Part 7

COLOURED SHADOWS.

Provide two lighted candles, and place them upon a table before a whitewashed or light papered wall: hold before one of the candles a piece of coloured glass, taking care to remove to a greater distance the candle before which the coloured glass is not placed, in order to equalize the darkness of the two shadows. If you use a piece of green glass, one of the shadows will be green, and the other a fine red; if you use blue glass, one of the shadows will be blue, and the other a pale yellow.

COLOURS OF SCRATCHES.

An extremely fine scratch on a well-polished surface, may be regarded as having a concave, cylindrical, or, at least, a curved surface, capable of reflecting light in all directions; this is evident, for it is visible in all directions. Hence, a single scratch or furrow in a surface, may produce colours by the interference of the rays reflected from its opposite edges. Examine a spider’s thread in the sunshine, and it will gleam with vivid colours. These may arise from a similar cause, or from the thread itself, as spun by the animal, consisting of several threads agglutinated together, and thus presenting, not a cylindrical, but a furrowed surface.

OCULAR SPECTRA.

One of the most curious affections of the eye is that, in virtue of which it sees what are called ocular spectra, or accidental colours. If we place a red wafer on a sheet of white paper, and, closing one eye, keep the other directed for some time to the centre of the wafer, then, if we turn the same eye to another part of the paper, we shall see a green wafer, the colour of which will continue to grow fainter and fainter, as we continue to look at it.

By using differently coloured wafers, we obtain the following results:

WAFER. SPECIMEN.

Black White. White Black. Red Bluish Green. Orange Blue. Yellow Indigo. Green Violet, with a little Red. Blue Orange Red. Indigo Orange Yellow. Violet Bluish Green.

BEAUTIFUL COLOURS OF MOTHER-OF-PEARL.

This substance, obtained from the shell of the pearl oyster, is much admired for the fine play of its colours. To observe them accurately, select a plate of regularly formed mother-of-pearl, with its surface nearly parallel, and grind this surface upon a hone, or upon a plate of glass, with the powder of slate, till the image of the candle, reflected from the surfaces, is of a dull reddish white colour, when it will glow with all the colours of the rainbow. The colours of mother-of-pearl may be communicated to soft black wax; and to clean surfaces of lead and tin by hard pressure, or the blow of a hammer. Or, dissolve gum arabic, or isinglass, in water, and allow it to harden upon a surface of mother-of-pearl, when it will take a perfect impression from it, and exhibit all the colours in the finest manner. Or, place the isinglass between two finely-polished surfaces of mother-of-pearl, and you may obtain a film of artificial mother-of-pearl, which, when seen by the light of a candle, or by an aperture in the window, will shine with the brightest hues.

WHITE LETTERS SEEN FURTHER THAN BLACK.

Paint the same letters of the same size precisely on two boards, the one white on a black ground, and the other a black on a white ground; the white letters will appear larger, and be read at a greater distance than the black.

ARTIFICIAL RAINBOW.

Observe the various colours which are reflected from the glass drops usually suspended from a lustre or chandelier, and you will witness a mimic rainbow. A rainbow may also be made by a garden engine, if the water be thrown high in the air, and the spectator stand between it and the sun.

FRINGE ABOUT A CANDLE.

Provide two small pieces of plate glass, moisten two of their sides with water, and put them together; then look through them at a candle, and you will perceive the flame surrounded with beautifully coloured fringes: these are the effect of moisture, intermixed with portions of air, and exhibiting an appearance similar to dew.

THE DOUBLE-COLOURED REFLECTION.

Provide a circular piece of coloured glass, and pierce its centre by means of a common awl, well moistened with oil of turpentine: encircle the glass with the fingers and thumb, hold it in the sunshine or the strong light of a lamp, and the following beautiful effects will be produced. If the glass be red, the luminous spot in the centre will be reflected green; if the glass be green, the spot will be red; if blue, orange; and if yellow, indigo.

LUMINOUS CROSS.

Place a lighted candle before a looking-glass, and there will appear a luminous cross radiating from the flame of the candle. This is produced by the direction of the friction by which the glass is polished; the scratches placed in a horizontal direction, exhibiting the perpendicular part of the cross, and the vertical scratches the horizontal part.

RINGS OF COLOURS ROUND A CANDLE.

Look at a candle through a plate of glass, upon which you have gently breathed, or over which are scattered particles of dust, or any fine powder, and you will perceive the flame surrounded with beautiful rings of colours. By using the seed of the lycopodium, or by placing a drop of blood diluted with water between two pieces of glass, the rings of colour will be still more finely exhibited. Round the luminous body there will be seen a light area, terminating in a reddish dark margin; this will be succeeded by a ring of bluish-green, and then by a red ring; these two last colours succeeding each other several times when the particles are of uniform diameter, as are the seeds of the lycopodium, each of which is but the 850th part of an inch in diameter.

SIMPLE AND CHEAP OPERA-GLASS.

In this new instrument, no tubes are necessary, as in the ordinary opera-glass; their place being supplied by a slender elastic conical spring of wire, into the upper extremity of which is inserted the eye-glass; the object-glass being fixed to the other extremity, as shown in the engraving. The two glasses must, of course, be kept parallel to each other when in use; which is very easily effected.

In using this opera-glass, rest the finger and thumb of one hand on the rim of the object-glass, B, whilst, with the thumb and finger of the other hand you hold the rim of the eye-glass, A. The spring tube may then be drawn out or shut up to very minute distances. Thus, the ordinary sliding tubes are superseded; nor is any external covering necessary, as the hand in grasping the instrument serves the purpose. If, however, a covering be preferred, a piece of silk may be sewn to the spirals of the spring.

This kind of opera-glass may be made very cheaply; it may be shut into a small space for the pocket, merely by pressing the object-glass and eye-glass together.

MULTIPLYING THEATRES.