Hi Peter, A way to determine how good this sundial is to make a model using balsawood and a magnetic compass and/or with large plastic bottle tops.
Roderick Wall. ----- Original Message ----- From: "Peter Mayer" <[email protected]> To: "Chris Lusby Taylor" <[email protected]> Cc: <[email protected]> Sent: Wednesday, March 10, 2010 3:35 AM Subject: Re: Would this dial work? > Hi Chris, > > Thank you, Patrick and Edley for your analyses. > I'm away from home and without access to references. I'm a bit > unwilling to > entirely dismiss the dial. I don't remember a discussion on this list of > magnetic azimuth dials. The Mayall's, I know, discuss them briefly in > their > book. In essence, as I recollect it, is that one lines up the dial with > the sun > using the sides of the box in which it is enclosed and then reads the time > from > the compass needle. That is, it is backwards from our usual practice and > expectations. If Viestur's dial _is_ a magnetic azimuthal dial, how far > off > would the equal angle dial be? > More broadly, does anyone have a better reference to the Magnetic > Azimuth > Sundial than that in the Mayall's book? > > best wishes, > > Peter > > Quoting Chris Lusby Taylor <[email protected]>: > >> Hi Edley, >> You are literally bending over backwards to try to justify this design. >> But >> the patent does say the time scale and shadow pointer are.."both >> revolvable >> about a common axis, said axis to be held in a vertical position during >> the >> reading of the dial" (column 1, line 31). So it is a horizontal dial, not >> equatorial. >> >> As for magnetic variation, it would be possible to allow for this to some >> degree in the placing of the time zone marks. But the picture makes clear >> that this was not in fact done, as they are all marked in 15 degree >> intervals. >> >> The patent goes on to claim the watch can be used "over the whole world >> without any difficulties depending on the number and the kind of the >> marks" >> which is utter rubbish as it is totally useless in the tropics, for >> instance. >> A southern-hemisphere version could be made by merely reversing the order >> of >> the hour numbers - perhaps this is what he had in mind. >> >> It is well known that you can very approximately find north by pointing >> the >> hour hand of a watch to the sun, mentally bisecting the angle between the >> hand and noon to find north-south. This invention merely reverses the >> process >> - given north-south, find the time. Why you wouldn't put a wristwatch >> movement inside the case instead of the sundial escapes me. >> >> Regards >> Chris >> >> >> ----- Original Message ----- >> From: Edley McKnight >> To: Chris Lusby Taylor ; [email protected] ; >> [email protected] >> Sent: Tuesday, March 09, 2010 5:16 AM >> Subject: Re: Would this dial work? >> >> >> Hi Peter, Chris, Patrick, and all. >> >> >> I agree with Chris if the plane of the watch is positioned >> horizontally, >> but from the patent, there is no regard taken for positioning the watch >> other >> than to magnetic north. If the central axis of the watch was made >> parallel >> with the earth's axis it would then function even better as an equatorial >> dial. Of course it would have to be held upside down in winter time and >> would have the times backward. One would also hope that magnetic >> deviation >> was not too far off. ( It's about 20 degrees about our area. ) The two >> threads function much like rotating a knife blade to minimise the shadow >> thickness. I wonder if many of them were ever made. >> >> >> Best Wishes! >> >> >> Edley. >> >> >> >> > Hi Peter, Patricket al, >> > I've had a brief look at the patent which, by the way, dates from >> > 1953. >> > It is, as you supposed, an azimuth dial. The two shadow-casting >> > strings, f, are horizontal, one >> > above the other. The ring, d, must be turned until their shadows >> > coincide, in other words when >> > they indicate the sun's azimuth. The "time" is then indicated on an >> > equiangular scale that is >> > carried by a compass needle, so 12:00 is always on magnetic >> > North-South. >> > So, as a sundial, it is very primitive. Its only sophistication lies >> > in the way the time shown can be >> > offset to indicate any desired timezone. But the time shown will be >> > accurate only at noon, as it >> > supposes that the sun's azimuth changes by 15 degrees per hour. >> > When I first saw the diagram I imagined it was a bifilar dial. I >> > think you really could make a >> > passably accurate portable bifilar dial in a very similar manner, >> > but this is not it. >> > Regards >> > Chris >> > 51.4N 1.3W >> > >> > ----- Original Message ----- >> > From: [email protected] >> > To: [email protected] >> > Sent: Tuesday, March 02, 2010 8:48 PM >> > Subject: Re: Would this dial work? >> > For those having difficulty accessing the URL a better one for >> > this would be: >> > http://www.freepatentsonline.com/2637108.pdf >> > >> > Regards >> > >> > Patrick >> > >> > >> > >> > -----Original Message----- >> > From: Peter Mayer <[email protected]> >> > To: 'sundial list' <[email protected]> >> > Sent: Tue, Mar 2, 2010 2:05 pm >> > Subject: Would this dial work? >> > >> > >> > Hi, >> > A while ago I came across US Patent 2637108 for a sundial watch >> > by >> > Viesturs(http://www.freepatentsonline.com/2637108). The patent >> > charmingly >> > suggests that it may be used 'for play and sport, where a good >> > mechanical watch >> > is endangered by pressure, sand and water, and therefore not >> > always adapted to >> > be carried around. As play and sport are mostly exercised >> > during sunny weather, >> > a portable sundial can well replace a mechanical watch on these >> > occasions". >> > As may be seen from the copy of the illustration which I've >> > attached, it >> > appears to be an equal-angle dial. It has a compass (label b)to >> > allow N-S >> > alignment of the dial. The shadow is cast by two vertical >> > threads (label f). >> > After some pondering, I have concluded that the sundial may >> > be a form of >> > magnetic azimuth dial, but this could well be wrong. >> > My question is: would this dial work? >> > >> > best wishes, >> > >> > Peter >> > >> > -------------------------- >> > Peter Mayer >> > Politics Department >> > The University of Adelaide, AUSTRALIA 5005 >> > Ph : +61 8 8303 5606 >> > Fax : +61 8 8303 3443 >> > e-mail: [email protected] >> > CRICOS Provider Number 00123M >> > ----------------------------------------------------------- >> > This email message is intended only for the addressee(s) >> > and contains information that may be confidential and/or >> > copyright. If you are not the intended recipient please >> > notify the sender by reply email and immediately delete >> > this email. Use, disclosure or reproduction of this email >> > by anyone other than the intended recipient(s) is strictly >> > prohibited. 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