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74 MODERN MAGIC LANTERNS.
is, if the screen has the position indicated by one or other of
the dotted lines, the pictures thrown upon it will be distorted.
It will be seen from this that if the lantern is tipped
up or down the screen must not be vertical. The same remarks
apply with equal force to the turning of the lantern
to one side or the other.
Having seen about this, the lantern can be lit up, when,
if limelight is to be used, the light will have to be centred,
that is, adjusted until the brightest part of the lime is in
the axis of the lantern, and is also at the focus of the
condenser. (Oil lamps are not provided with a means of
centering the light, as its position is invariable, and is or
Fig. 59. PHOTOGRAPHS OF THE SCREEN WITH
THE JET IN AND OUT OF POSITION.
should be adjusted by the maker.) To do this, the jet having
been lit and the oxygen turned on, a slide must be put into
the lantern, and disregarding for the moment whether its
illumination is even or not, focussed upon the screen, after
which it can be taken out without disturbing the focussing.
The chances are that the circle of light upon the sheet will
now resemble either A, B, C, D, or E, Fig. 59, which indicate
respectively that the light is too high (A), too low (3), too
much to the right (c), or to the left (c). This must be corrected
by slackening the screw which holds the jet in position
on the tray pin, and finally clamping it again when the disc
presents the appearance denoted by E. When this is the
THE MANIPULATION OF THE LANTERN. 75
case, the light is centred, and must then be adjusted as
regards its distance from the condenser. This is done by
sliding tray and all in the grooves of the lantern until the
disc is evenly and brightly illuminated all over (F) ; the
correct position is easily found. The carrier should then be
adjusted so that its opening occupies the centre of this disc,
and if it can be clamped in that position when found, so
much the better. This being done, it is useful to put a slide
once more into the carrier, and with the rack and pinion
motion of the lens midway, i.e., neither fully in nor fully
out, to focus it with the sliding adjustment only. If this is
not done, it may be found that it is impossible to focus
each slide sharply with the rack and pinion because it is at
the end of its travel.
The slides demand the next attention. If practicable it
will be found an excellent plan to tie them up in a paper
parcel and put them in a warm oven for a little while. If
this cannot be done they may be warmed by being placed
in an open grooved box before the fire, or even allowed to
remain, separated, in a warm room for a little while. Unless
this is done, there will be a great likelihood in the intense
heat of the limelight or electric light of the deposition of
moisture on the cold slide when put into the lantern. The
slides when this is the case are said to "sweat," it is painfully
obvious on the screen, and will spoil completely an
exhibition which is in all other respects first-class.
The slides must be arranged in the order in which they
are required. For this purpose they are often kept in
grooved boxes, but this way may lead to mistakes. The
most careful lanternist may have his attention distracted
for a moment, and in the obscurity may take a slide from
any part of the box instead of the next in order, and so get
them disarranged and make one of those slight but annoying
hitches which mar what should be the regularity which leads
to success. For this reason we prefer to have the slides
piled up in stacks of about thirty, only one of which shall be
within reach at a time, there is then no possibility that any
slide but the next in order can be picked up by accident.
Another important detail is the proper marking of the
slides. There has been for many years every possible