The principal colours are divided into two series, the one comprehending what Werner terms bright colours, the other dead colours ; red, green, blue, and yellow, belong to the first ; and white. grey, black, and brown, to the second. They may also be divided into common colours, as emerald-green, ; and into metallic co lours, as gold-yellow, &c. The metallic culuurs are the most important as characters in describing minerals.
Arrangement of the colours.—The different charac teristic colours and their varieties pass into each other, forming suites of greater or less extent, in which the colours either differ more and more from the first mem ber of the series, as they approach the extremity, thus f wining straight series, or, after reaching a certain point of greatest difference from the first colour, again gradually approach, and at length pass into it ; thus forming circular series. In this way the eight principal colours pass into each other in the order in which we have already enumerated them, and thus form a straight series. The blue colour, however, after it has passed through green and yellow into red, passes from this latter colour by several intermediate varieties again into blue, thus forming a circular series or group.
In the system of colours, we do not introduce these various subordinate transitions and series, but simply arrange all the colours as they pass into each other, beginning with the white, and ending with the brown. The varieties of most of the different principal colours are so arranged, that their characteristic colour is plac ed in the middle of the series, and all those varieties that incline to the preceding principal colour arc placed immediately after it ; while those that incline to the next or following principal colour immediately precede it. This, however, is not the case with the white and grey colours; therefore the characteristic colours in those series do not stand in the middle ; on the contra ry, in the white it is placed at the beginning, and in the grey at the end.
I. Definitions of the different Varieties of Colour.