Hello Shadow Watchers(?),
This dial that came to the list as spam, but also
seems to give resolution of a time down to 1 minute.
I do not know how accurate it is but gennerally
"Pilkington & Gibbs" dials seem pretty professional.
http://cgi.ebay.com/aw-cgi/eBayISAPI.dll?MfcISAPICommand=ViewItem&item=1498358081
It also uses light instead of shadows for time.
Mike
36.9151 : 121.3539
--- David Pratten <[EMAIL PROTECTED]> wrote:
> Dear Walter,
>
> Greetings.
>
> There is another factor which limits sundial
> accuracy to about +/-22
> seconds. This is the variation in the value of
> Equation of Time from
> year to year within a leap cycle. See
> www.sunlitdesign.com/infosearch/sundialaccuracy.htm
>
> David
> www.sunlitdesign.com
>
> -----Original Message-----
> From: [EMAIL PROTECTED]
> [mailto:[EMAIL PROTECTED] On Behalf Of
> walter.jonckheere
> Sent: Thursday, 20 December 2001 8:47 PM
> To: [email protected]
> Subject: accuracy
>
>
> Greetings to all
> We all know that the atomic clock has the highest
> possible resolution,
> while for sundials 2 to 1 minute seems to be the
> best achievement. I
> have a feeling 1 second could be obtained
> considering what follows. ( I
> consider a second ideal as one can feel it, I mean
> it is a timespan well
> related to the human body, one second you live, the
> next you may be
> dead; it is also somewhat related to the heartbeat)
> Consider a
> horizontal sundial whith the 15 degrees hour lines;
> it is impossible to
> trace minute lines when keeping usual dimensions for
> the dial. However,
> if we go far away from the base point of the gnomon,
> the portion of the
> arc between 2 hours, becomes larger; so imagine we
> go to where 60 lines
> can be drawn between two adjacent minute lines and
> we keep only the top
> part of the line 11h59m59s and try to draw it on the
> ground related to a
> very accurate positioning of the local meridian.
> These data allow also
> to calculate the height of the gnomon tip. If both
> dimensions are
> feasable to realise, we would have the desired
> accuracy of one second;
> of course the positioning of the meridian is of
> paramount importance and
> probably the most difficult to materialise. ( is
> this a nice subject for
> a university ?) Of some important influence is the
> width of the gnomon.
> The indication of noon time is never accurate
> because of this width,
> while the shadow cast for the earlier hours, may be
> considered as a
> hairline and is thus more accurate, which means that
> the morning part of
> the dial is more accurate if the shadow hairline is
> taken into account
> for determination of the meridian. So in fact,
> sundials should have a
> gap at noon corresponding to the width of the
> gnomon, and the afternoon
> part should be calculated in function of the right
> hairline shadow
> related to a second parallel meridian. Very
> interested to read your
> comments Walter
>
=====
Mike DeAmicis-Roberts
phone: 831-636-0454
email: [EMAIL PROTECTED]
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