The writer has often seen a singular transformation effected by an ingenious device, called the optical paradox: thus an eagle may be changed into a lion, and a dog into a cat.
For this purpose, a wooden three-sided box must be prepared, and through the open part may slide the various drawings to be used, as B. Connected with this, there must be a pillar, C, and a horizontal bar holding a tube, D, having in it a glass placed exactly over the centre. The change is partly dependent on the glass, the sides of which are flat and diverge from its hexagonal base upwards, to a point in the axis of the glass, like a pyramid, E, forming an isosceles triangle. All that is now necessary to the completion of the change, is in the border of the drawing, in which the various parts required for the new figure are cleverly introduced; so that when the distance of the glass from the eye is rightly adjusted, each angular side will take up its portion from the border, and present to the eye the various parts in an entire figure. The shape of the glass prevents the appearance of any particular figure in the centre, as the eagle, for instance; while the lion, arranged in portions and drawn on the circle of refraction at six different parts of the border, yet artfully disguised by blending with it, the transformation will be completely produced.
A paper has lately been read to the Academy of Sciences at Paris, by M. Stanislaus Julien, on the metallic mirrors made in China, and to which the name of “magic mirrors” has been given. Hitherto all attempts by Europeans to obtain information as to the process, in the localities where they are manufactured, have proved failures, some of the persons applied to being unwilling to reveal the secret, and others being ignorant of the process. These mirrors are called magical, because, if they receive the rays of the sun on their polished surface, the characters, or flowers in relief, which exist on the other side, are faithfully reproduced. The following information has been obtained by M. Julien, from the writings of an author named Ou-tseu-hing, who lived between 1260 and 1341:—“The cause of this phenomenon is the distinct use of fine copper and rough copper. If, on the under side, there be produced, by casting in a mould, the figure of a dragon in a circle, there is then engraved deeply on the disc a dragon exactly similar. Then, the parts which have been cut are filled with rather rough copper; and this is, by the action of fire, incorporated with the other metal, which is of a finer nature. The face of the mirror is next prepared, and a slight coating of tin is spread over it. If the polished disc of a mirror so prepared be turned towards the sun, and the image be reflected on a wall, it presents distinctly the clear portion and the dark portion, the one of the fine, and the other of the rough copper.” Ou-tseu-hing states, that he had ascertained this by a careful inspection of the fragments of a broken mirror.
It is easy for an ignorant and superstitious mind to confound a very harmless and simple instrument with one of magical power. We have an example of this in Dodwell’s description of his residence at Athens. On his first admission within the venerable walls of the Acropolis, it was necessary to offer a small present to the disdar, or Turkish governor, and an additional sum to make drawings and observations without being molested by the servants of the garrison. The disdar proved to be a man of bad faith and insatiable rapacity, and, after experiencing numerous vexations from the mercenary Turk, Dodwell was at length released from his importunities by a singular circumstance. As he was one day engaged in drawing the Parthenon, with the aid of his camera obscura, the disdar, whose surprise was excited by the novelty of the sight, asked, with a sort of fretful inquietude, what new conjuration he was performing with that extraordinary machine. Dodwell endeavoured to explain it, by putting in a clean sheet of paper, and making him look at the instrument; but he no sooner saw the Temple of Minerva reflected on the paper in all its lines and colours, than he imagined the effect was produced by some magical process; his astonishment appeared mingled with alarm, and, stroking his long black beard, he repeated several times the words Allah, Masch-Allah—a term of admiration with the Turks, signifying that which is made by God.
Again he looked into the camera obscura, with a kind of cautious diffidence, and, at that moment, some of his soldiers happening to pass before the reflecting-glass, were beheld by the astonished disdar walking upon the paper. He now became outrageous; he assailed Dodwell with various opprobrious epithets, one of which was Bonaparte—the appellation being at the time synonymous to that of magician, or of any one supposed to be endowed with supernatural talents—and declared that, if Dodwell chose, he might take away all the stones in the temple, but that he would not permit his soldiers to be conjured into a box. “When I found,” says Dodwell, “that it was no use to reason with his ignorance, I changed my tone, and told him that, if he did not leave me unmolested, I would put him into my box; and that he should find it a very difficult matter to get out again. His alarm was now visible; he immediately retired, and ever after stared at me with a mixture of apprehension and amazement. When he saw me come to the Acropolis, he carefully avoided my approach; and never afterwards gave me any further molestation.”
The portable camera obscura, represented by the diagram, has often yielded much pleasure in the domestic circle, while the larger ones, which are publicly exhibited, are highly interesting. No person, perhaps, has witnessed the neatness of outline, the precision of form, the truth of colouring, and the sweet gradations of tint, thus apparent, without regretting that an imagery so exquisite and faithful to nature could not be made to fix itself permanently on the tablet of the machine. Yet, in the estimation of all, such a wish seemed destined to take its place among other dreams of beautiful things; the splendid but impracticable conceptions in which men of science and ardent temperament have sometimes indulged. Such a dream, however, has been realized of late.
