Perhaps we should cease the wild speculation regarding Weidinger and the key of the Hummel and look at some facts. First, the Hummel *was* originally in the key of E Major, regardless of any speculation otherwise. The New Grove work list in the article on Hummel *does* list the work as the Trumpet Concerto in E-FLAT, but it also lists the source consulted for the works list as the Leipzig publication from 1957, NOT the original manuscript. Joel Sachs obviously didn't do careful homework on this point, so we learn a lesson here: just because it's in the New Grove (shudder to think . . .) doesn't necessarily mean it's correct. In Tarr's article on Weidinger, also in the New Grove, he refers to the Hummel Concerto in E. Contradiction in the New Grove? Sure enough. Obviously Ed Tarr has looked at the original manuscript (see the preface to his edition of the piece in E), whereas Joel Sachs did not.
Regarding the "commission" of the work, I'm not sure what the person posting meant when they said "non-resident composer" when referring to Hummel. Hummel was born in Pressburg (what is now Bratislava, which is only about an hour from Vienna), which was at that point part of the Austrian Empire; he was, therefore, Austrian, as was Weidinger, and worked largely in Vienna, as did Weidinger. The Hummel Concerto was written about a year before Hummel became "Kapellmeister" (I use quotations because Haydn kept the title of that post even after Hummel took over) at Esterhazy, and was in very close contact with Haydn, especially between 1795 and Haydn's death in 1809. Hummel was, therefore, likely very familiar with Weidinger's instrument; let us not forget that while the Haydn was written in 1796, it was not premiered until 1800. While the connection between Hummel and Weidinger is not as clearly documented as that between Haydn and Weidinger, given what we know about Haydn's relationship with Hummel, we can safely assume that Hummel was not just blindly writing a commission for someone of whom he had no knowledge. The Hummel Concerto was premiered at Esterhazy on January 1, 1804; Hummel became Konzertmeister (read Kapellmeister) at Esterhazy in April of that year.
As far as the instrument itself is concerned, Hummel wasn't just writing a random trumpet piece, he was writing specifically for Weidinger and specifically for his instrument. The speculation that Hummel misunderstood and composed the piece in E rather than E-flat is simply not plausible. Weidinger was continually experimenting with his instrument and tried several keys before his death, and Dahlqvist, in his monograph on Weidinger, states that the lower tessitura of the Hummel (as low notes are easier to produce on a higher instrument) suggests that Weidinger had a new instrument, perhaps with a wider bore. The chain of inverted mordents in the Hummel is also so similar to those in the Haydn that it again points to a close connection between Haydn, Hummel, and Weidinger; thus Hummel must have known the instrument for which he was writing.
Matthew P. Woodward