Hi Mac: you wrote: >Hi John, > >As I was walking my exercise miles this morning, I found myself >wondering why you are thinking of doing an azimuthal dial at all, >given the problems of dealing with either a short shadow or a very >long vertical post gnomon. Why not follow John Singleton's notion >(p. 51, BSS Journal for Feb 2000) and use your normal taut wire pole >style? > >Have I missed something in the discussion?
Maybe we all have. I think John Singleton's azimuthal will not work (except at noon, sunrise and sunset). I know this is a rather bold statement to make, but I think there is a general misconception that azimuthal dials can work with either a vertical gnomon or a polar axis gnomon as was originally suggested in an earlier discussion. This has always bothered me because it seemed impossible. If a polar axis works, then it would certainly solve the gnomon height problem. Rather than speculate, I did a simple experiment. Using a Spin drawing of an azimuthal for my location and an icepick for the gnomon, I quickly found out that the dial worked correctly when the icepick was vertical and became progressively worse as I tilted it towards the celestial pole. Now, I wonder what the theorists will say about this. I wish John Singleton had an e-mail, because I too wonder if I'm missing something. But since his dial is made for London, hopefully someone there will duplicate my experiment using the actual drawing in the BSS journal and let us know the results. John Carmichael p.s Sorry I already broke my promiss not to discuss azimuthal dials any more, but I couldn't resist this Luke's question!
