position of symmetry at the end of the reflectors, produced a deviation from beauty and symmetry in the figure, and this deviation increased with the distance of the object. The use of the instrument was therefore limited to objects in contact with the ends of the reflectors, or held close to them, and consequently to objects, or groups of objects, whose magnitudes were less than its triangular aperture. The next, and by far the most important step of the invention, was to remove this limitation, and to extend indefinitely the use and application of the instrument. This effect was obtained by employing a draw tube, containing a convex lens, or, what is better, an achromatic object-glass of such a focal length, that the images of objects, of all magnitudes and at all distances, might be distinctly formed at the end of the reflectors, and introduced into the pictures created by the instrument in the same manner as if they had been reduced in size, and placed in the true position in which alone perfect symmetry could be obtained. When the Kaleidoscope was brought to this degree of perfection, it was impossible not to perceive that it would prove of the highest service in all the ornamental arts, and would, at the same time, become a popular instrument for the purposes of rational amusement. With these views I thought it advisable to secure the exclusive property of it by a Patent ;1 but in consequence of one of the patent 1 As this Patent, in so far as the simple Kaleidoscope is concerned, was to a great extent infringed, it has been supposed that it was reduced in a Court of Law. The validity of the Patent was never questioned by any lawyer, or any philosopher acquainted with its theory and construction, as will appear from the opinion of four competent judges, given in the Appendir In a trial for the infringement of a Patent several years ago, a distinguished instruments having been exhibited to some of the London opticians, the remarkable properties of the Kaleidoscope became known before any number of them could be prepared for sale. The sensation excited by this premature exhibition of its effects is incapable of description, and can be conceived only by those who witnessed it. "It very quickly became popular," says Dr. Roget, in his excellent article on the KALEIDOSCOPE in the Encyclopædia Britannica," and the sensation it excited in London throughout all ranks of people was astonishing. It afforded delight to the poor as well as the rich; to the old as well as the young. Large cargoes of them were sent abroad, particularly to the East Indies. They very soon became known throughout Europe, and have been met with by travellers even in the most obscure and retired villages in Switzerland." According to the computation of those who were best able to form an opinion on the subject, no fewer than two hundred thousand instruments were sold in London and Paris during three months. Out of this immense number there were perhaps not one thousand constructed upon scientific principles, and capable of giving anything like a correct idea of the power of the Kaleidoscope; and of the millions who have witnessed its effects, there is perhaps not a hundred individuals who have any idea of the principles upon which it is constructed, who are capable of distinguishing the spurious from the real instrument, or who have sufficient knowledge of its principles to be able judge (we believe it was Judge Alderson) stated it as a fact, that the Patent for the Kaleidoscope had been set aside in a Court of Law. The party whose case was prejudiced by this erroneous assertion, applied to me for an affidavit, by which he was enabled to contradict it in Court, and remove any unfavourable impression it might have made upon the jury. to apply it to the numerous branches of the useful and ornamental arts. Under these circumstances I have thought it necessary to draw up the following short treatise, for the purpose of explaining, in as popular a manner as I could, the principles and construction of the Kaleidoscope; of describing the different forms in which it is fitted up; of pointing out the various methods of using it as an instrument of recreation; and of instructing the artist how to employ it in the numerous branches of the useful and ornamental arts to which it is applicable. CHAPTER I. PRELIMINARY PRINCIPLES RESPECTING THE EFFECTS OF THE principal parts of the Kaleidoscope are two reflecting planes, made of glass, or metal, or any other reflecting substance ground perfectly flat and highly polished. reflectors, which are generally made of plate-glass, either These rough ground on their outer side, or covered with black varnish, may be of any size, but in general they should be from four or five to ten or twelve inches long; their greatest breadth being about an inch when the length is six inches, and increasing in proportion as the length increases. When these two plates are put together at an angle of 60°, or the sixth part of a circle, as shown in Fig. 1, and the eye placed at the narrow end E, it will observe the opening A O B multiplied six times, and arranged round the centre o, as shown in Fig. 2. In order to understand how this effect is produced, let us take a small sector of white paper of the shape A O B, Fig. 2, and having laid it on a black ground, let the extremity A o of one of the reflectors be placed upon the edge A o of the sector. It is then obvious that an image A ob of this white sector of paper will be formed behind the mirror a o, and will have the same magnitude and the same situation behind the mirror as the sector A O B had before it. In like manner, if we place the edge BO of the other reflector upon the other side B o of the paper sector, a similar image Boa will be formed behind it. The origin of three of the sectors seen round o is therefore explained the first, A O B, is the white paper sector seen by direct vision; the second, A o b, is an image of the first formed by one reflexion from the mirror a o; and the third is another image of the first formed by one reflexion from |