FLASHES OF LIGHT UPON REVOLVING WHEELS.
PROVIDE a circle of card-board, six inches in diameter; divide it into sixteen parts, and paint them alternately red and black. Provide a second circle or disc of the same size, and paint on it, in large characters, the words “At rest,” on a white ground. Connect both discs with the simple apparatus for causing them to turn round, used in the construction of a toy windmill. Next fill a basin with water, and provide a few small pieces of phosphuret of lime: darken the room, hold the discs over the basin, and turn them round; let the phosphuret of lime be put into the water, and bubbles of light will rise to its surface. If they come up slowly, both discs will appear stationary during their turning round; but when the bubbles come up quickly, the black and red spaces will exhibit a dancing motion, and sometimes two black spaces will seem joined into one, to the exclusion of the intervening red, and vice versâ: the words on the second disc will also cross each other in various directions, when the flashes of light interfere; and, in both cases, confusion will be excited by an impression being made on the retina, before preceding impressions have departed.
DECOMPOSITION OF LIGHT.
Sir Isaac Newton first divided a white ray of light, and found it to consist of an assemblage of coloured rays, which formed an image upon a wall, and in which were displayed the following colours: red, orange, yellow, green, blue, indigo, and violet. Sir Isaac then showed that these seven colours, when again put together or combined, recomposed white light. This may be proved by painting a card wheel in circles with the above colours, and whirling it rapidly upon a pin, when it will appear white.
Light may also be decomposed by the following beautiful experiment: Form a tube about ten inches long and one inch in diameter, of paper, one side of which is of a bright blue colour. This may be done by wrapping the paper once round a cylinder of wood, and securing the edges of the paper with paste. The coloured side of the paper must be the interior of the tube. Apply this tube to one eye, the other being closed, and on looking at the ceiling, a circular orange spot will be seen, which is the result of decomposition: the white light from the ceiling enters the tube, the blue is retained, and the red and yellow rays enter the eye, and produce the impression of orange.