It's obviously not rankine, seeing as it gives a conversion of ~30R = ~40C. Looks like its actually Reaumur: https://en.m.wikipedia.org/wiki/R%C3%A9aumur_scale
Actually makes it even more interesting, Wunderlich and his reaming to get some Reaumurs.
What were his actual measurements taken in and how accurate was his thermometer? And who's vaginas has it been in?
Curious I get flagged for pointing out the potential measurement inaccuracies and the errs of scientific reproducibility, all while having some humor.