The beam of light passing through the prism is decomposed, and the
spaces occupied by the colors are in the following proportions: Red, 6;
orange, 4; yellow, 7; green, 8; blue, 8; indigo, 6; violet, 11. Now,
if you paste a sheet of white paper on a circular piece of board about
six inches in diameter, and divide it with a pencil into fifty parts,
and paint colors in them in the proportions given above, painting them
dark in the center parts, and gradually fainter at the edges, till they
blend with the one adjoining. If the board be then fixed to an axle,
and made to revolve quickly, the colors will no longer appear separate
and distinct, but becoming gradually less visible they will ultimately
appear _white_, giving this appearance to the whole surface of the
paper.