From: utzoo!decvax!yale-com!brunix!gh Newsgroups: net.physics Title: Re: perpetual motion puzzle? Article-I.D.: brunix.1245 Posted: Mon Jan 17 08:32:49 1983 Received: Thu Jan 20 01:59:13 1983 References: fortune.726,sdcsvax.57 I saw one of these clocks with no apparent mechanism some years ago. If I remember correctly, the minute hand was fixed to the clear disk behind the hands. This disk was turned at the rate of one revolution an hour by a small motor in the base that drove the rim of the dial. The really clever part was the hour hand, which was quite loose, and you could push it about with your finger, and it would always return to the correct position for the current time of day. This was done by a counterbalance and a complex little system of gears in the hub where the hands met; as the minute hand / dial went round, this drove the gears in the hub and changed the angle of the hour hand relative to the counterweight (which of course always hung down). Graeme Hirst, Brown University Computer Science ...!{decvax, vax135}!brunix!gh