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52 MODERN MAGIC LANTERNS. THE LANTERN BODY. 53
back by which to introduce the illuminant, and a curtain
should hang loosely round the back of the lantern, and
cut off the stray light which would otherwise escape
thence into the room. The doors usually are provided
with a little window glazed with red or blue glass, so
that the working of the lamp can be observed. These
windows are not of much use, most operators preferring
to look at the naked light itself, but they might be made
more suitable by being both larger and glazed with, say, a
deep red and blue, or a very dark neutral-tinted glass. This
becomes a necessity with the arc lamp, which cannot be
watched through the usual windows at all. With the arc
lamp care must be used that at no time either carbon
holder or other part conveying current is brought into
contact with the metal lining of the lantern body.
The base of the lantern is best a perfectly flat board, with
an arrangement such as that shown in Fig 40, by which
the entire apparatus can be tilted up or down. The base
should be stood for
use upon an equally
flat surface, bearing
in mind that the
slightest motion of
Fig. 40. TILTING STAND FOR THE LANTERN.
the lantern will be
enormously magnified
upon the screen.
The holes by which air is admitted to the lantern are best
placed at the bottom of each side, and with oil lamps
especially should be of ample size, and must be seen to be
perfectly free. Nothing helps so much to keep a lantern
cool and in the best working order as a regular and ample
current of air passing right up through it, but not a draught
or irregular one which may endanger the condenser.
For all ordinary purposes a single lantern is sufficient.
It is much the easiest to work, has less to get out of order,
and is less expensive both in prime cost and in working.
For photographic slides, for enlarging, and for scientific
demonstrations it is all that is required. When, however, that
gradual melting of one picture into another known as
dissolving is desired, two lanterns, which when placed one
above the other are known as a binnial (Fig 41), are necessary.
The dissolving is effected with limelight by turning one
jet down and the other up, with lamps, by moving a notched
screen be1or3 one of the lanterns and simultaneously remov-
Fig. 41. A B1UNIAL LANTERN.
ing a similar screen from the other ; as shown in Fig. 42, A A
being the objectives of the two lanterns. For what are
called effects, in which sunlight fades into moonlight, buildings
are illuminated, curtains roll up or down to display or
cover up the picture, and similar things, two, and often three
lanterns are employed, the latter being known as a triunial.
Much work is often lavished on these structures, in the
shape of bright brass rods and fittings, rendering them most
costly luxuries ; but essentially they should consist of three
lanterns, each possessing in itself the most desirable features
of an efficient single lantern, the only really necessary extra