My doctoral dissertation used quaternions to describe spacecraft attitudes. My advisor was a stickler for not only appropriately citing references, but citing the most original (in the sense of oldest) references. This was something of a problem because the original references to some of the mathematical techniques I used were several hundred years old and not in English, and under the theory that a big part of the purpose of a citation is to help the reader understand the backgroud material this seemed a bit excessive. Nobody is going to learn French in order to read about Lagrange multipliers from Lagrange's original papers.
But for quaternions, it was easy: I actually cited the Brougham Bridge inscription. One cannot, of course, check the bridge out of the engineering library to check the citation, but clearly this was the original “publication” of quaternion multiplication.
If someone learned French to read about Lagrange multipliers from Lagrange's original papers, then they would be sorely disappointed: it was actually Euler who first used the Lagrange method! (And by some curious coincidence, the L/lambda could just as easily be a homage to Leonhard as to Lagrange...)
It used to be common in hard sciences and mathematics for English-speaking doctoral candidates to be required to show some aptitude for German or Russian. Maybe still is, dunno.
But for quaternions, it was easy: I actually cited the Brougham Bridge inscription. One cannot, of course, check the bridge out of the engineering library to check the citation, but clearly this was the original “publication” of quaternion multiplication.
My advisor finally got the point.