Hi Roger, Patrick, Dave and all, My idea was to tilt the whole sundial, gnomon, base and all. It is as if it were remounted at a longitude where the local time was the same as the corrected time here.
In light of that, couldn't a wide gnomon standard horizontal dial be considered two dials mounted close to each other? In that case the tilt of the dial would still keep the two gnomons parallel to the earth's axis, thus correcting both. Well, of course it wouldn't be a horizontal dial anymore, but I wouldn't be that picky. The single rod gnomon that the balance of the dial hangs from would work nicely too, thanks Dave Edley. > Dave, Edley, and others, > > Thanks for the excellent suggestions! > > Edley's idea is simple and elegant. The only slight drawback I see is > that the base of the sundial has to be made thick enough to > accommodate the hinge. > > Dave's idea is also nice, and it avoids the need for a thick base. > Adrien Poncet liked to refer to his invention as a "no axis" telescope > mount (meaning that the polar axis was not a physical thing but was > implied by the 3-D geometry and degrees of freedom of the parts). > That is helpful in a telescope/camera mount because it means the > equatorial table can have a very low profile. But a sundial of this > type has a solid gnomon anyway, so why not make use of it, as Dave's > idea does! > > In a separate e-mail, Patrick Powers commented that the usual garden > sundial has a thick gnomon (in which you read the shadow from one edge > of the gnomon in the morning and the other edge in the afternoon). So > the gnomon theoretically needs to tilt *with* the base, rather than > being independently fixed while the base tilts under it. > > I'm trying to come up with the mathematical shape of a suitable cam > for controlling the base tilt in a sundial of this general type, > during the course of a year. So far, no luck. It may be easier to go > ahead and make one empirically. > > -- Roger > > ________________________________________ > >From Edley McKnight: > > A true equatorial mount is truly fine if you have one, A simple hinge > mounted in parallel with the earth's axis at some point below the > horizontal surface, allowing the dial to tip a little one way or the > other will allow adjusting for both Longitude and the Equation of > Time. One could consider the sundial to be a slightly slow or fast > clock and set it daily for the correct time, like any other clock. > (even daylight saving's time if the tilt is large enough) Mounting an > east west hinge below that would allow adjusting for errors in > Latitude as well. Setting up such a table is a fun thing to test > various designs or sundials found. I call it an "Latitude/Longitude > table". > > BTW, Even Pillar or Shepherd's dials made for other places seem to > work just fine locally when rotated on such a table, set for the > correct Lat/Long rather than dangled by their cords. Has anyone else > observed this? > > I still like Hendrik Hollander's cone gnomon design the best > currently. > ------------------------------------------------------------- >From > Dave Bell: > > A variant on that would be to use a long, straight shaft for the polar > axis and gnomon, letting the horizontal dial hang from the axis. The > adjustment would be very slight, barely noticeable as off-level... > ------------------------------------------------------------- > > --------------------------------------------------- > https://lists.uni-koeln.de/mailman/listinfo/sundial >
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