Brown again

Jeremy (I recommend his blog highly) comments that he believes brown "does appear in the rainbow. It's just not one of the major colors that we organize colors according to, so we don't notice it except as a passing color." I don't think so.

Let me use an analogy to explain. Musical instruments, or the human voice, don't emit pure tones, with only a single wavelength and frequency. The violin string, or the trombone, vibrate at the frequency of the tone the musician is trying to produce, and also at higher frequencies, called overtones. The pattern of these is one of the things that enables us to tell a violin from a flute, or to tell different voices apart. If we could produce musical instruments that produced a single tone, we could still get combinations, by having more than one played at the same time, or, on a piano, by playing more than one note at once. We call these chords. They produce harmony.

Well, light consists of discrete waves/particles, each with a single frequency. Some of them, with particular frequencies, are red, for example. Others are yellow, etc. There aren't any single waves/particles that are brown, or white. Brown and white are the light equivalent of chords. For sound, the ear and the brain put two or more frequencies together to make a chord. For light, the eye and the brain put many colors together, and we perceive white, or a couple of colors together, and we perceive brown. Brown isn't part of the rainbow.