“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.