Hi Tony - Members, Tony Moss wrote:
> I'm all too familiar with the problem but not at all familiar with a > 'ridge' dial. Can you describe in more detail please Edley? > > Tony Moss > There are a number of ridge dial types, but they are based on the following. a. Taking an equatorial dial, make it into a set of dials that are in the same place, yet each only marks out a small interval of time/angle. Each of those now separate dials can be slid up our down the polar axis independently and continue to function properly. b. If they are spread out keeping the time interval between them even they will express curves of angle/time. The ridge guide I had in mind is a section of one where the noon point is held still and the other hours moved (north in the northern and south in the southern hemisphere) Thus creating two curves that will mark out the proper times before and after noon when the shadow of the gnomon falls on them. The "ridge" comes from filling in the area between the cylinder, the gnomon and these curves with a solid. Time is measured by where the shadow is fully on this solid surface. ( There are modifications to this also ) [ Those familiar with it can see that this is the same as a "two knife cut dial" with the area above the cuts removed. ] c. When placing this on to (for instance) a horizontal dial, the noon point is placed where the gnomon touches the horizontal and the other times spread out to agree with the the hour lines already in place. d. If only the ridge hours of say 10 AM to 2 PM are used and the edges truncated vertically beyond this point then the other hours are told as usual by the shadow of the gnomon. Noon is told by the vertical edges as a shadow plane clock and the hours from 10 to 2 are told by the ridge dial. ( This makes a very sturdy construction that could even be cast into the surface of a dial ) ( 11 AM to 1 PM is probably too sharp for many applications ) e. The area beyond the old length of the gnomon can be capped by a portion of a dome or by just a flat surface. Of course, for new construction, a full ridge dial, even stretching out the hours from early south to late north can show all the hours and is equivalent to a "single knife cut" dial with the areas above the cut removed. Other more decorative dials, with the angles properly formed can be sections of ridge dials that incorporate lettering or other design elements. ( individual equatorial time point dials can even be duplicated, injecting straight sections ) If this explanation isn't clear, I'll try making up some drawings, models, and posting them on my site. Enjoy the Light! Edley McKnight [43.126N 123.527W]
