APPENDIX.

Although I have no doubt that the observations contained in the preceding Chapters are sufficient to satisfy every candid and intelligent person respecting the true nature of all the combinations of plane mirrors that preceded the invention of the Kaleidoscope, yet as there are many who are incapable, from want of optical knowledge, to understand the comparison which has been made between them, I shall here present the opinions of four of the most eminent mathematicians and natural philosophers.

The first of these is contained in a note from the late Professor Wood, Master of St. John’s College, Cambridge, written in reply to a letter, in which I requested him to say, if he had any idea of the effects of the Kaleidoscope when he wrote the thirteenth and fourteenth Propositions of his works on Optics.

“St. John’s, May 19, 1818.

“Sir,—The propositions I have given relating to the number of images formed by plane reflectors, inclined to each other, contain merely the mathematical calculation of their number and arrangement. The effects produced by the Kaleidoscope were never in my contemplation. My attention has for some years been turned to other subjects, and I regret that I have not time to read your Optical Treatise, which I am sure would give me great pleasure.—I am, Sir, your obedient humble servant,

“J. Wood.”

The following is the opinion of the late celebrated Mr. James Watt:—

“It has been said here,” says Mr. Watt, “that you took the idea of the Kaleidoscope from an old book on gardening. My friend, the Rev. Mr. Corrie, has procured me a sight of the book. It is Bradley’s Improvements of Planting and Gardening. London, 1731, Part II. Chap. I. It consists of two pieces of looking-glass, of equal bigness, of the figure of a long square, five inches long, and four inches high, hinged together upon one of the narrow sides, so as to open and shut like the leaves of a book, which, being set upon their edges upon a drawing, will show it multiplied by repeated reflexions. This instrument I have seen in my father’s possession seventy years ago, and frequently since, but what has become of it I know not. In my opinion, the application of the principle is very different from that of your Kaleidoscope.”

The following is the opinion of the late Mr. Playfair, Professor of Natural Philosophy in the University of Edinburgh:—

“Edinburgh, May 11, 1818.

“I have examined the Kaleidoscope invented by Dr. Brewster, and compared it with the description of an instrument which it has been said to resemble, constructed by Bradley in 1717. I have also compared its effect with an experiment to which it may be thought to have some analogy, described by Mr. Wood in his Optics, Prop. xiii. and xiv.

“From both these contrivances, and from every optical instrument with which I am acquainted, the Kaleidoscope appears to differ essentially, both in its effect and in the principles of its construction.

“As to the effect, the thing produced by the Kaleidoscope is a series of figures presented with the most perfect symmetry, so as always to compose a whole, in which nothing is wanting and nothing redundant. It matters not what the object be to which the instrument is directed; if it only be in its proper place, the effect just described is sure to take place, and with an endless variety. In this respect the Kaleidoscope appears to be quite singular among optical instruments. Neither the instrument of Bradley, nor the experiment or theorem in Wood’s book, have any resemblance to this; they go no further than the multiplication of the figure.

“Next, as to the principle of construction, Dr. Brewster’s instrument requires a particular position of the eye of the observer, and of the object looked at, in order to produce its effect. If either of these is wanting, the symmetry vanishes, and the figures are irregular and disunited. In the other two cases, no particular position, either for the eye or the object, is required.

“For these reasons, Dr. Brewster’s invention seems to me quite unlike the other two. Indeed, as far as I know, it is quite singular among optical instruments; and it will be matter of sincere regret, if any imaginary or vague analogy, between it and other optical instruments, should be the means of depriving the Doctor of any part of the reward to which his skill, ingenuity, and perseverance, entitle him so well.

“John Playfair, Professor of Natural Philosophy in the University of Edinburgh.”

“P.S.—Granting that there were a resemblance between the Kaleidoscope and Bradley’s instrument, in any of the particulars mentioned above, the introduction of coloured and movable objects, at the end of the reflectors, is quite peculiar to Dr. Brewster’s instrument. Besides this, a circumstance highly deserving of attention, is the use of two lenses and a draw-tube; so that the action of the Kaleidoscope is extended to objects of all sizes, and at all distances from the observer, and united, by that means, to the advantages of the telescope.

“J. P.”

Professor Pictet’s opinion is stated in the following letter:—

“Sir,—Among your friends, I have not been one of the least painfully affected by the shameful invasion of your rights as an inventor, which I have been a witness of lately in London. Not only none of the allegations of the invaders of your patent, grounded on a pretended similarity between your Kaleidoscope and Bradley’s instrument, or such as Wood’s or Harris’s theories might have suggested, appear to me to have any real foundation; but I can affirm, that, neither in any of the French, German, or Italian authors, who, to my knowledge, have treated of optics, nor in Professor Charles’s justly-celebrated and most complete collection of optical instruments at Paris, have I read or seen anything resembling your ingenious apparatus, which, from its numberless applications, and the pleasure it affords, and will continue to afford to millions of beholders of its matchless effects, may be ranked among the most happy inventions that science ever presented to the lovers of rational enjoyment.

“M. A. Pictet, Professor of Natural Philosophy in the Academy of Geneva.”

Those who wish to examine farther the ancient combinations of plane mirrors, and other subjects connected with the Kaleidoscope, are referred to the following works:—

Baptista Porta’s Magia Naturalis. Kircher’s Ars Magna Lucis et Umbræ. Schottus’s Magia Universalis Naturæ et Artis. Bradley’s Treatise on Planting and Gardening. Harris’s Treatise on Optics. Wood’s Optics. Dr. Roget on the Kaleidoscope, in the Annals of Philosophy, vol. xi. p. 375. Encyclopædia Britannica, Art. Kaleidoscope, by Dr. Roget; and the Compte Rendu des Travaux de L’Académie de Dijon, pour 1818, pp. 108-117.

Works by SIR DAVID BREWSTER.

MORE WORLDS THAN ONE: the Creed of the Philosopher, the Hope of the Christian. Cr. 8vo., 4s. 6d.

THE MARTYRS OF SCIENCE: Galileo, Tycho Brahe, and Kepler. Cr. 8vo., 4s. 6d.

THE KALEIDOSCOPE Practically Described. Cr. 8vo., with Illustrations, 4s. 6d.

THE STEREOSCOPE Practically Described. Cr. 8vo., with Illustrations, 4s. 6d.

London: JOHN CAMDEN HOTTEN, 74, PICCADILLY.

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