Letter | Published:

A True Spectrum Top and a Complementary One

Abstract

To make a true spectrum top—which is not copyright, so far as I know—take a disc of white paper, and one of black, of equal size. Spin the white one on a disc of cardboard mounted on a nail, and while it is spinning draw a small brush well charged with lamp-black water-colour paint, steadily and not too slowly from centre to circumference of the disc, thus describing a spiral line. Make a radial cut in each of the discs, and after interlocking them as in the well-known colour discs, place them on the top. We thus obtain a top in which the lines are spiral, and the relative sizes of black and of white areas are easily regulated by turning one disc to right or left, while the other is held still. If the lines be not too thin or too thick, and not too near together, and if the relative areas of black and white be adjusted suitably to the light, the top exhibits, when spun, broad bands of colour, each band containing all the colours of the spectrum in their natural order. The spaces between the lines should be not less than five times as broad as the lines themselves. The brightest effects are produced in my own case, by lamplight, with the areas of light and dark almost equal; by daylight, with the dark area about three times as great as the light. Other proportions, however, seem to give better results with other people.

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