98 M. NOBILI ON COLOURS, AND ON A NEW CHROMATIC SCALE 



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, TVhite, 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 diffier essentially from yellow and 

 orange, and are in reality nothing else than the blond and tawny co- 

 lours of our scale mixed together. Of this we shall have a dii-ect 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* which succeeds the white in the ring make its ap- 

 pearance. The blond and tawny colours of the scale are very com- 

 pound 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, be- 

 cause their composition is such as to remove them further than the 

 others from the prismatic colours. In nature they are found particu- 

 larly 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, cofiee, &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 coloui's 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 con- 

 trast between the white and the black that we are to ascribe the illusion at the 

 place where the two contrary appearances are produced. 



