No invention, on being first brought out, created so general a
sensation as the Kaleidoscope. Every person, who could buy or make one,
had a Kaleidoscope. Men, women, and children--rich and poor; in houses
or walking in the streets; in carriages, or on coaches--were to be seen
looking into the wonder-working tube, admiring the beautiful patterns
it produced, and the magical changes which the least movement of the
glass occasioned.
It was in the year 1814 that Sir David Brewster discovered the
principle on which the effects of the Kaleidoscope depend, whilst
he was engaged in experiments on the polarization of light by
successive reflections between plates of glass. The reflectors were
in some cases inclined to each other, and he remarked the circular
arrangement of the images of a candle round a centre. In afterwards
repeating the experiments of M. Biot on the action of fluids on
light, he placed the fluids in a trough formed by two plates of glass
cemented together at an angle. The eye being placed at one end, some
of the cement which pressed through between the plates appeared to be
arranged in a circular figure. The symmetry of this figure being very
remarkable, Sir David Brewster undertook to investigate the cause of
the phenomenon, and the result of his investigations was the invention
of the instrument to which he gave the name of Kaleidoscope, from the
Greek words καλος {kalos}, beautiful, ειδος {eidos}, a form, and σκοπεω
{skopeô}, to see.[4]
The Kaleidoscope in its simplest form consists of two equal strips of
plate glass, about 8 inches long and 2 inches wide, silvered on one
side, to act as reflectors. These glasses are placed one over the other
exactly, and then the edges on one side being separated, whilst the
two other edges are kept close together, they are fixed by means of
separating pieces of wood and string at the angle required. The glasses
are then fitted into a metal tube, which has an eye-hole at one end,
and at the other end of the tube there is fixed a small cell of ground
glass, to contain pieces of differently stained glass or other objects,
that are to be multiplied by reflections into beautiful symmetrical
figures. In the better kind of Kaleidoscopes, the cell containing the
objects may be turned round, by which means the pieces of glass shift
their positions, and the figures instantly change. The same effect is
produced, though in a less agreeable manner, in the common kind of
instruments, by turning the tube.
To form by the combined reflections from the two glasses a perfectly
symmetrical figure, the sector comprised between the inclined sides of
the glasses may consist of any even aliquot part of a circle. In the
accompanying diagram, the ends of the flat silvered glasses _a c_, _b
c_, are inclined at an angle of 60 degrees; therefore the circle is
completed by the junction of six sectors. In such a Kaleidoscope, the
circular figure will be formed by three reflections from each glass.
[Illustration]
[Illustration]
To make the formation of the circular figure by repeated reflections
more intelligible, we will consider it as composed of the smallest
possible number of equal divisions, as in the second diagram, in which
the circle is divided into quadrants. In such an arrangement of the
reflectors, the figure seen on looking through the central aperture
will consist of four parts. In the first place, the objects included in
the space _a b c_, between the inclined glasses, will be seen directly
by rays of light from the objects themselves; viz., the small cross
_d_, and the triangle _e_. The same field of view will be reflected
from both mirrors, by which reflection the cross on one side will
seem to be doubled, and the triangle on the other will have another
similar one added to it, to make a complete rhomb. The cross will also
be reflected by the mirror on the right side, and the triangle by the
one on the left. The images of the objects contained within the space
_a b c_, being thus presented by reflection on both sides, they become
the objects for further reflections from parts of the mirrors still
nearer the spectator. Thus the images _d_¹ on both sides are reflected
to form the single image _d_², and the images _e_¹ are in the same
manner reflected to form the second image _e_².
When the angle formed by the inclination of the mirrors divides the
circle into a greater number of sectors, the reflections of the images
are repeated, from points nearer and nearer to the eye, and the circle
is thus completed, however numerous the sectors may be; but at each
repetition of the reflection, the images will become more dim, since,
owing to the imperfection of reflecting surfaces, a portion of the
light is absorbed at each reflection.
In the first instruments that were constructed, the objects were
fixed in the field of view, therefore scarcely any change of pattern
was obtainable. It was not until some time afterwards that the idea
occurred to Sir David Brewster of producing endless changes of the
figures, by making the objects movable in a cell of glass at the end
of the instrument. He afterwards introduced other improvements in the
Kaleidoscope, for extending its range of objects, for varying the
angles of inclination, and for projecting the figures on a screen. In
the instrument, as ordinarily made, the objects to be seen properly
must be placed close to the end of the reflectors; but by the addition
to the instrument of a tube containing a lens, the rays from distant
objects are brought to a focus near the mirrors, and the image formed
there is repeated by the reflectors in the same manner as a solid
object.
The projection of the figures on a screen, by an apparatus similar to
a magic lantern, gives great additional pleasure to the effects of
the Kaleidoscope, as the figures are not only seen by several persons
at the same time, but they are presented in a magnified form. The
projection of the figures also increases the use of the instrument in
designing patterns, for which purpose it has been employed with great
advantage.
A patent for the Kaleidoscope was taken out in 1817, but the high
prices charged by the opticians who were authorized by the inventor
to sell the instrument, and the facility with which it could be
made, occasioned a general violation of the patent right, and it was
not long before the claim of Sir David Brewster, as the original
inventor, was disputed. In the indignant vindication of his claim, he
observes:--"There never was a popular invention which the labours of
envious individuals did not attempt to trace to some remote period;"
and the Kaleidoscope was not an exception. It was found that Kircher
had described the effects of repeated reflections as far back as
1630; and that Mr. Bradley had, in 1717, made a philosophical toy,
consisting of two small mirrors, that opened like a book, which, when
partially opened, repeated the reflections of objects placed near it
in the same manner as the Kaleidoscope. But this instrument was so
different in its construction, and in the effects it produced, from the
Kaleidoscope, that Sir David Brewster's claim to be the inventor may
be freely admitted. The fact that it took the world by surprise, and
created a sensation greater than any other invention had done before,
is sufficient to establish its title as an original invention.