John Carmichael wrote (replying to Chris Lusby Taylor):
>You're right! I realized as soon as I sent my message that a small diameter >floodlight with a wide beam would be better than a tight beam, because it >must illuminate the entire style and not just a portion of it. > A drawback with the "floodlight" scheme is that a very tall ladder will be needed unless you are only going to make use of the small bit of the gnomon near the origin. I know to my cost that big gnomons rarely have the small-scale accuracy required! Since what you are actually trying to do is to reproduce the method of a trigon (as Chris pointed out), why not use a real laser trigon. Bob Terwilliger has one on his webpages at http://www.shadow.net/~bobt/trigon/trigon.htm (based on a transit mechanism), and I published a cheap-and-cheerful small version in the BSS Bulletin October 99. Once the trigon is fixed to the style, and the hour angle set using the incorporated auxilliary dial, all you have to do is swing the laser on its declination axis and the spot will follow the humps and bumps on the ground precisely. If done at night, the laser spot is easy to see. If done in bright sunshine, you might need a red specular-reflector target and some red sunglasses to see the laser spot clearly. It's a shame you are so far away, as I built a "big" version of my trigon for the New Hall Oxford dial, but it didn't get fully used and I'm looking for another application!. By indexing the auxillary dial with 0.25 degree intervals, it gives 1 minute of time resolution. Regards, John ---------------------------------------------------------------------------- ------------------------ Dr J R Davis Flowton, UK 52.08N, 1.043E email: [EMAIL PROTECTED]
