I added the below two images and captions to Trombone History Timeline (19th century, 2nd half) and the collection, Backward Advances: Rear-Facing Trombones Throughout History.
1860—A drawing for the cover of the piano-vocal score for Jacques Offenbach’s operetta, Les deux aveugles, features a man holding a rear-facing trombone, with a similar trombone along the border nearby (see below image; public domain) (source: Wikimedia commons).
1883—New York: The Great Rival Advertising Shows to “Boom Up” Stocks, a print by Bernhard Gillam, is published in Puck (v. 14, no. 339). It shows three advertising sideshows, one of them represented by a man playing a rear-facing trombone (see below image; public domain).