Before I read the reviews on IMDb for this film, I was still wondering "How'd they pull this off?" But now it all makes sense: the acrobats are lying on the floor, and the camera is pointed down towards them. It looks so realistic that some people I know actually thought it was real! I was starting to believe them, but then read the reviews, and it turns out I was right. Believe me, people can't balance up in the air like that.
That said, this film is very well done anyways. It features some "acrobats" doing remarkable feats. In fact, this reminds me of a film I've seen by Georges Melies, called "An Impossible Balancing Feat" in which a similar stunt is performed. This one is truly remarkable, due to its excellent hand-color. At only three minutes long it's fun and excellent for 1907. On a side note, Melies had used the same trick 5 years earlier in 1902's "The Human Fly" which was meant to actually make the audience believe a man could walk on the walls rather than perform amazing stunts.