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.

Upon these principles Dr B. constructed an instrument, in which he fixed permanently across the ends of reflectors, pieces of coloured glass, and other irregular objects, and he shewed 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 a slight variation was produced by varying the position of the instrument, with respect to the 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 Dr B. 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, the kaleidoscope, in its simple form, was completed.

In this state, however, the kaleidoscope could not be considered as a general philosophical instrument of universal application; for it was incapable of producing beautiful forms unless the object was nearly in perfect contact with the end of the reflectors.

The next, and by far the most important step of the invention, was therefore to remove this limitation by employing a draw tube and lens, by means of which beautiful forms could be created from objects of all sizes, and at all distances from the observer. In this way the power of the kaleidoscope was indefinitely extended, and every object in nature could be introduced into the picture, in the same manner as if these objects had been reduced in size, and actually placed at the end of the reflectors.

When the instrument was brought to this state of perfection, Dr Brewster was urged by his friends to secure the exclusive property of it by a patent, and he accordingly took out a patent for "a New Optical Instrument for creating and exhibiting beau

tiful forms." In the specification of his patent he describes the kaleidoscope in two different forms. The first consists of two reflecting planes, put together according to the principles already described, and placed in a tube, with an eye-hole in the particular position which gives symmetry and a maximum uniformity of light, and with objects such as coloured glass, placed in the position of symmetry, and put in motion either by a rotatory movement, or by their own gravity, or by both combined. The second form of the instrument, described in the specification, is, when the tube containing the reflectors is placed in a second tube, at the end of which is a convex lens which introduces into the picture objects of all magnitudes, and at every distance, as has been already described.

After the patent was signed, and the instruments in a state of forwardness, the gentleman who was employed to manufacture them under the patent, carried a kaleidoscope to shew to the principal London Optician, for the purpose of taking orders from them. These gentlemen naturally made one for their own use, and for the amusement of their friends; and the character of the instrument being thus made public, the tinmen and glaziers began to manufacture the detached parts of it, in order to evade the patent; while others manufactured and sold the instrument complete, without being aware that the exclusive property of it had been secured by a patent.

In this way the invasion of the patent right became general among that class of individuals against whom the law is seldom enforced but in its terrors. Some workmen of a higher class were encouraged to piracy by this universal opposition to the patent; but none of the respectable London opticians would yield to the clamours of their customers, to encroach upon the rights of an inventor, to whom they were at least indebted for a new and a lucrative article of trade.

In order to justify these piratical proceedings, it became necessary to search for some combinations of plain mirrors, which might be supposed to have a resemblance to Dr Brewster's instrument; and it would have been strange indeed, if some theorem or experiment had not been discovered, which could have been used to impose upon the great crowd who are

entirely ignorant of the principles and construction of optical instruments. There never was a popular invention, which the labours of envious individuals did not attempt to trace to some remote period; and in the present case, so many persons had hazarded their fortunes and their characters, that it became necessary to lay hold of something which could be construed into an anticipation of the kaleidoscope.

The first supposed anticipation of the kaleidoscope was found in Prop. XIII. and XIV. of Professor Wood's Optics, where that learned author gives a mathematical investigation of the number and arrangement of the images formed by two reflectors, either inclined or parallel to each other. These theorems assign no position either to the eye or to the object, and do not even include the principle of inversion, which is absolutely necessary to the production of symmetrical forms. The theorems in deed are true, whatever be the position of the object or of the eye. In order to put this matter to rest, Dr Brewster wrote a letter to Professor Wood, requesting him to say if he had any idea of the effects of the kaleidoscope when he wrote these propositions. To this letter Dr B. received the following handsome and satisfactory answer:

"St Johns, May 19th, 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 next supposed anticipation of the kaleidoscope was an instrument proposed by Mr Bradley in 1717. This instrument consists of two large pieces of silvered looking-glass, five inches wide and four inches high, jointed together with hinges, and opening like a book. These plates being set upon a geometrical drawing, and the eye

being placed in front of the mirrors, the lines of the drawing were seen multiplied by repeated reflections. This instrument was described long before by Kircher, and did not receive a single improvement from the hands of Bradley. It has been often made by the opticians, and was principally used for multiplying the human face, when placed between the mirrors; but no person ever thought of applying it to any purpose of utility, or of using it as an instrument of rational amusement, by the creation of beautiful forms. From the very construction of the instrument, indeed, it is quite incapable of producing any of the singular effects exhibited by the kaleidoscope. It gives, indeed, a series of reflected images arranged round a centre; but so does a pair of lookingglasses placed angularly in an apartment, and so do the pieces of mirror glass with which jewellers multiply the wares exhibited at their windows. It might therefore be as gravely maintained that any of these combinations of mirrors was a kaleidoscope, as that Bradley's pair of plates was an anticipation of that instrument. As the similarity between the two has been maintained by ignorant and interested individuals, we shall be at some pains to explain to the reader the differences between these two instruments; and we shall do this, first, upon the supposition that the two instruments are applied to geometric lines upon paper.

1. In Bradley's instrument, the length is less than the breadth of the plates.

2. Bradley's instrument cannot be used with a tube.

3. In Bradley's instrument, from the erroneous position of the eye, there is a great inequality of light in the sectors, and the last sectors are scarcely visible.

4. In Bradley's instrument, the figure consists of

1. In the kaleidoscope, the length of the plates must be four, or five, or six times their breadth.

2. The kaleidoscope cannot be used without a tube.

3. In the kaleidoscope, the eye is placed so that the uniformity of light is a maximum, and the last sectors are distinctly visible.

4. In the kaleidoscope, all the sectors are equal,

elliptical, and consequently unequal

sectors.

5. In Bradley's instrument, the unequal sectors do not unite, but are all separated from one another by a space equal to the thickness of the mirror glass. 6. In Bradley's instrument, the images reflected from the first surface interfere with those reflected from the second, and produce confusion and overlapping of images entirely inconsistent with symmetry. 7. In Bradley's instrument, the defects in the junction of the plates are all rendered visible by the erroneous position of

the eye.

a

The reader will observe, that in this comparison the two instruments are supposed to be applied to geometric lines upon paper, and that this was the only purpose to which Bradley ever thought of applying his mirrors; yet the kaleidoscope is in every respect a superior instrument, even for that inferior purpose, and gives true symmetrical forms, which the other instrument is incapable of doing.

In the comparison which has now been made, we have degraded the kaleidoscope, by contrasting its effects with those which Bradley's instrument is capable of producing for these effects are not worth the looking at. When we attempt to employ Bradley's instrument to produce the effects which have been so much admired in the kaleidoscope, namely, to produce beautiful forms from transparent or opaque coloured objects contained in a cell, and at the end of the reflectors, it fails so entirely, that no person has succeeded in the attempt. It is indeed quite impossible to produce by it the

beautiful and symmetrical forms which the kaleidoscope displays. Had this been possible, Dr Brewster's patent might have been invaded with impunity by every person who chose to manufacture Bradley's instrument; but this was never tried*, and for the best of all reasons, because nobody would have purchased it.

We trust that no person, who wishes to judge of this subject with candour, will form an opinion without having actually seen and used the instrument proposed by Bradley. Let any person take Bradley's plates, and, having set them at an angle of 30° or 224°, place them upon a cell containing fragments of coloured glass, he will infallibly find that he cannot produce a picture of any symmetry or beauty. The disunion of the sectors, the darkness of the last reflections, and the enormous deviation from symmetry, towards the centre of the figure, will convince him, if he required conviction, that the instrument is entirely useless as a kaleidoscope. To those, however, who are not capable, either for want of knowledge, or want of time, to make such a comparison, we may present the opinion of three of the most eminent natural philosophers of the present day, viz. the celebrated Mr Watt, Professor Playfair, and Professor Pictet.

"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 2d. chap.

1st.

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

* In illustration of this argument, we may state the following fact. Mr Carpenter of Birmingham, being anxious to evade Dr Brewster's patent, at a time when the manufacture of the patent kaleidoscope was in the hands of another person, at

tempted to construct instruments in imitation of Bradley's. After exercising his ingenuity for some time, he abandoned the attempt as impracticable, and set off for Scotland for the purpose of offering his services in manufacturing the patent instrument.

edges upon a drawing, will shew it multiplied by repeated reflections. This instrument I have seen in my father's possession 70 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 kaleidoscope." your The following is Professor Playfair's opinion:

Edinburgh, 11th May 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. 13 and 14.

"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 its effect. If elther 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 moveable 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:

66

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' 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' justly celebrated and most complete collection of optical instruments at Paris, have I read or seen

any thing resembling your ingeniberless applications, and the pleasure ous apparatus, which, from its numit affords, and will continue to afford, to millions of beholders of its matchless effects, may be ranked among the most happy inventions science ever presented to the lovers of rational enjoyment.

M. A. PICTET, Professor of Nat. Phil. in the Academy of Geneva.

To Dr Brewster."

The propositions in Harris' Optics relate, like Professor Wood's, merely

to the multiplication and circular arrangement of the apertures or sectors formed by the inclined mirrors, and to the progress of a ray of light reflected between two inclined or parallel mirrors; and no allusion whatever is made, in the propositions themselves, to any instrument. In the proposition respecting the multiplication of the sectors, the eye of the observer is never once mentioned, and the proposition is true if the eye has an infinite number of positions; whereas, in the kaleidoscope, the eye can only have one position. In the other proposition, (Prop. XVII.) respecting the progress of the rays, the eye and the object are actually stated to be placed between the reflectors; and even if the eye had been placed without the reflectors, as in the kaleidoscope, the position assigned it, at a great distance from the angular point, is a demonstration that Harris was entirely ignor ant of the positions of symmetry either for the object or the eye, and could not have combined two reflectors so as to form a kaleidoscope for producing beautiful or symmetrical forms. The only practical part of Harris's propositions is the 5th and 6th scholia to Prop. XVII. In the 5th scholium he proposes a sort of catoptric box or cistula, known long before his time, composed of four mirrors, arranged in a most unscientific manner, and containing opaque objects between the speculums. "Whatever they are," says he, when speaking of the objects, "the upright figures between the speculums should be slender, and not too many in number, otherwise they will too much obstruct the reflected rays from coming to the eye.' This shews, in a most decisive manner, that Harris knew nothing of the kaleidoscope, and that he has not even improved the common catoptric cistula, which had been known long before. The principle of inversion, and the positions of symmetry, were entirely unknown to him. In the 6th scholum, he speaks of rooms lined with looking-glasses, and of luminous amphitheatres, which, as the Editor of the Literary Journal observes, have been described and figured by all the old writers on optics.

"

The reader is requested to examine carefully the propositions in Harris' Optics, which he will find reprinted in the Literary

The persons who have pretended to compare Dr Brewster's kaleidoscope with the combinations of plain mirrors described by preceding authors, have not only been utterly unacquainted with the principles of optics, but have not been at the trouble either of understanding the principles on which the patent kaleidoscope is constructed, or of examining the construction of the instrument itself. Because it contains two plain mirrors, they infer that it must be the same as every other instrument that contains two plain mirrors; and hence the same persons would, by a similar process of reasoning, have concluded that a telescope is a microscope, or that a pair of spectacles with a double lens is the same as a telescope or a microscope, because all these instruments contain two lenses. An astronomical telescope differs from a compound microscope only in having the lenses placed at different distances. The progress of the rays is exactly the same in both these instruments, and the effect in both is produced by the enlargement of the angle subtended by the object. Yet surely there is no person so senseless as to deny that he who first combined two lenses in such a manner as to discover the mountains of the moon, the satellites of Jupiter and Saturn, and all the wonders of the system of the universe, was the author of an original invention. He who produces effects which were never produced before, even by means which have been long known, is unquestionably an original inventor; and upon this principle alone can the telescope be considered as an invention different from the microscope. In the case of the kaleidoscope, the originality of the invention is far more striking. Every person admits that effects are produced by Dr Brewster's intrument, of which no conception could have been previously formed. All those who saw it, acknowledged that they had never seen any thing resembling it before; and those very persons who had been possessors of Bradley's instrument, who had read Harris's Optics, and made his shew boxes, and who had used other combinations of plain mirrors, never

Journal, No 10. He will then be convinced, that Harris placed both the eye and the object between the mirrors, an arrangement which was known 100 years before his time.