I have a Holton Clarke model long cornet with double functional tuning slides - built around 1911. I think it is only cosmetically justified. For a C-trumpet, the tubes on the valves would also have to be shorter to be in tune (mine are not replaceable with shorter slides). The first slide is after the leadpipe(about 8" into the horn) then comes a short piece of straight tube, a 180 degree bend and then the next slide. The first tuning slide is more than long enough to tune to "A" instead of Bb. Both have water keys and they only fit into their respective sets of slide receivers. I have seen various horns folded to make them shorter - maybe from the time when (almost) everybody wanted to play cornet because the trumpet was thought to be vulgar (check out the turn of the century wind band stuff or current british brass band - the cornet parts have much more black on the page than do the trumpet parts). Arban clearly distinguishes the superiority of the cornet (of his day) in his Grand Method. The short trumpet looked more like a cornet and for someone accustomed to having the bell that distance from their face it may have been easier to hear while playing. Crowmadic-can you post a picture?