Light; a course of experimental optics, chiefly with the lantern . byusing a confectioners glass jar 6 inches indiameter filled with Properly adjusted between theprism and the screen, this also will compound out of thespectral rays a white, though not perhaps very sharp, image ^ In cold weather the water should be slightly warmed, el?e conden-sation of moistnre upon the jar will interpose tedious hindrances togetting a good image. IV.] WHITE LIGHT A COMPOUND. 73 of the slitj and stopping off part of the spectrum will, asbefore, produce colour. Another beautiful and striking method is s
Light; a course of experimental optics, chiefly with the lantern . byusing a confectioners glass jar 6 inches indiameter filled with Properly adjusted between theprism and the screen, this also will compound out of thespectral rays a white, though not perhaps very sharp, image ^ In cold weather the water should be slightly warmed, el?e conden-sation of moistnre upon the jar will interpose tedious hindrances togetting a good image. IV.] WHITE LIGHT A COMPOUND. 73 of the slitj and stopping off part of the spectrum will, asbefore, produce colour. Another beautiful and striking method is shown in and 54. Get seven bits of looking-glass f inch wide by2 inches long. From a round wooden rod an inch diametercut discs, say | inch thick, as stands : to the top of each ofthese attach a bit of soft wax, and in this stick the end ofa mirror, so as to stand vertically as Fig. 53. Arrange asshown in Fig. 54, standing the mirrors on a piece ofblackened board, a, on a table-stand. First adjust thestand at such a distance that the rays from the prism p. Fig. 53. Fig. 54.—The Colours Recompounded. about cover the breadth occupied by all the mirrorstogether, and then take off all but one at the end, andadjust that so that it may reflect its colour to a good spoton the screen, s. Put on the second, and turn that till itsreflection occupies i/ie same spot; so of the third and therest. Note the changes of colour as we add colour aftercolour; till at last we have white. But take away—^suppress—any one colour, and again we get colour. Our next method depends on the persistence of visualimpressions. We see things nearly a second after the 74 LIGHT. [CHAP. exciting cause is gone—a long time, considering the ap^parently instantaneous character of all other light pheno-mena. Hold a slip of card in the diverging cone of lightfrom the lantern; it is a mere strip of bright white. Cutrapidly through the cone as with a sword; it appears awhite disc the size of the cone at the
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