106 M. NOBILI ON COLOURS, AND ON A NEW CHROMATIC SCALE 
tions are far surpassed by those of the thin laminz. If we imagine one 
of the colours of the laminz combined with another, we have the im; 
pression of a new tint. The combinations that may be obtained in this 
way are almost innumerable, and, it will be said, need well be so, in 
order to match the variety which nature exhibits. Such is our opinion 
too; but we shall not attempt to conceal the difficulty presented by. 
the fact, that several of the natural colours, especially those of the me- 
tallic substances, have but a very slight resemblance to the colours of 
thin plates, among which it were vain to seek, for example, either the 
yellow of gold or the red of copper. The colours of the plates which 
approach them most nearly are found among the first seven or eight 
tints of the scale. The gold might be placed among the blond colours, 
and the copper among the tawny; but the difference is still so striking 
that it would be unwarrantable, before it is accounted for, to put entire 
and implicit confidence in the principle of the lamine. 
This principle requires, as a primary condition, that the integrant 
molecules of bodies should be transparent. It is true that almost all 
bodies reduced to a certain degree of tenuity are permeable to light ; 
but it is equally true that the existence of a single body perfectly opaque 
and yet exhibiting a colour, would render it necessary to look for an- 
other principle of coloration besides Newton’s, which is applicable only 
to diaphanous substances. 
In my Memoirs on the electro-chemical appearances, I have shown 
that they are not exclusively produced by one of the poles of the pile, 
The appearances which constitute the chromatic scale are due to the 
electro-negative elements of the solution (oxygen and acid), which being 
transferred by the current to the positive pole, are there spread out 
into thin transparent films, from which all the colours of the scale arise, 
The electro-positive elements (such as hydrogen and the metallic bases) 
are, on the contrary, transferred to the negative pole, and there depo- 
sited in layers which never produce the colours of thin plates. Here 
it is impossible to mistake in any case, but more particularly in respect 
to the solutions of certain salts with a base of gold or of copper, which 
produce negative appearances invariably of the same colour as the me- 
tallic base. It cannot be said in this case that the substance has not 
been brought to the degree of tenuity necessary to render it transparent. 
The electro-chemical layers commence with the first degree of attenu- — 
ation at the positive as well as the negative pole... If the layers of the 
positive pole produce the ordinary colours of the plates, while the oppo- 
site pole completely fails to present any other than that of the metallic — 
base, it necessarily follows, either that these bases are perfectly opaque, 
or at least that their transparency is so imperfect as to render it im- 
possible to apply the general laws to them, unless with very important — 
restrictions. Indeed we have here a decisive proof that the colours — 
