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
> >
> > --------------------------
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> > Politics Department
> > The University of Adelaide, AUSTRALIA 5005
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--------------------------
Peter Mayer
Politics Department
The University of Adelaide, AUSTRALIA 5005
Ph : +61 8 8303 5606
Fax : +61 8 8303 3443
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