5, 6, 7; the last of which is called a copper-red on account of the analogy it bears to the colour of that metal. No. 8 is an ochre colour, No. 9 a violaceous ochre, and No. 10 a violaceous fire-red.
According to Newton the first ring should be composed of
Blue, White, Yellow, Orange, Red.
I find neither blue, nor the tints placed after the white and designated as yellow and orange. It seems to me that the tints of Newton's ring may be defined easily enough. They differ essentially from yellow and orange, and are in reality nothing else than the blond and tawny colours of our scale mixed together. Of this we shall have a direct proof by compressing these seven tints into a space as narrow as that which they occupy in Newton's first ring: for as soon as this is done we see the orange-yellow[1] which succeeds the white in the ring make its appearance. The blond and tawny colours of the scale are very compound tints: they possess a certain fieriness on account of the red which enters into their composition, have a slight resemblance to the colours of gold and copper, and are very difficult to be imitated, because their composition is such as to remove them further than the others from the prismatic colours. In nature they are found particularly in
1. The hair of animals.
2. The feathers of birds.
3. The fibres of certain species of dry wood, such as the walnut-tree, the pear-tree, &c.
4. The beard of corn, such as wheat, barley, rye, &c.
5. The smoke at the top of a flame.
6. The decoctions of roasted grain, such as barley, coffee, &c.
7. The halo seen around the moon when overcast with fog or light clouds.
The colours which the clouds assume are in general
Black, or very pure ash-colour;
White, or very light ash-colour;
The colour of smoke or coffee;
Red, more or less fiery;
Blue, very deep, and sometimes approaching to violet.
These are exactly the tints that would constitute the first ring were we to include in it the first two colours of the second ring. The tints
- ↑ The absence of the blue does not affect the theory of the colours of thin plates: indeed I take it as a necessary consequence of the theory. All the homogeneous 'rings commence at the same place; namely, at the verge of the central speck. In this position the thin plate reflects rays of every kind, and this circumstance it is that gives the white without any trace of blue. It is perhaps to the contrast between the white and the black that we are to ascribe the illusion at the place where the two contrary appearances are produced.
