of different depths of shadow, advancing into, or emerging from the centre of symmetry, or passing across the radial lines of the figure at different obliquities, would assist in marking more emphatically the gay or the gloomy sounds with which they are accompanied.

A slight idea of the effects which might be expected from an ingenious piece of mechanism for creating and combining the various optical phenomena, and exhibiting them in connexion with musical sounds, may be obtained by a single observer, who looks into a fine Kaleidoscope, firmly fixed upon a stand, and produces with his two hands all the variations in form and colour which he can effect by such inadequate means, and which he considers appropriate to the musical piece that accompanies them.

CHAPTER XXIII.

HISTORY OF THE COMBINATIONS OF PLANE MIRRORS WHICH HAVE BEEN SUPPOSED TO RESEMBLE THE KALEIDOSCOPE.

IT has always been the fate of new inventions to have their origin referred to some remote period; and those who labour to enlarge the boundaries of science, or to multiply the means of improvement, are destined to learn, at a very early period of their career, that the desire of doing justice to the living is a much less powerful principle than that of being generous to the dead. This mode of distributing fame, injurious as it is to the progress of science, by taking away one of the strongest excitements of early genius, has yet the advantage of erring on the side of generosity; and there are few persons who would reclaim against a decision invested with such a character, were it pronounced by the grave historian of science, who had understood and studied the subject to which it referred.

The apparent simplicity, both of the theory and the construction of the Kaleidoscope, has deceived very well-meaning persons into the belief that they understood its mode of operation; and it was only those that possessed more than a moderate share of optical knowledge, who saw that it was not only more difficult to understand, but also more difficult to execute, than most of the philosophical instruments now

in use. The persons who considered the Kaleidoscope as an instrument consisting of two reflectors, which multiplied objects, wherever these objects were placed, and whatever was the position of the eye, provided that it received only the reflected rays, were at no loss to find numerous candidates for the invention. All those, indeed, who had observed the multiplication and circular arrangement of a fire blazing between two polished plates of brass or steel; who had dressed themselves by the aid of a pair of looking-glasses, or who had observed the effects of two mirrors placed upon the rectangular sides of a drawing-room, were entitled, upon such a definition, to be constituted inventors of the Kaleidoscope. The same claim might be urged for every jeweller who had erected in his window two perpendicular mirrors, and placed his wares before them, in order to be multiplied and exhibited to advantage; and for every Dutch toymaker, and dealer in optical wonders, who had manufactured show-boxes, for the purpose of heaping together, in some sort of order, a crowd of images of the same object, of different intensities, seen under different angles, and presenting different sides to the eye. This mode of group

ing images, dissimilar in their degree of light, dissimilar in their magnitude, and dissimilar in their very outlines, produced such a poor effect, that the reflecting show-boxes have for a long series of years disappeared from among the number of philosophical toys.

From these causes, the candidates for the merit of inventing the Kaleidoscope have been so numerous, that they have started up in every part of the world; and many individuals, who are scarcely acquainted with the equality of the angles of incidence and reflexion, have not scrupled

to favour the world with an account of the improvements which they fancy they have made upon the instrument. 1

The earliest writer who appears to have described the use of two plane mirrors, was Baptista Porta, who has given an account of several experiments which he performed with them, in the second chapter of the seventh book of his Magia Naturalis.

As the combination of plane mirrors which he there describes has been represented as the same as the Kaleidoscope, we shall give the passage at full length :—

Speculum è planis multividum construere.

"Speculum construitur, quod polyphaton id est multorum visibilium dicitur, illud enim aperiendo et claudendo solius digiti viginti et plura demonstrat simulacra. Sic igitur id parabis. Ærea duo specula vel crystallina rectangula super basim eandem erigantur, sintque in hemiolia proportione, vel alia, et secundum longitudinis latus unum simul colligentur, ut libri instar apte claudi et aperiri possint, et anguli diversentur, qualia Venetiis factitari solent faciem enim unam objiciens, in utroque plura cernes ora, et hoc quanto arctius clauseris, minorique fuerint angulo : aperiendo autem minuentur ; et obtusiori cernes angulo, pauciora numero conspicientur. Sic digitum ostendens, non nisi digitos cernes, dextra insuper dextra, et sinistra sinistra convisun

1 It would be an easy matter to amuse the reader with an account of these improvements. One of the most notable of them consists in covering the back of the reflectors with white paint, for the purpose of increasing the light of the circular field. This scheme is identically the same as if the author had proposed to improve the magnificent telescopes of Herschel, when rendered dark with a high magnifying power, by white-washing the interior of the tube.

tur; quod speculis contrarium est: mutuaque id evenit reflexione, et pulsatione, unde imaginum vicissitudo."Edit. Amstelod, 1664.

The following is an exact and literal translation of this passage :

How to construct a multiplying speculum out of plane ones.

A speculum is constructed, called polyphaton, that is, which shows many objects, for by opening and shutting it, it exhibits twenty and more images of the finger alone. You will therefore prepare it in the following manner :— Let two rectangular specula of brass or crystal be erected upon the same base, and let their length be one and a half times their width, or in any other proportion; and let two of their sides be placed together, so that they may be opened and shut like a book, and the angles varied, as they are generally made at Venice. For by presenting your face, you will see in both more faces the more they are shut, and the less that the angle is; but they will be diminished by opening it, and you will see fewer as you observe with a more obtuse angle. If you exhibit your finger, you will see only fingers, the right fingers being seen on the right side, and the left on the left side, which is contrary to what happens in looking-glasses, and this arises from the mutual reflexion and repulsion which produce a change of the images.

1

1 We request that the reader will take the trouble of comparing with the original the following translation of Baptista Porta's description, which was published in London, and copied into all the foreign newspapers, etc. We hope the translator of it had no improper motive in altering the obvious meaning of the original; yet