I just added the following image and caption to 19th century timeline (1st half) and to the HubPages article, Backward Advances: Rear-Facing Trombones Throughout History.

1820-39—Rotterdam, Netherlands: A catchpenny print by T.C. Hoffers and A. van Alphen depicting various military instruments includes 2 rear-facing trombones, one with a dragon bell (see below detail; public domain) (Catchpenny Prints of the Dutch Royal Library).