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.