Dear Bob, Fun problem.
1. If I were setting the thing up, I would turn the existing disk so that the local longitude pointed up, not that of Greenwich. That way the observer can see at a glance "where in the world" he is, as well as the approximate time anyplace else in the world. There is a "blemish" on the longitude disk in your last photo; it looks as though it could be a locking screw. 2. To trace out the path of the sun, the hole would have to rotate around the axis, so I would want the "hour angle arc" to be similar to the one you have drawn, but rotatable. The hole would be in the slide, which moves up and down the arc at the middle +/- 23.5 degrees. 3. Either the hour scale must be attached to the hour angle arc and move under a fixed pointer or the pointer must be attached to the arc and the scale fixed. I like the idea of having the scale on the globe, since it reduces the number of parts. If the globe moved with the hole, however, it would be easier and more accurate to align the sun spot up with a line on the globe, rather than judging when the spot is round. On the other hand, if the globe is fixed, then it would be simpler and more elegant to read the time directly with the spot of light, rather than with an extra pointer. Furthermore, the "globe" can then sensibly be an actual globe, with a map of the world on it, rather than just a sphere. (But then why bother with a separate longitude disk?) Good luck, and lots of fun. Art Carlson
