a curtain.
When the Aphengescope is being used, and, indeed, in a
large number of other cases, it will be found that, unless
steps are taken to prevent it, harm will very frequently occur
from delicate instruments or inflammable substances being
exposed to the intense heat concentrated upon them by the
condenser. To obviate this, what is known as an alum cell
is employed. This is an arrangement similar to that shown
in Fig. 61; in fact, the same cell can be employed for
either purpose, as required. It is filled with a cold saturated
solution of alum, which must have been carefully filtered so
as to be quite free from dust or other floating particles. The
solution will in course of time get fairly hot, but while allowing
nearly all the light to pass, it will absorb the heat, which
would otherwise be doing harm. In the absence of the alum
solution, plain water can be employed. It is not quite so
efficient, but is satisfactory enough for most purposes.
Another arrangement of the lantern for demonstration
purposes is that shown in Fig. 66, which shows the method
of making vertical projections, as they are called. The
beam of light from A, as it leaves the condenser, B, falls
upon a mirror, F F, placed at an angle of 45 degrees
with the horizontal, from which it is reflected vertically
upwards. The table, n D, upon which the object to be
projected is placed, is immediately over the mirror, while
above it is placed the objective, E, bearing above it again a
LANTERN EXPERIMENTS.
reflector, G, which once more directs the beam in a horizontal
direction to the screen. For most purposes such
an arrangement can be fixed up at very little expense to
answer all requirements except where great brilliancy and
crispness of definition is desired. The bottom mirror can be
a piece of the usual silvered plate glass, the top one is best
of the thinnest silvered glass procurable, as if not, the
Fig. 66.
ARRANGEMENT OF LANTERN FOR VERTICAL PROTECTIONS.
secondary reflection, that from the surface of the glass itself,
may become troublesome. It will be seen that the two
component lenses of the condenser have to be separated, one
remaining in the usual position in front of the illuminant,
and the other immediately beneath the table carrying the object
to be projected. With this arrangement of the apparatus
many experiments, such as those showing crystallisation,
etc., can be performed. For this purpose a glass dish with
an even flat bottom is required. This is placed upon the
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