between a genuine signature and an imitation or forgery of the
same. For this purpose, there was brought into court a powerful
reflecting magic lantern. The room was darkened, and images of the
two signatures, enormously magnified, were thrown side by side upon
a screen before the judge and jury. The false signature was at once
revealed. The illumination of the writing was effected by means of
two powerful lime-lights contained within the lantern. The peculiar
arrangement of the lights and screen enables the examiner to discover
the surface of the paper through the ink, so that patching, shading,
or painting of letters becomes evident the instant it is brought
under the focus of the lantern. An arrangement of screens, by which
the light is cut off alternately from either side of the instrument,
discovers any tampering with the surface of the paper, either by
scratching or washing by chemicals. (In other words, by throwing the
light alternately from either side, the relief caused by the grain of
the paper is clearly shown; and any tampering with that relief, by
scratching or otherwise, at once becomes apparent.) The instrument, in
this case, was of sufficient capacity to view at once two bank-notes
placed side by side, and the pictures were of such fineness that there
was no difficulty in viewing their smallest details. I fear that the
introduction of a magic lantern into an English court of law would be
rather too sensational for the ordinary legal mind--particularly as the
evidence of an expert, with the help of a microscope, would answer the
same end.
Under the name of the Physioscope, an immense opaque lantern was
exhibited some years back in London. The object magnified on the
sheet was the human face, and a correcting lens was included in the
apparatus, so that the face was seen right way up. It was always rather
an unhappy face, for the individual who lent his countenance to the
transaction had on either side of him, and within a few inches of his
cheeks, a very powerful lime-light, the heat and glare from which were
sufficient to render anyone uncomfortable who was not a salamander.
THE LANTERN MICROSCOPE.
Of late years it has become possible to take very beautiful photographs
of microscopic objects, which, when used as lantern-slides, give a very
fine effect. Numerous slides of this character may now be purchased,
which cover a vast field of microscopic knowledge, and many will be
content with what they can thus obtain. But there is another class
of workers who, perhaps possessing a large number of microscopic
slides, will be glad to utilize them for the lantern, so that they
are no longer limited to the individual eye. For these the lantern
microscope, which will screw in front of the lantern in place of the
usual optical system, is a most useful instrument. Different makers
advertise in their catalogues lantern microscopes which range in
price from twenty-five shillings to as many guineas. And it recently
came to my knowledge that a well-known London optician has undertaken
the construction of a few of these instruments at the price of £150
each. The amateur lanternist will, therefore, have some difficulty in
deciding what he ought to pay for such an instrument. And it is most
difficult to advise him on that point. His best plan is, perhaps, to
see for himself what the makers can offer him, and, if possible, to
seek a trial of the instrument before he purchases it.
The lantern microscope is a modification of the old solar
microscope--an instrument which could be screwed against a hole
in the shutter of a darkened room--and which had a mirror outside
which projected a beam of sunlight through it. The objective lenses
were uncorrected, and small in aperture, so that the instrument was
far from being a perfect one. But the intensity of the solar light
covered many objectionable features, and it was possible to get
some astonishing effects with the contrivance. But sunlight is such
an uncertain commodity in our climate that, when the lime-light came
into prominence, the old solar microscope was forgotten in favour of
that which depended upon a more constant, if a far less intense, light
source.
The great difficulty to overcome in the lantern microscope is to get
the light sufficiently intense to well illuminate the objects. The
aperture of a microscope objective, even of low power, is so small,
that, when the pencil of light which it emits is spread over a screen,
the light is so attenuated that the details of the object are difficult
to make out. In the near future, when we are promised that electricity
shall be laid on to our homes, as gas is now supplied to us, the
difficulty will disappear, for the electric-arc light is many times
more intense than the most powerful lime-jet.
Having obtained a lantern microscope, the next thing to consider is the
class of objects which can best be shown with it. To help the reader in
determining this point, I will now give a kind of sketch of a popular
lecture to accompany an exhibition of the instrument.
Such a lecture might usefully commence with a brief description of
the microscope: its history, and how, in its improved form, it has
opened up a world of minute life, of which our forefathers could have
had no conception. We might then put forward a few remarks as to the
adaptation of the microscope to the oxyhydrogen lantern, and point out
how by its aid a number of persons can at the same time see what, in an
ordinary microscope, is visible to only one person. So much by way of
introduction.
We might next enlarge upon the circumstance that the contents of the
world have been classified into three general divisions--popularly
known as the three kingdoms of Nature: the Mineral Kingdom, the
Vegetable Kingdom, and the Animal Kingdom. Show how one is dependent
upon the other, and the difficulty in many cases of drawing a line to
separate the minute organisms of the Animal Kingdom from those of the
Vegetable World. Numerous examples from the lower forms of life may be
quoted to illustrate this. Now show and explain subjects from each of
the three divisions, taking the minerals first. Define a mineral, and
show how they crystallize in definite forms. Illustrate the process
of crystallization by putting a drop of a saturated solution of
sal-ammoniac on a slip of glass, and spreading it over with a brush.
Such a glass placed in the microscope will, as it dries, become covered
with branches of crystals, which seem to grow and strike out in various
directions on the sheet in a truly marvellous manner. Sections of
various minerals may next be shown, finishing with sections of coal. In
pointing out the origin of coal from plants, we may easily drift into
the next division of our subject--the Vegetable Kingdom.
Here we have indeed a wide field to illustrate. Commencing from the
simple cell, as exhibited, for instance, in a bit of so-called green
mould, and arriving gradually at sections of different stems of plants
(which by the way form most beautiful objects on the screen), sections
of different woods, parts of flowers, etc. From these it will be easy
to step over the indistinct boundary-line which separates us from the
Animal World. Here we can commence with the lowest organisms; next
show the living inhabitants of our ponds and ditches. Arrive at the
Insect World, and show the generally unfamiliar parts of familiar
insects--bees, wasps, flies, etc. We can then go higher, and exhibit
sections of bone, hair, etc.; finishing with the structure of the human
body, so far as it can be indicated by means of the microscope. This
is a brief sketch of the kind of entertainment the microscope is able
to afford, which can be modified to suit the views of the exhibitor.
MECHANICAL OR MOVING-PICTURES.
The most common form of moveable slide is that known as a ‘comic slip.’
This mechanical contrivance for the amusement of youth is generally of
the coarsest execution, and it speaks little for the originality of our
slide-producers that the same old things should appear in catalogues
year after year with no improvement. The ‘comic slip’ consists of
a glass in a wooden frame, with another loose piece of glass which
can work backwards and forwards in front of it. This movable glass
generally serves as a mere screen to cover something painted underneath
it, and it is rubbed over with black varnish so as to be opaque. Thus
a gentleman is represented with a nose of the normal size, but as the
screen is withdrawn it elongates to an awful extent. Or a woman’s
tongue may be graphically, if not elegantly, portrayed in the same
manner.
In another class of slide a circular glass is kept in slow rotation
in front of the slide proper by means of a rack-work attachment. A
common design for this device is a landscape with a windmill in the
centre. The sails of the mill are painted on the revolving glass, and
can be kept in rotation as long as desired. The chromatrope effect
is managed in the same way, only that in this case both glasses are
caused to slowly revolve in reverse directions. There are many people
who admire chromatropes, and many others who regard them as rather
trying to the eyes. Rippling water, the rising or setting of the sun
or moon, and astronomical slides illustrative of the movements of the
heavenly bodies, are among the subjects which can be well illustrated
by mechanical means.
Perhaps the cleverest piece of apparatus ever invented to give
the effect of movement by means of a magic lantern is Beale’s
choreutoscope. This instrument depends upon the well-known phenomenon
common to our eyes, called persistence of vision. The image of anything
that we look at is cast upon the retina at the back of the eye by the
agency of the crystalline lens, which is placed behind the pupil.
So far, the human eye resembles a camera obscura. Persistence of
vision means that an image so cast upon the retina remains impressed
there for about the eighth part of a second. For this reason we wink
continually without knowing it, for the light impression remains with
us during the short time that the eye is closed in accomplishing that
necessary action. A burnt stick with a red-hot end whirled round and
round appears to us like an unbroken circle of fire. The separate drops
of rain as they fall from the sky look like streaks of water, and so
an artist will represent them in his picture. A quickly moving meteor
looks like a long trail of fire for the same reason.
In the choreutoscope we have a very elegant adaptation of the same
principle. It consists, in its commercial form, of a slide arrangement
that can be placed in any lantern. This contains a narrow strip of
glass, with, say, six figures painted upon it, each figure having a
different position. A dancing man is a good representative of the rest.
By a turn of a handle each figure is brought into view successively,
but so rapidly as to give the effect of moving arms and legs. An
interceptor or screen runs in front of each figure as the change occurs.
One of the best designs made for this instrument is a dancing skeleton
(see annexed cut). In this case the figures are cut stencil-fashion
out of very thin brass, and the openings thus cut transmit so much
light that the effect is far more brilliant than if the design were
executed on glass in the usual manner. The choreutoscope is not only a
most amusing contrivance, but it illustrates in a very beautiful manner
this optical law called ‘persistence of vision.’
[Illustration: FIG. 9. Facsimile of a dancing skeleton for Beale’s
Choreutoscope.]
CONCLUDING REMARKS.
The best lantern and the best pictures will not interest an audience
unless the entertainer or lecturer is up to his work, and the matter
which he conveys is skilfully put together. I believe that lecturing
would be far more popular among us had it not been for the numbers
of utterly incompetent men who have in past years bored audiences to
such an extent that the word ‘lecture’ is to them as a red rag is to a
bull. When I say incompetent men, I do not mean uneducated ones; but I
mean those who from natural want of voice, and utter ignorance of its
management, are generally unfit for public speaking. It seems to be too
often conceded that because a man has written a book--or done something
else which has brought him before public notice--he is, without any
previous knowledge or practice, fit to lecture on the particular
subject with which his name is identified. Or his claims to recognition
as a lecturer are based upon certain cabalistic letters after his name,
which in many cases represent only so many guineas yearly subscribed to
those who confer them. Lecturing is an art that can only be acquired
successfully by those who have certain qualifications for the work,
and among these the foremost is the power of imparting knowledge to
others in a common-sense and interesting manner. Luckily for him, the
amateur lecturer is likely to meet with a far more indulgent audience
than those which professional men have occasionally to face; but this
is no reason why he should be careless as to his method of delivery,
or of the matter delivered. Perhaps the er--worst fault er--which a
lecturer can er--fall into--is the one indicated er--in this sentence.
‘To _err_ is human,’ in a wider sense, unfortunately, than Pope, the
writer of that well-known line, ever dreamt of. Unless a would-be
lecturer can conquer this tiresome habit, or any other trick of speech
which he may have cultivated, by all means let him confine himself to
the management of the lantern while some one else acts as showman.
If two people are thus managing an exhibition between them, and if
the room be large, so that they are widely separated, some signal
from the lecturer to indicate that he wants the next picture thrown
on the screen becomes necessary. A bell, or anything that makes a
noise, is distracting both to lecturer and audience. Still worse are
verbal instructions from one to the other. I myself use an electric
single-stroke bell with the gong removed, the hammer of which gives
a little click unmistakable to the operator, but quite unheard by the
audience. Such a bell can be placed close to the lantern, while its
push is far away on the lecturer’s desk. Sometimes a string can be
carried from lecturer to operator, a gentle pull of which will give the
necessary signal. Some lecturers signal by uncovering a little pane
of red glass in the back of their reading-lamp. But I think that any
sight signal is inadmissible, because the operator has quite enough
to do in attending to his duties without having his attention thus
distracted. The signal, of whatever nature it be, should be given by
the lecturer some seconds before he has finished with the picture in
hand, otherwise there is an awkward pause while the operator makes the
necessary change. Before the lecture begins, the reader should make
himself not only thoroughly familiar with his subject, but should be
also familiar with the different pictures which illustrate it. And this
especially applies to the common case of those who have purchased or
hired a set of slides and a published lantern reading--many of which
are compiled by writers of repute, and are in every way excellent. Let
him, then, carefully go through the reading beforehand, comparing each
picture with the text, and making himself so familiar with its details
that he is afterwards able, during performance, to point out anything
to which attention may advantageously be directed. Particularly is
this necessary in the case of an introductory map, where places of
importance to the subject in hand must be pointed out. The most
convenient form of pointer, by the way, is a Japanese fishing-rod,
which telescopes into small compass when not in use.
For an evening’s lantern entertainment to be successful, a great deal
depends upon the operator. With a mineral-oil lamp in a small room, his
duties are not very onerous, for the lamp when once established should
require no further attention, except it be to turn down a wick which
shows symptoms of smoking. But he should be careful to have in reserve
a glass or two to replace the front glass of the combustion-chamber,
which may crack through some unexpected draught of air. His slides must
all be numbered and in order. They may be each mounted in a wooden
frame to fit the lantern stage, or else the lantern may be fitted
with a permanent grooved slide in which the glass pictures are placed
one after another, the last one pushing out the one before. Another
plan, which is a good one to adopt where a single lantern only is
being used, is to make use of what is called a panoramic slide. It is
constructed like the one just described, only it is furnished with a
travelling tape upon which each picture rests. The turn of a handle
moves the tape, and the pictures travel forward panorama-fashion.
In the use of a double lantern furnished with lime-jets, there is
plenty for two hands to do, for the operator has to keep his attention
fixed not only upon the business of changing the pictures, but upon the
condition of the lights. As the pressure of the oxygen gas varies as it
is gradually consumed, so the supply of the two gases to the jets will
want constant adjustment if the maximum quantity of light is expected.
Extra weights, too, must be added as the pressure-boards gradually sink
down. Beyond carefulness in this respect, the lantern operator must see
to the occasional turning of his limes, taking care to do this when
the lime wanting attention is not in actual use. He should also find
time to wipe the glass of each picture with a leather before putting
it in the lantern, for a film of moisture condenses on the surface,
particularly in a room full of people.
The success of a lantern entertainment depends nearly as much on the
competence of the assistant as it does on the powers of the lecturer.
I am perhaps fastidious on this point, for my lecturing apprenticeship
was served at the late Royal Polytechnic Institution, where operators
were employed who had spent the best part of their lives in this
particular work. It was seldom, indeed, that they made a mistake.
THE END.
BILLING AND SONS, PRINTERS, GUILDFORD.
Transcriber's Notes:
Italics are shown thus: _sloping_.
Variations in spelling and hyphenation are retained.
Perceived typographical errors have been changed.