“Indigo” has been a prime element of the list for quite a long time. Whether it goes back to Newton or not, I don’t really know. I doubt if Newton would have insisted on it being there because he wanted seven colors. I generaly find thay claims of Newton’s mysticism – at least in his science – are overstated. He could go overboard on Biblical interpretation, but I think he kept his science straight.
“Indigo” was used as a bluish color more commonly a few hundred years ago than now, I think. Some people might have kept it in there for that mystical 7. I’ve always felt that the modern tendency to keep it in was the result of people wanting to give Roy a pronounceable last name. Withoiut the “I” in “Indigo”, Roy G. Biv doesn’t have a vowel in his last name.
As for the list being revised, who the hell would be in charge of such a thing? Who would enforce it? And what legal or practical point would there be? I’m hangin’ onto Indigo, myself.
This is stupid. It’s completely arbitrary as to how many colors you want to distinguish within the rainbow. If we get rid of indigo, why not ditch orange, as well, since it’s simply reddish-yellow?
Heck, let’s do away with violet, too, since it’s nothing but a reddish blue. Traditionally, it’s seven colors, and given that tradition being firmly established, that should be the correct answer.
Because school lies. Or because teachers are too lazy to explain to the little kids what ‘magenta’ and ‘cyan’ are, so they just say red and blue. Either way, it ain’t good for the little guys.
If you remember art class, whenever you mixed yellow and blue, the green you got never looked very good. It was always dark, and kinda brown. Mixing yellow and cyan would have worked quite a bit better. Look at the zip lock bags with the yellow and blue makes green seal, they didn’t use blue, they used cyan.
However, maybe the teachers don’t know better themselves. Once some kids asked what color would contrast most on blue paper. She directed them to the color wheel, and to find the color opposite of blue, which was orange. Had the color wheel been correct, it would have been yellow.
Hmmm. Not true. As a painter I usually mix my own colors, and buy only Red, Blue, Yellow, Black, and White tubes of paint. I’m usually able to get the color I need. I find, however, that if I need a bright fuschia or turquoise–which luckily I rarely do–I can’t mix that “neon” brightness in out of my primaries and I must buy a tube of fuschia or turquoise. Otherwise, any painting I’ve ever done with “natural” colors I’ve done with nothing but the classic primaries–Red, Yellow, And Blue.
I wonder if the radio guy wasn’t really looking for the basic color words: black, white, red, yellow, green, blue, brown, grey, orange, pink, and purple. Not all of those are in the rainbow, but maybe he was confused. Also note that neither indigo nor violet is a basic color word.
Actually primary colors of pigment are red, yellow, and blue. What you’re thinking of are the primary colors of light, which are yellow, magenta and cyan. That’s why the ziplock bags have cyan and yellow.
There are many elements beyond color in our perception of objects. “Gold” is not just a color but the specularity of shiny metal. As an example take an image of a gold object in a graphics editor and use an eyedropper to grab the color of one pixel. Make a bitmap of just that color. I guarantee it won’t look anything like what you think of as gold. It will look brown or like a skin tone or anything but gold. Same goes for skin actually, does a “flesh” crayola (yeah, I know they haven’t had them for decades) look like any human?.
To describe the suggested motivation as “mysticism” would be exaggerating. And the versions that circulate (Google on “Newton + indigo”), which turn scholarly speculation into a nice wee story, are simplistic. But an idea along these lines has been seriously discussed amongst Newton specialists, after being proposed by Penelope Gouk in 1988.
As a preliminary, we should note that there’s a common confusion in this area. Newton often refered to the likes of red, blue etc. as primary colours, but in a different sense to the modern usage. To him a primary colour was any shade obtained from white light through use of a prism, with the important property that it couldn’t further be divided by another prism. As we’ll see, while he often discussed how the spectrum obtained by use of a prism could usefully be described as being made up of a few colours, certainly by 1670 he also believed that this spectrum was continuous. This he contined to believe (see, for example, Westfall p213).
Gouk’s basic observation is that what subdivisions Newton mentions spectra as having shifts over time.
The private so-called Chemistry Notebook starts with a section Of Colours that’s plausibly datable to 1666. This assumes that there are really only two colours: red and blue. It also discusses the colours that can be seen using a prism. But Westfall (p171) points out that when it comes to naming these colours of the spectrum, he left a blank in the manuscript which he then didn’t bother to fill it. Just not a particularly important issue. When he does produce a list of colours, there are five: red, yellow, green, blue and purple.
He next touched on the issue in the Optical Lectures. As Lucasian Professor, he taught optics at Cambridge between 1670 and 1672, with a copy of his lecture notes being deposited with the university in 1674. This is a moderately thorough draft of his optical discoveries. In it, he describes those same five colours as being produced by refraction. (See the passage quoted by Hall, p100; but in an endnote, Hall points out that he also at first ignores purple and has blue as the end of the spectrum.)
Then, in 1672, his discoveries are announced to the Royal Society. The first letter includes the following passage:
(The paper is reproduced in Cohen, see p54; I’ve modernised the long-s.) Hall (n.7, p414) points out that this passage is actually quite ambiguous. Are there 5, 7 or infinitely many primaries? Whatever the precise meaning, one of the follow-up papers in 1675 has a diagram with the familiar sevenfold division of the spectrum clearly shown and labeled (Cohen, p193).
In the first edition of Opticks the key passage falls on p34 and is pretty clear:
(Again, I’ve tidied up the s’s.) Virtually all the other references to the matter in Opticks are consistent with this list, though there are exceptions, like the passage on p87: “the usual Colours of the Prism, red, yellow, green, blue, violet”.
Gouk’s more speculative observation is that the shift from five to seven coincides with the introduction of a related idea: an analogy with musical scales. The very purpose of that 1675 diagram is to illustrate how the divisions of the spectrum supposedly mimic the notes on a string. This gets more fully developed in Experiment VII and Proposition VI, Problem II of Opticks. Sepper discusses this in some detail, including noting that Newton’s scale differs slightly from the Pythagorean one. The suggestion is that he was forcing his observations of spectra to fit this analogy, possibly having to invent orange and indigo as extra divisions. However Sepper notes (n.11, p206) that counter arguments have been made: perhaps these two colours are more easily seen in the conditions Newton was looking at them in. (On a related note, Newton does say on p49 of Opticks that indigo and violet, being dark, can be hard to see in some circumstances.)
Of course, the Pythagorean notion of musical harmonies has a history that is partially mystical. But I don’t think this connection is terribly important, since I don’t think Newton was terribly mystical. Nasty tempered heretical Protestant literalists tend not to be. Yet I do suspect Newton is seeing evidence of God’s harmony in Creation here and, as such, this is a case where his theological and historical beliefs are influencing his science. And while only a small part of the text of Opticks, these passages are plausibly relatively central. Why? Because of his conception of light as involving vibrating corpuscules. A connection with his speculations in Queries 13 and 14 at the end of the book is pretty obvious.
But there doesn’t appear to be a smoking gun that forces us to conclude that he “invented” indigo.
Another approach would be to ask what other people thought were the colours of the rainbow in the period? But that’s a bigger, broader question. Still, FWIW Theodoric of Freiberg had distinguished red, yellow, green and blue in rainbows in the 14th century. And there’s a passage on p53 of Micrographia where Hooke implies that “the Colours of the Rainbow” are “Scarlet, Yellow, Green, Blew, Purple”.
Cohen, I. Bernard ed., Isaac Newton’s Papers & Letters on Natural Philosophy, Harvard, 1958.
Gouk, Penelope, “The Harmonic Roots of Newtonian Science”, in Fauvel et al. Let Newton Be!, Oxford, 1988.
Hall, A. Rupert, Isaac Newton, Blackwell, 1992.
Sepper, Dennis L., Newton’s Optical Writings, Rutgers, 1994.
Westfall, Richard S., Never at Rest, Cambridge, 1980.
OK, maybe this is a highjack, but I just remembered a question I’ve had for a long time.
I’ve been told on good authority that you ALWAYS see light approaching you at c, no matter what. If that’s true, how can the frequency be changed by the fact that you and the light source are moving relative to each other?
What, ALL of them? But there’s an infinite number of divisions in the spectrum, very few have names. It’d be easier to ask “What are the colours used in the character names in Tarantino’s ‘Reservoir Dogs’?”