Swing bridge

I went for a walk along the Forth & Clyde Canal today with Mummy and Daddy. We came to an old swing bridge that had been restored and I couldn't resist having a tinker with the mechanism. It's harder than it looks though ... good job I wasn't trying to get my barge through!

"To keep every cog and wheel is the first precaution of intelligent tinkering." 
(Aldo Leopold)