ON THE KALEIDOSCOPE.

INTRODUCTION.

HISTORY OF THE KALEIDOSCOPE.

THE name KALEIDOSCOPE, which I have given to a new Optical Instrument, for creating and exhibiting beautiful forms, is derived from the Greek words xaλós, beautiful; εidos, a form; and oxoew, to see.

The first idea of this instrument presented itself to me in the year 1814, in the course of a series of experiments on the polarization of light by successive reflexions between plates of glass, which were published in the Philosophical Transactions for 1815, and which the Royal Society did me the honour to distinguish by the adju dication of the Copley Medal. In these experiments, the reflecting plates were necessarily inclined to each other during the operation of placing their surfaces in parallel planes; and I was therefore led to remark the circular arrangement of the images of a candle round a centre, and the multiplication of the sectors formed by the extremities

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of the plates of glass. In consequence, however, of the distance of the candles, &c., from the ends of the reflectors, their arrangement was so destitute of symmetry, that I was not induced to give any farther attention to the subject.

On the 7th of February 1815, when I discovered the development of the complementary colours, by the successive reflexions of polarized light between two plates of gold and silver, the effects of the Kaleidoscope, though rudely exhibited, were again forced upon my notice; the multiplied images were, however, coloured with the most splendid tints; and the whole effect, though inconceivably inferior to the creations of the Kaleidoscope, was still far superior to anything that I had previously witnessed.

In giving an account of these experiments to M. Biot on the 6th of March 1815, I remarked to him, "that when the angle of incidence (on the plates of silver) was about 85° or 86°, and the plates almost in contact, and inclined at a very small angle, the two series of reflected images appeared at once in the form of two curves; and that the succession of splendid colours formed a phenomenon which I had no doubt would be considered, by every person who saw it to advantage, as one of the most beautiful in optics." These experiments were afterwards repeated with more perfectly polished plates of different metals, and the effects were proportionally more brilliant ; but notwithstanding the beauty arising from the multiplication of the images, and the additional splendour which was communicated to the picture by the richness of the polarized tints, it was wholly destitute of symmetry, as I was then ignorant of those positions for the eye and the

objects, which are absolutely necessary to produce that magical union of parts, and that mathematical symmetry throughout the whole picture, which, independently of all colouring, give to the visions of the Kaleidoscope the peculiar charm which distinguishes them from all artificial creations.1

Although I had thus combined two plain mirrors, so as to produce highly pleasing effects, from the multiplication and circular arrangement of the images of objects placed at a distance from their extremities, yet I had scarcely made a step towards the invention of the Kaleidoscope. The effects, however, which I had observed, were sufficient to prepare me for taking advantage of any suggestion which experiment might afterwards throw in the way.

In repeating, at a subsequent period, the very beautiful experiments of M. Biot, on the action of homogeneous fluids upon polarized light, and in extending them to other fluids which he had not tried, I found it most convenient to place them in a triangular trough, formed by two plates of glass cemented together by two of their sides, so as to form an acute angle. The ends being closed up with pieces of plate glass cemented to the other plates, the trough was fixed horizontally, for the reception of the fluids. The eye being necessarily placed without the trough, and at one end, some of the cement, which had been pressed through between the plates at the object end of the trough, appeared to be

1 An account of the experiments above alluded to was given in the Analyse des Travaux de la Classe des Sciences Mathématiques et Physiques de l'Institut Royal de France, pendant l'année 1815, par M. le Chev. Delambre, p. 29, &c. The colours produced by repeated reflexions from plates of silver are those of Elliptical Polarization, and are explained at great length in my paper on that subject, published in the Philosophical Transactions for 1830.

arranged in a manner far more regular and symmetrical than I had before observed when the objects, in my early experiments, were situated at a distance from the reflectors. From the approximation to perfect symmetry which the figure now displayed, compared with the great deviation from symmetry which I had formerly observed, it was obvious that the progression from the one effect to the other must take place during the passage of the object from the one position to the other; and it became highly probable, that a position would be found where the symmetry was mathematically perfect. By investigating this subject optically, I discovered the leading principles of the Kaleidoscope, in so far as the inclination of the reflectors, the position of the object, and the position of the eye, were concerned. I found, that in order to produce perfectly beautiful and symmetrical forms, three conditions were necessary.

1. That the reflectors should be placed at an angle, which was an even or an odd aliquot part of a circle, when the object was regular, and similarly situated with respect to both the mirrors; or the even aliquot part of a circle when the object was irregular, and had any position what

ever.

2. That out of an infinite number of positions for the object, both within and without the reflectors, there was only one where perfect symmetry could be obtained, namely, when the object was placed in contact with the ends of the reflectors. This was precisely the position of the cement in the preceding experiment with the triangular trough.

3. That out of an infinite number of positions for the eye, there was only one where the symmetry was perfect,

namely, as near as possible to the angular point, so that the circular field could be distinctly seen; and that this point was the only one out of an infinite number at which the uniformity of the light of the circular field was a maximum, and from which the direct and the reflected images had the same form and the same magnitude, in consequence of being placed at the same distance from the eye. This, also, was the position in which the eye was necessarily placed when looking through the fluid with which the glass. trough was partially filled.

Upon these principles I constructed an instrument, in which I fixed permanently, across the ends of the reflectors, pieces of coloured glass, and other irregular objects; and I showed the instrument in this state to some members of the Royal Society of Edinburgh, who were much struck with the beauty of its effects. In this case, however, the forms were nearly permanent; and slight, though beautiful, variations were produced by varying the position of the instrument with respect to the source of light.

The great step, however, towards the completion of the instrument remained yet to be made; and it was not till some time afterwards that the idea occurred to me of giving motion to objects, such as pieces of coloured glass, &c., which were either fixed or placed loosely in a cell at the end of the instrument. When this idea was carried into execution, and the reflectors placed in a tube, and fitted up on the preceding principles, the Kaleidoscope, in its simple form, was completed.

In this form, however, the Kaleidoscope could not be considered as a general philosophical instrument of universal application.

The least deviation of the object from the