Plate 2, fig. 3.

Fig. 2, plate 1, contains a variety of forms, which, when viewed through a prism, are intended to illustrate the statement in this and the following paragraph.

Plate 2, fig. 5, left.

Plate 2, fig. 5, right.

This pure red, the union of orange and violet, is considered by the author the maximum of the coloured appearance: he has appropriated the term purpur to it. See paragraph 703, and note.—T.