be expected. For music must take those which are most simple, and most consistent with each other.
Thirdly, Since the greens are respectively to the yellows, on one hand, as 9 to 8, and to the blues on the other, as 9 to 10, i.e. in the proportion of a tone; also to the reds, on one hand, as 4 to 3, and to the violets, on the other, as 3 to 4, i.e. in the proportion of a 4th; since farther, the yellows are as 6 to 5, i.e. thirds minor, to the reds, as 4 to 5, i.e. thirds major, to the blues, and as 2 to 3, i.e. fifths, to the violets; the blues as 5 to 6, i.e. thirds minor, to the violets, and as 3 to 2, i.e. fifths, to the reds; and the reds as 9 to 16, i.e. flat sevenths, to the violets; the difference of vibrations here exhibited may make the five foregoing colours appear distinct from each other to the mind, for the same reasons, whatever they be, as take place in sounds. For natural bodies reflect all these colours in great abundance, and in sufficient purity for this purpose. We may begin from green, as the most common of all. When this, as reflected by grass, suppose, has been sufficiently familiarized to the eye of a child, it is reasonable to think, that it may be distinguished from yellow and blue, and much more from red and violet, as reflected by flowers; also that these may be distinguished from each other. And it seems to me, that our fixed point ought to be placed in green, from the commonness and purity of the green of the third order, i.e. of grass and vegetables in general. For the same reasons one may expect, that the several shades of red, orange, green, blue, and violet, should be considered as several degrees of the same colour, viz. on account of the small difference of vibrations. At least this corresponds to the usual method of proceeding in other things. We distinguish great differences in our sensations by new names; but refer all such as are nearly related to the same. And thus the two foregoing suppositions furnish us with a natural reason for distinguishing the primary colours into five, viz. red, yellow, green, blue, and violet; which, agreeably to this, were all that Sir Isaac Newton himself distinguished the oblong solar image into for some time, as may appear by his optical lectures.
Fourthly, Since, if we proceed from the green to the yellow and red, on one hand, and to the blue and violet on the other, the ratios are the same, only inverted; and since there is a larger interval or ratio between the yellow and red, also between the blue and violet, than between the green and yellow, or green and blue; we may expect to have two more distinct primary colours corresponding to each other, and to the two semi-tones in an octave. And thus it is. Orange, and indigo, are sufficiently distinct from their contiguous ones, viz. orange from red and yellow, and indigo from blue and violet; and yet approach to them. And these seven colours, thus fixed, seem to be all that we can well call distinct colours amongst the primary ones, the intermediate degrees being referred to some of these seven, and
