by a reference to the law of imaginary colours. It is necessary to give a brief development of the principle of this theory.
Let any colour whatsoever be exposed to some given degree of light and let the eyes be kept steadily fixed on it for some time: if the eyes be afterwards closed we have the impression of a different colour, which though it is never the same for one tint that it is for another, is always the same for the same tint. These colours, in some measure the offspring of the real colours, are called imaginary by philosophers, and by others they are named fantastic or accidental. The following is a table of them:—
| Real Colour. | Corresponding imaginary Colour. |
| Red | Azure-green. |
| Golden | Indigo. |
| Green-yellow[1] | Violet. |
| Azure-green | Red. |
| Indigo | Golden. |
| Violet | Green-yellow. |
After this table I cannot do better in reference to the present topic than give the following extract from Venturi.
"The combination or succession of those colours which have such a mutual correspondence, that the perception of the one is followed by the imaginary sensation of the other, is agreeable and harmonious."
"Women of good taste know the colour of the trimming which has a good or a bad effect in combination with the fundamental colour of their dress. Leonardo da Vinci promised to give a table showing the colours which harmonize with one another and those which do not[2]: but he did not fulfill the promise, and no other painter that I know has pointed out precise rules for the harmony of colours. Several have observed merely that red combined with green has an agreeable effect; Newton apprises us that orange agrees with indigo; and Virgil was perhaps of the same opinion when he put this verse into the mouth of his Naiad,
Mollia luteola pingit vaccinia caltha.
"Mengs extols the union of violet and yellow; the same author says that the combination of red, yellow and azure is disagreeable[3]; but that each of them should rather be joined with the colour intermediate between the two others; the red with the green, the yellow with the violet, and the azure with the orange."
"These different opinions have their origin and foundation in the transitions from the real to the imaginary state, which, as we have seen, naturally follow the involuntary movement of the retina; so that the
