Although it's not trombone specific, bits of this doctoral thesis make interesting reading.

Howell, Jocelyn (2016). Boosey & Hawkes: The rise and fall of a wind

instrument manufacturing empire. (Unpublished Doctoral thesis, City, University of London)

Volume 1 [url]<LINK_TEXT text="https://openaccess.city.ac.uk/id/eprint ... ted%29.pdf">https://openaccess.city.ac.uk/id/eprint/16081/1/Howell%2C%20Jocelyn%20Vol%201%20%28Redacted%29.pdf</LINK_TEXT>

Volume 2 [url]<LINK_TEXT text="https://openaccess.city.ac.uk/id/eprint ... ol%202.pdf">https://openaccess.city.ac.uk/id/eprint/16081/2/Howell%2C%20Jocelyn%20Vol%202.pdf</LINK_TEXT>

Great find.

Very interesting details on the evolving pitch standards. Follow the money...

Although the Musical Times reported that Barnby adopted the lower ‘Continental Pitch’ for his St James’ Hall series of oratorio concerts in 1869,63 it was not until 1895 that a major change was initiated by the Queen’s Hall Orchestra, the first important permanent orchestra to be set up in London. It was founded by Robert Newman and relied on funding from Dr George Cathcart, an eminent laryngologist. Cathcart imposed the condition that low ‘Continental Pitch’ must be adopted because the high pitch in common use was causing serious vocal strain amongst singers.64