I've recently encountered Jean Féry-Rebel's "Les Élémens". (Check out that wild opening; it's hard to believe it was written in 1737!)
In the fifth measure of the third staff, why does this descending scale include both F and E♯? (Notice that it uses the French violin clef, so the bottom line is G.) It's apparently not a typo; there are more E♯s in the instrument above this one and in the figured bass as well.
In recordings, this E♯ is clearly a half step lower than the preceding pitch, and thus E♮. Is this a byproduct of a particular tuning system? Is it some type of courtesy accidental so the performer doesn't play E♭ (the music did just cadence in B♭)? Or is it something else entirely?