Dear Jim, >An artist friend wants to make a sundial of a particular design, >which he describes as a "globe sundial designed by Thomas >Jefferson". the rough sketch he sent me suggests that the dial >face is carved on a spherical surface.
> -- if anyone recognizes this design and can direct me to a >source i may be able to make sure he doesn't waste time cutting >stone before we have a clear idea of the concept. It bears no reference to Jefferson, but in the Dover paperback 1996 reprint of Rorh, Rene R. J., "Sundials -- History, Theory, and Practice" p.114 there is a brief description of a 48 cm diam. spherical dial with a photo, Plate 44, and Figure 104 to show how a movable semicircle can aid reading. The equitorially aligned sphere sans any gnomon or other such aid can also be read by direct observation of the two points on the equator intersected by the boundaries of the illuminated hemisphere, according to the text. (The mean of the two shadow readings at the equator would give the hour angle, where the meridian of the sphere corresponds to the meridian of the place as zero.) Bill Maddux.
