The bands or stripes in fig. 4, plate 1, when viewed through a prism, exhibit the colours represented in plate 2, fig. 5.

The date of the publication, 1810, is sometimes to be remembered.—T.

The forms in fig. 2, plate 1, when seen through a prism, are again intended to exemplify this. In the plates to the original work curvilinear figures are added, but the circles, fig. 1, in the same plate, may answer the same end.—T.