Dear Richard and Jack, You are both, of course, right on all counts...
> If I had a clock worth £60,000 and a replica > worth £500 I would take more care of the more > expensive original, wouldn't you? I am in the fortunate position of being the University Clock-Keeper and I do indeed take great care of "my" clock (whose value is of the order you quote). Fortunately most of the clock is indoors and is almost inaccessible. Anyone can look at the outside (the face and hands) which are as they were in 1679. [I have had them regilded once in 30 years.] If I were the custodian of a valuable sundial I would feel obliged to use a replica but I have misgivings... I suspect I shall be a lone voice here but, to me, the essential magic of a sundial is the way it comes to life when the sun shines on it. Sundials in glass cases are dead, even if they are of huge historical interest. What can be done? Let's ponder Jack's point... > Such a shame that we cannot have sundials > inside. > What we need is for somebody to develop a > motor-driven, geared apparatus that will > move an electric through a path that picks > up all the relevant celestial motions. No need for such complexity! A really simple approach requires curators of museums which contain sundials to appreciate that all the usual rules about lighting exhibits should be cast aside. Instead, most sundials should simply be lit by a single bright light which should be a near-point-source. Hmmm! At the dial, the source should subtend an angle of about half a degree! The next level of complexity is to have the light on some kind of track so that visitors can steer it around. When Jim Bennett was curator of the Whipple Museum in Cambridge (which is adjacent to where I work) I mentioned all this when he laid on a special sundial exhibition which lasted a few months. He set up a giant letter C whose two horns were aligned on a polar axis and could pivot. A sundial was placed half-way between the horns. A light was attached to the rim of the C and you could swing the entire C round the polar axis to simulate about 18 hours. The light could be moved to different points on the rim of the C so you could simulate different declinations. Of course, the light could sometimes be below the horizon. I have never seen this anywhere else but if you have to have sundials in museums this is the kind of thing that appeals to me! Sadly, I recognise that some colourings fade even in artificial light and sundials which suffer such sensitivity must, alas, remain in darkness. Frank King --------------------------------------------------- https://lists.uni-koeln.de/mailman/listinfo/sundial
