O the ignorant mind every occurrence or appearance out of the ordinary course of observation seems a wonder-something mysterious and incomprehensible. The whole scheme of creation and Providence is no doubt wonderful; but there are no phenomena obvious to the senses, which cannot be less or more explained in reference to certain acknowledged principles in science. Trained in scientific knowledge, therefore, none of the phenomena of nature excites in us any surprise. To the man of science there are no wonders, in the ordinary acceptation of that term. The seeming marvel which would fill an illiterate multitude with awe, and perhaps consternation, is to the cultivated and instructed mind no marvel at all. From this liability to deception, the illiterate of all ages have suffered under the thraldom of superstition, and been exposed to the fraudulent tricks of pretended magicians and other impostors. In ancient Egypt, Greece, and Rome, the populace, kept purposely in ignorance, were the constant dupes of priests, pretended sorcerers, and oracles, whose marvellous performances are now well known to have been within the reach of practical science. In the modern world, from the greater diffusion of knowledge, it has become more difficult to terrify or strike awe with performances of this nature; yet there are countries--some parts of Italy, for example-where, from the prevailing ignorance of the people, deceptions as gross as those of ancient Egypt or Greece are still unblushingly practised. Desirable as it is to possess a knowledge of science for the purpose of arming us against such deceptions, it is not less necessary to have this knowledge, in

order to shield us against our own naturally wonder-loving minds; for it may with truth be said, that if mankind had not in their own nature possessed a craving for the marvellous, they could not have been so easily made the dupes of imposture. Referring to the appropriate treatises for such instruction as may be requisite, we propose in the present sheet to stimulate inquiry, by pointing out some of the more amusing phenomena revealed by optics, acoustics, chemistry, and some other branches of science-the marvels wrought by the potent and magical wand of nature.

OPTICS PHENOMENA OF SIGHT.

The eye may be described as a beautiful optical instrument, consisting of a combination of lenses with a mirror. The lenses are certain transparent humours within the rounded part in front; and through these, as through the glass of a window, the rays of light, bringing the representation of objects, penetrate to the mirror behind. This mirror, called the retina, is not larger than the side of a split pea, and presents a hollowed surface to the rays. The representation of objects being formed in this little mirror, a nerve, called the optic nerve, in connexion with it, carries the impression of the picture to the brain. The eye is thus only the instrument of vision; it is the brain, or organ of thought, which truly sees.

OCULAR ILLUSIONS.

No artificial mirror is so susceptible of impressions as the retina. Such is its delicacy, that it has the power of retaining for a certain period of time the impression of any image after the object which produces the image is withdrawn. This leads to numerous ocular illusions. If we take a burning stick, and whirl it rapidly round before us, we think we see circles of fire; the eye not being able to perceive that it is only a burning point in rapid motion. At every part of its course the burning point leaves an impression on the retina for the eighth of a second; and hence the illusion. In the same manner we are deceived with streaks of lightning. The streaks, however seemingly continuous and zig-zag in their course, are only electric sparks in exceedingly rapid motion.

Some very interesting philosophical toys have been made from a knowledge of the above optical phenomenon. One of the most common consists of several pieces of card arranged edge to edge (as in a fan) round an axle. On each card is painted part of a human figure; as the head on one, the body on another, arms on a third, legs on a fourth, and so on-the whole sufficient to make up an entire figure. The illusion is produced by moving the cards rapidly round by a simple kind of mechanism; when the eye, losing all trace of the separate parts, perceives only a con

tinuous and complete figure. When several figures-as a Harlequin and Columbine-are painted in parts on the cards, the deception and drollery of the movements are more effective.

In some of these toys the cards are arranged along the axle, like cogs on a mill-wheel, and by their rapid turning we procure all the effects of a transparency. So varied are the illusions that may be practised by this species of toy, that, in the hands of the cunning deceivers of the ancient world, it might have been made an exceedingly serviceable instrument of superstition.

The susceptibility of the eye is very observable in the case of looking intently for even a moment at a bright object; on turning from the object, it leaves a spectral representation, like a round spot of green, orange, or some other bright colour in the eye. When the sun strikes the eye, this luminous image of varying colour produces an unpleasant sensation, which remains for a few minutes afterwards.

LENSES.

An object is said to be represented to our sight by means of rays coming from it to the eye. The rays come in a straight line towards our vision, unless bent out of their course by a medium whose density differs from that of the atmosphere. This bending is called refraction, which means breaking.

Refraction may take place by the rays going through two or more media of different densities, as air and water, air and pieces of glass of a peculiar form, &c. The glasses employed to refract rays are called lenses. Three kinds of lenses may be noticedthose for multiplying, for magnifying, and for diminishing. All are made of very pure glass:

When we look through a piece of glass pure and flat on both sides, we see nothing remarkable. The rays from any object are no way bent out of their course to the eye. If, however, we take a piece of glass flat on one side, and cut into different faces or facets on the other, and then look through it from the flat side to any object for instance, a pea-we shall then see as many peas as there are faces receiving the rays from the single pea. Such is a multiplying glass, or lens, which we may exemplify as follows:

H

Multiplying Glass.—In the annexed figure, A B is a lens flat

on one side, and cut into three faces on the other, C D E. F is the eye of the spectator, and G is a AF pea, the object looked at. The eye receives a pencil of rays direct through the glass at D, and sees the object just as it is. The pea G, however, sends also

a pencil of rays to the face C, and another to the face E, and these being carried through the glass, proceed to the eye. These various pencils of rays are represented in the cut by single lines. If, instead of using the term pencils of rays, we were to say that each face takes in the appearance of the object, the explanation would perhaps be more plain. Either way we describe it, the eye recognises three peas instead of one, and to all appearance at the places where we have marked them. It will be seen that the situation of the two supposititious peas, H and I, is determined by the angle of the upper and lower facet. That which deceives the eye, is the obliquity of the rays in crossing the glass at these points. The eye cannot look through these sloping sides, and then bend its vision to the pea in the centre; the vision travels in ideal lines at a straight slope to the two points where the supposititious peas are placed. Were the off-side of the glass to have a hundred facets, we should see any object we looked at through it multiplied a hundred times.

Magnifying Glasses.—The lens for magnifying is usually a piece of glass-as, for example, the eye of most kinds of spectacles-thick in the middle and thinner at the edges. In looking through this species of lens, called a double convex lens, the object, instead of being multiplied by distinct facets, is apparently drawn out or increased in size. In reading by it, the print seems larger than it really is. The annexed cut represents an eye looking through a magnifying lens at a small arrow, A B.

CA

АЖ

B

D

Fig. 2.

The edge of the lens is supposed to be towards us. We observe that the rays from the arrow A B, are embraced by the lens, and then bending through the glass at every place except the centre, converge to the eye. The eye, however, is deceived as re

spects the coming of the rays from the object to the glass. The vision, on the principle already explained, is made to embrace the space C D, and the rays within the limits of A B are seemingly drawn out to that extent. Consequently the arrow A B is to all appearance the size of an arrow C 'D. In the cut, for the sake of clearness, only three rays are marked, but rays, in reality, proceed from every part of the object, filling up the whole glass.

By holding the glass nearer, or more distant, we can limit or increase the divergence of the rays, and so regulate the magnifying power. There is a point, however, at which we can see the object most clearly, and that is called the focal point-that at which the rays concentrate.

Inversion of Images.-Lenses of the kind now described have

the image of the objects looked at. This arises from the crossing and interweaving of the rays, and takes place beyond the focal point. The principle of inversion may be illustrated by the diagram, fig. 3. A B C is an arrow, with the point uppermost, placed beyond the focus at F, of a double convex glass def. In virtue of the refractive power of the lens, the rays which proceed from A meet at a, and form an image of the arrow-point inverted; while the rays from C meet at c, and form a similarly inverted image of the feather part of the arrow. The rays proceeding from B, unite at b. As in the preceding cut, for the sake of clearness, only certain rays are represented; but in point of fact rays from all parts of the object proceed through the lens, and

F

hence an entire image is formed in an inverted position. Should the object A B C be brought nearer the lens," the image will be removed to a greater distance, because then the rays are rendered more divergent, and cannot so soon be collected into corresponding points beyond. To procure a distinct image, the object must be removed farther than the focal point F from the glass. In this exemplification, the object seems to be diminished; but if we make the small arrow the object, the larger one will be the image of it magnified.

Fig. 3.

Diminishing Glasses.-A glass to diminish the apparent size of objects is a double concave lens-that is, thin in the middle and thicker towards the edges. The rays in the case of this lens, instead of diverging, converge, or come together. A concave mirror shows the principle of this convergence, and diminishes the image of objects pictured in it.

Burning Glasses. When a double convex lens is held up to the unclouded summer sun about noon, the rays which converge at the focal distance from the glass produce a burning heat, and will set fire to gunpowder or any other readily combustible sub

stance.

TELESCOPES.

A telescope is a long darkened tube fitted up with lenses at certain distances from each other, and respectively of certain refractive power. The purpose of this instrument is to bring distant objects apparently near, and this is done by the combined powers of the lenses. Had the ancients been acquainted with the telescope, they would doubtless have degraded it to purposes of popular deception; it would have been one of the most valuable engines of the magician. The microscope, an instrument