[inevitable soundtrack]

This is a quick weekend note to offer a little distraction from the various travesties being wrought on American science (and much else).

One of my favorite (minor) genres in the history of science are stories of what might be thought of as useful errors. And in that one, I particularly love the story of the great physicist James Clerk Maxwell’s public display of what is often considered the first color photograph.

This is an anecdote that has given joy to a lot of people in and around the history of science, especially that of physics. That’s partly because Maxwell is at once a giant in the field—arguably, the most significant theorist between Newton and Einstein—and was, by all accounts, one of the good guys, someone a biographer can spend a lot of time with and feel that they’ve been in fine company. So it’s fun to see him make a mistake (perhaps better, be lucky); even the great ones can mess up! And because he is easy to root for, it’s also nice that the error didn’t get in the way of what he was trying to accomplish.

So what did Maxwell do?

The just-the-facts-ma’am version of the story is that in 1861 Maxwell gave a lecture at the Royal Institution (one of the great monuments to public engagement with science) in which he displayed this image:

That’s the famous Tartan Ribbon, an image created by Maxwell’s collaborator, Thomas Sutton.

For Maxwell, the significance of the image was the argument it helped him make in favor of the claim that the full color range that the human eye can perceive could be built out of three primary colors—an idea first proposed by Thomas Young  almost six decades earlier. Maxwell advanced Young’s thinking (and that of Hermann von Helmholtz, who built on Young’s work) when he provided a mathematical account of the three color hypothesis.

The tartan ribbon experiment was an empirical follow-up to that work of theory. The experimental problem to be solved was how to create a multi-color image out of the monochromatic photographs of the day. That’s where Sutton came in.

Sutton was one of pioneers of the early age of photography. What he did to create an example of Maxwell’s conception of color has been described in detail in a Scientific American article from 1961, written by Ralph Evans, one of a team of Kodak scientists who recreated the original experiment. Sutton first created three filters by dissolving metallic salts in water that he then placed in glass vessels. Each dissolved compound produced a different color: red, green and blue. He then photographed the ribbon through each filter, capturing the images on silver iodide emulsion. He printed the three images on glass to create transparencies. When Maxwell delivered his lecture, those three slides were illuminated with the appropriate shade of light—red for red and so forth, and projected to form a single colored image to astound the audience.

So far so good. Where’s the error?

Well…none of it should have worked. As Evans writes, the silver iodide emulsion Sutton used is only sensitive to light with short wavelengths—blue light. It can’t “see” red or green hues, and whatever was captured on the negatives shot through those two filters it wasn’t what a naked eye would have seen as those colors in the ribbon itself.

What happened? When the Kodak researchers tried to figure that out, they recognized that both their film stock and Sutton’s original plates could record not just blue light, but ultraviolet as well—electromagnetic radiation invisible to the human eye with wavelengths even shorter than what we perceive as blue. Even better, Sutton’s red and green filters were sensitive to different regions of the ultraviolet slice of the spectrum. Also, as Evans speculates, some red dyes reflect ultraviolet light as well as what we see as red—which means that (assuming the tartan ribbon’s red swatches were colored with the appropriate dyestuff) Sutton’s procedure would detect the red regions in the photographic subject even though it was only picking up an ultraviolet signal.

All of which is to say that the ground-breaking photograph was an accident. The tools he and Sutton had available should not have been able to achieve what they wanted; it did because the emulsion and the filters possessed unexpected and at the time unknown properties that allowed the expected result to emerge. The Tartan Ribbon image might be better described as the first false-color photographic image ever made. Except, of course, that the point it made was correct: Maxwell’s three color argument does indeed describe a part of reality.

I’ll let Evans have (almost) the last word:

Be that as it may, the principle devised by Maxwell and put into practice by Sutton was a valid one for producing a color photograph. And because of the fortuitous circumstances we have described, the experiment worked, allowing Maxwell to invent three-color photography almost 15 years before there were sensitizing dyes that would have made his experiment “possible. “

One more thing:

I hope anyone who has read this far has had fun with this little story of serendipity. It has certainly given me pleasure for a long time—but as I revisited it this weekend, I find that along with the fun of catching out a great one in a error, it has a bit of a somber cast to it. The last two weeks have seen a sustained attack on US science mounted by the Trump/Musk administration. A lot of damage has already been done, and if the moves both made and announced go unreversed, that harm will become catastrophic.

In that context, the story of this scrap of ribbon contains an important message: Maxwell’s mistake was a productive one. He got to a true fact: three color imagery can produce a powerful representation of reality, confirming both theory and prior observation. That’s what science does: imperfectly but with great power make incrementally more sense of the world around us. Gutting our ability to do that work will not just deprive us of the fun of such insights—think all those glorious images (in spectacular false color) captured by the Hubble and Webb telescopes, for example—but will also limit (cause us not to find) the knowledge vital to human flourishing that would otherwise have emerged.

There will be a lot more to say—and to fight to protect—in the coming days and weeks. Alas.

This thread is as open as a shutter on a deep space observation.

*If you’re so moved, subscribe! I’m aware of the disagreement on the use of Substack as a platform. My response is to offer Inverse Square as a free site. Barring unforeseen stuff, all content there will stay free. It is part of my likely feckless attempt to build a more sharply defined online presence in support of my public writing. Also I don’t think I’ll mirror everything, but if there’s anything I think might particularly appeal to our community, I’ll try to be sure to get it up here as well.

Image: Thomas Sutton and James Clark Maxwell, Tartan Ribbon, 1861