Provide a wine-glass filled with plain water, which will keep off the heat so effectually, that the brightest sun may be viewed some time through it without any inconvenience. If a little black ink be added to the water, the image of the sun will appear through it, as white as snow; and when the ink is still more diluted, the sun will be of a purple hue.
BRILLIANT WATER MIRROR.
Nearly fill a glass tumbler with water, and hold it, with your back to the window, above the level of the eye, as in the engraving. Then look obliquely as in the direction E, a, c, and you will see the whole surface shining like burnished silver, with a strong metallic reflection; and any object, as a spoon, A C B, immersed in the water, will have its immersed part C B, reflected on the surface, as in a mirror, but with a brilliancy far surpassing that which can be obtained from quicksilver, or from the most highly-polished metals.
OPTICAL ILLUSION UNDER WATER.
Procure a large gallipot; place on the bottom, next the side furthest from you, a sixpence, and next to it, but towards the centre, a shilling; move to such a distance as will render the coins invisible; then let another person pour water gently in, and as it rises in the gallipot, it will cause both the sixpence and shilling to be seen, without your approaching nearer to the gallipot, or moving it towards you.
THE MAGIC WHEELS.
Cut out two card-board cog-wheels of equal size; place them upon a pin, and whirl them round with equal velocity in opposite directions; when, instead of producing a hazy tint, as one wheel would do, or as the two would if revolving in the same direction, there will be an extraordinary appearance of a fixed wheel. If the cogs be cut slantwise on both wheels, the spectral wheel, as it may be called, will exhibit slanting cogs; but if one of the wheels be turned, so that the cogs shall point in opposite directions, then the spectral wheel will have straight cogs. If wheels with radii, or arms, be viewed when moving, the deception will be similar; and however fast the wheels may move, provided it be with equal velocity, the magic of a fixed wheel will be presented.
Or, cut a card-board wheel with a certain number of teeth or cogs at its edge; a little nearer the centre, cut a series of apertures resembling the cogs in arrangement, but not to the same number; and still nearer the centre cut another series of apertures, different in number, and varying from the former. Fix this wheel upon another, with its face held two or three yards from an illuminated mirror; spin it round, the cogs will disappear, and a greyish belt, three inches broad, will become visible; but, on looking at the glass through the moving wheel, appearances will entirely change; one row of cogs, or apertures, will appear fixed, as if the wheel were not moving, whilst the other two will appear as if in motion; and, by shifting the eye, other and new effects appear.
These amusing deceptions were first experimented by Mr. Faraday. The simple apparatus for their exhibition may be purchased, for a trifling sum, of any respectable optician.