For those out there who are unfamiliar with the Chair Gag (and I can't believe there are many of you) here it is, done pretty well, save for the whistle. I'm not sure of the clown or the show.
I was always afraid to do this one because I was worried one of the volunteers would drop to the floor. Jeff "Gordoon" Gordon was kind enough to teach me the gag in all of about 5 minutes and I've used it (without incident) when needed ever since.
Once, when we needed to cover some time, I stretched this gag to the breaking point and got 12 minutes out of it by using virtually every audience volunteer bit I'd ever seen or thought of. It worked out well but I wouldn't want to do it that way every night.