116 M. NOBILI ON COLOURS, AND ON A NEW CHROMATIC SCALE 
pure: they are all composed of several others. Hence arises a law of 
brightness different from that of the prismatic colours. The clearest 
on our scale are, 
Ist, The azures ............cc000s Nos. 16 and 17. 
9nd; Theblondsiis23.) eee land 2. 
3rd, The yellows.............. dads 18 and 19. 
The most obscure tints are Nos. 10, 11, and 12, in which the violet and 
blue predominate. 
Depth. 
Depth, or intensity, and brightness are very different qualities. No 
one indeed confounds the intensity ofa fine red with the brightness of a 
fine yellow. In the scale of the latter quality the white occupies the 
first place. A bright tint may be considered as a mixture, in which 
there is a little colour with a great quantity of white light; and, vice 
versd, a strong or deep colour, as a mixture of much colour with a little 
white light. Painters therefore when they want to give brightness to 
their colours add white, but when they want to increase their intensity 
they add a different colour. 
The most intense colours of the scale are the lakes, especially No. 28 
and No. 29. The feeblest are the azures No. 16 and No. 17, the blonds 
No. 1 and No. 2, and the yellow No. 18. 
Some colours strengthen each other; some have no such effect. Thus, 
for example, the red of the spectrum combined with the violet forms 
a very beautiful lake, which is a much more vivid red than that of the 
prism. The same red combined with the green forms a mixture which 
possesses more intensity. The tints of the scale include all the pris- 
matie colours, and their strength depends exactly on the proportion of 
the elements which enter into their composition. . The lakes. abound in 
red and violet, which are the two colours that give most depth to each 
other, as if one were the octave of the other. The sky-colours are too 
feeble, because with the exception of the blue, which they contain in a 
quantity rather excessive, the colours which enter into their composition 
will, when mixed, produce only white. 
It is not strictly true that the intensity is in the inverse ratio of the 
brightness, because the more obscure tints Nos. 10, 11 and 12 are 
less intense than the lakes Nos. 28 and 29. Nevertheless there is a 
manifest relation between the two qualities; for it is certain that the 
feeblest colours are among those of the brightest class, and the most in- 
tense among those of the most obscure. 
Thin plates according to their different degrees of tenuity reflect dif- 
ferent colours ; either these reflected colours are such as mutually to 
strengthen each other, so that there results from them a strong tint ; 
or they do not strengthen each other, and the result of this is a white 
which predominates in the tint. Thus, the cause which generally renders 
