NavList:

Rob van Gent, you wrote:
"most Rijksmuseum catalogers have a degree in history or art-history and are often unaware that octants and sextants are different instruments."

Are they? I would say that the words have shifted, and the word sextant now function as a superset term that applies to all instruments formerly distinguished as octants, quintants, even some instances of quadrants. We know that there was a sextant built into the hull of every Apollo spacecraft that travelled to the Moon. We know that aircraft were formerly equipped with periscopic sextants, and some navigators still experiment with bubble sextants. How many of these instruments would pass the old octant versus sextant test? Was the Apollo sextant really a sextant (by the original definition of the word)?

Scientific terminology matters and should remain stable, of course, and maybe that's a good way to define what qualifies as scientific terminology as opposed to common language. Scientific terminology, like, for example, the word "zenith" benefits from its constancy and stability. When I say "zenith" in celestial navigation, it means the point above every observer, 90° from the horizon. Is that 90° above the true horizon? apparent horizon? Small details are up for grabs, and I have to be careful to specify, if there might be any confusion over small differences. But when I say "zenith" I don't mean the peak of the Sun's altitude during the day, which is a "common language" usage (like the "zenith" of a person's career, used metaphorically). If someone else says "zenith" for the Sun's maximum altitude, I usually count that as confusing language in astronomy or celestial navigation, a dangerous offense against "scientific terminology"! It's dangerous because it is confused.

But is the word sextant scientific terminology? If I pick up a 19th century "octant" and start talking about it as a "sextant", is there any confusion generated? A few people with some expertise might be distracted, thinking that there is a nit to pick. But no one without that nitpicking knowledge would be misled in any way. It might be "interesting" to mention the word octant as a sidenote, a bit of color, but it would add little value. Sextant or octant, today it's all the same. The linguistic transition began decades ago, and now it is nearly complete. No mathematical theorems will collapse. No analyses of scientific observations will fail. The word sextant no longer calls for the stability of scientific terminology.

So I guess I'm saying, we can let the art-history majors win this one. ;)

Frank Reed