"These tints," Professor Nobili observes, "are disposed according to the order of the thin mantlings which occasion them; the colour of the thinnest film is numbered 1; then follow in order those produced by a gradual thickening of the medium. I cannot deceive myself in this arrangement, for the thin films which produce the colours are all applied with the same electro-chemical process. The battery, the solution, the distances, &c., are always the same; the only difference is the time the effect is suffered to last. This is a mere instant for the colour of No. 1, a little longer for No. 2, and so on, increasing for the succeeding numbers. Other criterions, however, are not wanting to ascertain the place to which each tint belongs."
The scale differs from that of Newton, inasmuch as there is no blue in Nobili's first series and no green in the second: green only appears in the third and fourth series. "The first series," says the Professor, "is remarkable for the fire and metallic appearance of its tints, the second for clearness and brilliancy, the third and fourth for force and richness." The fourth, he observes, has the qualities of the third in a somewhat lesser degree, but the two greens are very nearly alike.
It is to be observed, that red and green are the principal ingredients in the third and fourth series, blue and yellow in the second and first.
NOTE S.—Par. 485.
A chapter on entoptic colours, contained in the supplement to Goethe's works, was translated with the intention of inserting it among the notes, but on the whole it was thought most advisable to omit it. Like many other parts of the "Doctrine of Colours" it might have served as a specimen of what may be achieved by accurate observation unassisted by a mathematical foundation. The whole theory of the polarization of light has, however, been so fully investigated since Goethe's time, that the chapter in question would probably have been found to contain very