A little delay…

We seem to be having a little delay in the posting of The Giant’s Shoulders #20.  I’m trying to figure out what’s up, and hopefully it’ll be published within the next day.

In the meantime, this seems to be a good time to beg for more hosts — we really need to fill up a few more months in the schedule!  Remember that you don’t have to be a historian of science to host — just someone with an interest in science and its history.

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4 Responses to A little delay…

  1. Mary D says:

    You may be just the one to answer this: If the spectrum’s perceived colors vary as a function of wavelength, then why can we mix two pigments and see, say, orange or green? Because the spectra of the pigments start out as a somewhat mixed bag, and get even more so. I think I am not thinking about this right. It’s the difference between the way we perceive colors in light and colors in pigments/dyes– most of our material world. How about filters used to create colored light for stage lighting, or sunglasses?

    • Hi Mary,

      I don’t completely follow your question, but let me take a stab at an answer anyway!

      A green paint pigment is not itself green, but rather it absorbs light of every other wavelength except green. The color that we see is the light that has been reflected, you might say “rejected”, by the material. When we mix two pigments together, the only color that we see is the light that gets rejected simultaneously from both pigments. You might start with a pigment that rejects primarily red, but also rejects a bit of orange, and a pigment that rejects primarily yellow, but also rejects a bit of orange. When you mix the “red” and “yellow” pigments, the only color that doesn’t get absorbed is the orange color.

      Things get more complicated because the human eye can interpret different combinations of wavelengths as the same color. The chromaticity diagram illustrates this idea somewhat nicely.

  2. mary says:

    Thank you! I was not thinking about this usefully and your response really helped. And then, you are right, our perception is another thing. I was reading the paper early in the morning and saw through a rent in the paper (cat was an active participant) a streak of a lovely pure blue. It turned out to be the white-with-a-tiny-bit-of-red wall, at that hour. Just looking at the wall, it didn’t ‘look’ blue because I ‘know’ what color it ‘really’ is…a whole ‘nother level of perceptual issues from that addressed in the diagram you helpfully attached.

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