[EMAIL PROTECTED] wrote: > > To anyone who might know: > > Living in Tucson, Arizona, which has more minutes of sunshine > annually than any other spot in America, I became an amateur diallist a > few years ago. I > thought I'd put a question to you for your expert consideration. > For some time I've wanted to build a horizontal dial which reads > clock time directly. Normally, people who do this simply use equatorial > dials, as this is a simple process to merely adjust them to clock time. > Here is my theory: Could you look at it and tell me what you > think? What if (after properly calculating hour lines, and designing the > gnomon properly for your lattude) that you could mount the gnomon so > that it is properly oriented to the north but NOT ACTUALLY touching the > dial plate. That is to say, it sits a tiny fraction of an inch above the > dial > plate, anchored to an external point that lies to the north of the > gnomon. They could be for example, connected by a dowel rod. Now, > getting back to the dial plate itself. What if, at the junction of the > noon line and six-o-clock lines, we make a small hole...and then drive a > tiny rod into that hole so that the dial plate pivots around that point > on a base to which is attached? The point itself however, remains in the > same position relative to the gnomon. Could we not simply orient the > dial plate so that it reads clock time, knowing that it would have to be > adjusted every few days to account for the changing equation of time? > I've tested this theory by attaching a piece of thread connected to > a needle, driven the needle into the center of the noon/six-o-clock line > juncture so that the thread is flush with it, and then oriented the > thread to the north at the proper elevation to match Tucson's 32 degree, > 15 minute latitude. I'm using a paper dial template which pivots easily. > After adjusting the template to read mean time, I stick thumbtacks into > it to keep in in position to avoid the effects of wind. Although it > seems to be working like a charm, I thought I'd ask around, hopefully > encountering someone with the astronomical background to positively > confirm what seems intuitively to me to work fine. I'd appreciate your > consideration of this, as I've never heard of this method being employed > on a horizontal dial. Thank you, and keep up the good work! > > Tex Brashear
Dear Tex, As I understand you rotate the horizontal dial around a vertical axis. The dial plate itself stays horizontal. Is this right? Than your procedure won't work correctly. But it will work if you rotate the dial plate around the polestyle, the earth axis. The plate doesn't stay horizontal. Than you may make any correction to the time you want. You want the time in the next timezone? Rotate 15 degrees. You want to correct for EoT? Rotate the necessary angle. But always rotate around the polestyle. This procedure can be done for any dial, not only with a horizontal, but also with a vertical dial or a declining-inclining dial. About the mimutes of sunshine in Arizona; how lucky you are. Fer de Vries.
