On Tue, 1 Feb 2005, Larry McDavid wrote: > Another approach would be to place a painted steel plate on the inside > of the glass. If you then use a coated (anti-corrosion) rare-earth > magnet on the gnomon, there would still be significant attractive force > through the glass. Neodymium-iron-boron magnets give you the best > attractive force for the cost; samarium-colbalt magnets can be > "stronger" but cost substantially more due to the limited availability > of cobalt (not the samarium). Or, the magnet could be on the inside and > the steel plate on the outside. > > Larry McDavid
Or, put two disk magnets inside, and a matching pair on the outside. The rare earth magnets can easily be epoxied into place. Flowing a thin coat of resin over the entire (outaide) surface may be enough weatherproofing for them, as well. One disadvantage of placing one or more magnets opposite a sheet of steel is that they would have a tendancy to slip over time. A pair of dime-sized disks would "lock" to each other much more tightly. Having two pairs maintains position against rotation forces... Dave -
