ON THE CONSTRUCTION AND USE OF THE SIMPLE KALEIDOSCOPE.
In order to construct the Kaleidoscope in its most simple form, we
must procure two reflectors, about five, six, seven, or eight inches
long. These reflectors may be either rectangular plates, or plates
shaped like those represented in Fig. 1, having their broadest ends
=A O=, =B O=, from one to two inches wide, and their narrowest ends
=_a_ E=, =_b_ E=, half an inch wide. If the reflectors are of glass,
the newest plate glass should be used, as a great deal of light is
lost by employing old plate glass, with scratches or imperfections
upon its surface. The plate glass may be either quicksilvered or not,
or its posterior surface may be ground, or covered with black wax, or
black varnish, or anything else that removes its reflective power.
This, however, is by no means absolutely necessary, for if the eye
is properly placed, the reflexions from the posterior surface will
scarcely affect the distinctness of the picture, unless in very intense
lights. If it should be thought necessary to extinguish, as completely
as possible, all extraneous light that may be thrown into the tube
from the posterior surface of the glass plates, that surface should be
coated with a varnish of the same refractive and dispersive power as
the glass.
If the plates of glass have been skilfully cut with the diamond, so as
to have their edges perfectly straight, and free from chips, two of
the edges may be placed together, as in Fig. 17 (p. 49), or one edge
of one plate may be placed against the surface of the other plate, as
shown in the section of Mr. Bates’s Kaleidoscope. But if the edges are
rough and uneven, one of them may be made quite straight, and freed
from all imperfections, by grinding it upon a flat surface, with very
fine emery, or with the powder scraped from a hone. When the two plates
are laid together, so as to form a perfect junction, they are then to
be placed in a brass or any other tube, so as to form an angle of 45°,
36°, 30°, or any even aliquot part of a circle. In order to do this
with perfect accuracy, direct the tube containing the reflectors to
any line, such as _m n_, Fig. 2, placed very obliquely to one of the
reflectors =A O=, and open or shut the plates till the figure of a star
is formed, composed of 8, 10, or 12 sectors, or with 4, 5, or 6 points,
corresponding to angles of 45°, 36°, and 30°. When all the points of
the star are equally perfect, and none of the lines which form the
salient and re-entering angles disunited, the reflectors must be fixed
in that position by small arches of brass or wood =A B=, =_a b_=, Fig.
21, filed down till they exactly fit the space between the open ends of
the plates. The plates must then be kept in this position by pieces or
wedges of cork or wood, or any other substance pushed between them and
the tube. The greatest care, however, must be taken that these wedges
press lightly upon the reflectors, for a very slight force is capable
of bending and altering the figure even of very thick plates of glass.
When the reflectors are thus placed in the tube, as in Fig. 21, their
extremities =_a_ E=, =_b_ E=, next the eye, must reach to the very end
of the tube, as it is of the greatest importance that the eye get as
near as possible to the reflectors. The other ends of the reflectors
=A O=, =B O=, must also extend to the other extremity of the tube, in
order that they may be brought into contact with the objects which are
to be applied to the instrument. In using transparent objects the cell
or box which contains them may be screwed into the end of the tube, so
as to reach the ends of the reflectors, if they happen to terminate
within the tube; but an instrument thus constructed is incapable of
being applied to opaque objects, or to transparent objects seen by
reflected light.
[Illustration: FIG. 21.]
If the plates are narrower at the eye-end, as in Fig. 21, the angular
point =E= should be a little on one side of the axis of the tube, in
order that the aperture in the centre of the brass cap next the eye
may be brought as near as possible to =E=. When the plates have the
same breadth at both ends, the angular point =E= will be near the
lower circumference of the tube, as it is at =O=; and in this case it
is necessary to place the eye-hole out of the centre, so as to be a
little above the angular point =E=. This construction is less elegant
than the preceding; but it has the advantage of giving more room for
the introduction of a feather, or a piece of thin wood covered with
leather, for the purpose of removing the dust which is constantly
accumulating between the reflectors. In some instances the plates have
been put together in such a manner that they may be taken out of the
tube, for the purpose of being cleaned; but though this construction
has its advantages, yet it requires some ingenuity to replace the
reflectors with facility, and to fix them at the exact inclination
which is required. One of the most convenient methods is to support the
reflector in a groove cut out of a solid cylinder of dry wood of nearly
the same diameter as the tube; and after a slip of wood, or any other
substance, is placed along the open edges of the plates, to keep them
at the proper angle given by the groove, the whole is slipped into the
tube, where it remains firm and secure from all accident.
If the length of the reflectors is less than the shortest distance at
which the eye is capable of seeing objects with perfect distinctness,
it will be necessary to place at the eye-end =E= a convex lens, whose
focal length is equal to, or an inch or two greater than, the length
of the reflectors. By this means the observer will see with perfect
distinctness the objects placed at the object end of the Kaleidoscope.
This lens, however, must be removed when the instrument is to be used
by persons who are short-sighted.
The proper application of the objects at the end of the reflectors
is now the only step which is required to complete the simple
Kaleidoscope. The method of forming, selecting, and mixing the objects,
will be described in the next chapter. At present, we shall confine our
attention to the various methods which may be employed in applying them
to the end of the reflectors.
[Illustration: FIG. 22.]
The first and most simple method consists in bringing the tube about
half an inch beyond the ends of the reflectors. A circular piece of
thin plane glass of the same diameter as the tube, is then pushed into
the tube, so as to touch the reflectors. The pieces of coloured glass
being laid upon this piece of glass when the tube is held in a vertical
position, another similar disc of plane glass, having its outer surface
ground with fine emery, is next placed above the glass fragments, being
prevented from pressing upon them, or approaching too near the first
plane glass by a ring of copper or brass; and is kept in its place
by burnishing down the end of the tube. The eye being placed at the
other end of the instrument, the observer turns the whole round in
his hand, and perceives an infinite variety of beautiful figures and
patterns, in consequence of the succession of new fragments, which are
brought opposite the aperture by their own gravity, and by the rotatory
motion of the tube. In this rude state, however, the instrument is by
no means susceptible of affording very pleasing exhibitions. A very
disagreeable effect is produced by bringing the darkest sectors, or
those formed by the greatest number of reflexions, to the upper part
of the circular field, and though the variety of patterns will be very
great, yet the instrument is limited to the same series of fragments,
and cannot be applied to the numerous objects which are perpetually
presenting themselves to our notice. These evils can be removed only
by adopting the construction shown in Fig. 22, in which the reflectors
reach the very end of the tube. Upon the end of the tube _a b_, _c
d_, Fig. 22, is placed a ring of brass, _m n_, which moves easily upon
the tube _a b c d_, and is kept in its place by a shoulder of brass
on each side of it. A brass cell, =M N=, is then made to slip tightly
upon the moveable ring _m n_, so that when the cell is turned round by
means of the milled end at =M N=, the ring _m n_ may move freely upon
the tube. The fragments of coloured glass, etc., are now placed in a
small object-box, as it may be called, consisting of two glasses, the
innermost of which, _m n_, is transparent, and the other ground on
the outside =P=, and kept at the distance of ⅛th or ⅒th of an inch by
a brass rim: this brass rim generally consists of two pieces, which
screw into one another, so that the object-plate can be opened by
unscrewing it, and the fragments changed at pleasure. This object-box
is placed at the bottom of the cell =M N=, as shown at =O P=, and the
depth of the cell is such as to allow the side =O= to touch the end
of the reflectors, when the cell is slipped upon the ring _m n_. When
this is done, the instrument is held in one hand with the angular point
=E=, Fig. 21, downwards, which is known by a mark on the upper side
of the tube between _a_ and _b_, and the cell is turned round with
the other hand, so as to present different fragments of the included
glass before the aperture =A O B=. The tube may be directed to the
brightest part of the sky in the day-time, or in the evening to a
candle, or an Argand Lamp, so as to transmit the light directly through
the coloured fragments; but it will always be found to give richer and
more brilliant effects if the tube is directed to the window-shutter,
a little to one side of the light, or is held to one side of the
candle—or, what is still better, between two candles or lamps placed
as near each other as possible. In this way the picture created by the
instrument is not composed of the harsh tints formed by transmitted
light; but of the various reflected and softened colours which are
thrown into the tube from the sides and angles of the glass fragments.
When the pattern remains fixed in any position of the instrument, a
variety of beautiful changes may be effected by making the end of the
tube revolve round a candle or a bright gas flame, placed near the
object-plate. The general pattern remains the same, but its colours
vary both in their position and intensity, as the light falls upon
different sides of the fragments of glass.
In the preceding method of applying the objects to the reflectors,
the fragments of coloured glass are introduced before the aperture,
and pass across it in concentric circles; and as the fragments always
descend by their own gravity, the changes in the picture, though
infinite in number, constantly take place in a similar manner. This
defect may be remedied, and a great degree of variety exhibited in
the motion of the fragments, by making the object-plates rectangular
instead of circular, and moving them through a groove cut in the cell
at =M N=, in the same manner as is done with the pictures or sliders
for the magic lantern and solar microscope. By this means the different
fragments that present themselves to the aperture may be made to pass
across it in every possible direction, and very interesting effects may
be produced by a combination of the rotatory and rectilineal motions of
the object-plate. When the object or objects are fixed, and the tube
with the reflectors moved round a centre, as described in Chapter
II.,[3] we have the same succession of symmetrical pictures; but in
this case every alternate sector is stationary, and the same number in
motion, the moving figures always changing their form, and assuming
that of the figures in the stationary sectors, which of course change,
while the ends of the mirror pass over the fixed objects.
[3] See Chapter X.
When the simple Kaleidoscope is applied to opaque objects, such as a
seal, a watch-chain, the seconds hands of a watch, coins, pictures,
gems, shells, flowers, leaves, and petals of plants, impressions
from seals, etc., the object, instead of being held between the eye
and the light, must be viewed in the same manner as we view objects
through a microscope, being always placed as near the instrument as
possible, and so as to allow the light to fall freely upon the object.
The object-plates, and all transparent objects, may be viewed in this
manner; but the most splendid exhibition of this kind is to view minute
fragments of coloured glass, and objects with opaque colours, etc.,
placed in a flat box, the bottom of which is made of mirror-glass. The
light reflected from the mirror-glass, and transmitted through the
transparent fragments, is combined with the light reflected both from
the transparent and opaque fragments, and forms an effect of the finest
kind.
As dust is apt to collect in the angle formed by the reflectors, it may
be removed when the reflectors are fixed, either by the end of a strong
feather, or blown away with a pair of bellows. When the dust is lodged
upon the face of the reflectors, it should be removed by a piece of
soft leather.