Note 74 — Chapter VI

On the Action of the Rays of the Solar Spectrum on Vegetable Colours: by Sir J. F. W. Herschel, Bart.

The proof of the continuation of the visible prismatic spectrum beyond the extreme violet may be witnessed in the following manner:—“Paper stained with tincture of turmeric is of a yellow colour; and, in consequence, the spectrum thrown in it, if exposed in open daylight, is considerably affected in its apparent colours, the blue portion appearing violet, and the violet very pale and faint; but beyond the region occupied by the violet rays, is distinctly to be seen a faint prolongation of the spectrum, terminated laterally, like the rest of it, by straight and sharp outlines, and which, in this case, affects the eye with the sensation of a pale yellow colour.”—Philosophical Transactions, p. 133.