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Greek and Roman dials were not horizontal or vertical flat planar dials, but
hemispheres, scafes or other projections of the sky onto a spherical or
conical surface. Planar dials came with the Islamic dials.
Only a short note:This is not true. The first Greek dials were plane equatorial
dials with equal hours. Karlheinz
The first planar dial with a polar gnomon was by Ibn al-Shatir in Damascus in
1371. This dial had temporal hours, equal hours based on noon, sunrise and
sunset, and Islamic prayer times, including reference lines to prayer times
when the sun was well below the horizon. For me this dial is the epitome of
sundials. It includes all the time systems in vogue at that time and for
hundreds of years before and after. They all existed and were in common usage
suited for different purposes. The question remains "Who is bringing the duck"
for dinner. Time is important. Don't overcook it.
Regards, Roger Bailey
Michael Ossipoff
Sent: Wednesday, July 29, 2015 11:57 AM
To: Roger Bailey ; sundial list
Subject: Re: Temporal Hours
Roger, thanks for the answer. Ok, I shouldn't say that as a fact without
having more information than I do. This is what I was implying or saying,
without really having much support for it:
"In Europe and the fertile-crescent region, in ancient, classical and medieval
times, before mechanical clocks (starting with Folliet-balance clocks) came
into wide use, Equal Hours were of interest, for the most part, only to
astronomers and astrologers. For ordinary civil timekeeping, for arranging
meetings, keeping schedules or other civil/social purposes, Temporary Hours
were preferred by pretty much everyone."
Were a fair percentage of people making their appointments and schedules by
Equal Hours in the times and places named in the above paragraph?
I'm not being argumentative--I really don't know.
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Thanks for reminding me about Temporary Hours lines on Flat Dials being
satisfactorily approximated by straight lines. I'd temporarily (no pun
intended) forgotten that. It was a question that I'd asked, and received an
answer to, when I first wrote to NASS.
Were Flat-Dials (for Temporary or Equal Hours) in use before mechanical clocks
were getting popular? What about _wide_ use? How early?
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Can anyone explain why the early, inaccurate inertia-controlled
Folliet-Balance clocks replaced the cheaper, more easily-made water-clocks?
Were those earliest, most inaccurate mechanical clocks significantly, or any,
more accurate than water-clocks?
Michael Ossipoff
On Tue, Jul 28, 2015 at 11:58 PM, Roger Bailey <[email protected]>
wrote:
Hi Michael and all,
Temporal or Antique hours co-existed with equal hours from way back,
thousands of years. It didn't take a technological device like a clock to
cause a change. A more interesting point is the portrayal of temporal hours,
12 unequal hours in the day on a flat sundial. It is easy on Greek/Roman
hemispheres but what about flat planar sundials. Is it sufficient to
calculate the points for the solstices and draw a straight line between
them? This works but is it right mathematically? To answer this question,
Fred Sawyer gave an excellent presentation on Antique Hours at the NASS
Conference in 2010 in Burlington. Was it really five years ago! Here is a
clip of the abstract from the NASS website.
"Antique Hour Lines: Fred Sawyer gave another excellent example of his
reviews of the history of complex mathematical concepts for sundials. In the
case of Antique Hour Lines, the question was “Are they straight lines?” For
millennia they were assumed to be, but the assumption was questioned by many
mathematicians. Proofs were offered by Ibrahim Ibn Sinan in the 10th century,
Christopher Clavius in the 16th, Hellingweth in the 18th and many including
Montucla, Delambre and Cadell in the 19th, offering proofs that the lines were
in fact curved. The various proofs tended to be empirical based on plotting
the results of individual calculation. Biot offered an analysis in 1841 and
Davies in 1843, but the problem was not fully solved until 1914 when Hugo
Michnik studied the curves for the equatorial sundial, providing a method to
come up with non-parametric equations for the curve for each hour. Fred then
presented the graphs of various hour lines at different latitudes and
inclinations. The curves were amazingly complex looking but the specific area
of interest, where a shadow would be projected was very close to the straight
lines of the traditional method."
This is why I belong to NASS, to read the Compendium and to go to the
conferences. Here we see solutions to problems we didn't even know existed.
Regards, Roger Bailey
From: Michael Ossipoff
Sent: Tuesday, July 28, 2015 4:47 PM
To: Dan Uza
Cc: sundial list
Subject: Re: Precision: the measure of all things
(I should clarify again that, for clarity, I like to capitalize _kinds_
of whatever sort of thing I'm talking about...such as kinds of sundials or
hour-systems, though I realize that that capitalization is probably not
officially correct.)
Another closely-related interesting question is the matter of what _kind_
of hours are used. Of course every book or article on sundials points out
that, before mechanical clocks became widespread, civil time was measured in
"Temporary Hours", which divided the day, from sunrise to sunset, into 12
equal parts, and likewise divided the night, from sunset to sunrise, into 12
equal parts.
Those books and articles nearly always imply or say that equal hours was a
new invention when it was adopted--that someone invented a new way to
designate time, and so it was adopted. Another frequent, and related,
statement or implication is that the Horizontal Dial was an innovation that
was came into use upon its invention because, before that, its possibility
was there, but just hadn't occurred to anyone.
But I read different. I read that Equal Hours were in use by astronomers and
astrologers long before they were adopted for civil time, and so they were
hardly a new invention at the time of their adoption for civil time.
In fact, look at a Hemispherium or Hemicyclium. Designed to read in
Temporary Hours, its hour-line, for a particular hour, crosses a different
Equal-Hours line, according to the declination. Whether those Temporary
Hours were drawn by calculation, or by empirical observation, it's plain
that it would have been obvious to the dial-maker that he was making the 3
p.m. hour-line cross different Equal-Hours lines at different solar
declinations.
One thing that I'm objecting to is that many of those books imply that
Temporary Hours are more primitive, and Equal Hours are something more
advanced that therefore, when invented, immediately replaced Temporary Hours.
Primitive? Rather, a lot more complicated and laborious to make. For
sundials, and likewise for water-clocks.
People should be impressed by the ingenuity and determination of early
makers of sundials and water-clocks, who devised Temporary Hours markings
and mechanisms for them.
As for the Horizontal Dial, of course it's for Equal Hours. That's what it's
convenient for. Sure, Flat Dials, including Horizontal Dials, and Polar
Dials, and Equatorial Dials, and others, could have likewise been made for
Temporary Hours, but they wouldn't have been easier to mark than a
Hemicyclium. So it isn't surprising if the Horizontal Dial came into use
around the same time as Equal Hours.
What I read was that, though Equal Hours were well known and used by
astronomers and astrologers, no one wanted them for civil timekeeping. Hence
the effort and ingenuity used to devise Temporary Hours sundials and
water-clocks.
But, when the mechanical clock was invented, and came into relatively wide
use (as tower-clocks, and in some homes), it was so much simpler to make
clocks for Equal Hours, that, as a result, Equal Hours replaced Temporary
Hours, for that reason of pure manufacturing-practicality.
(By the way, were the early mechanical clocks, the Folliet Balance
intertially-slowed clocks, without the fusee compensation, any more
accurate than water-clocks, which were much cheaper and easier to build?)
Temporary Hours surely made a lot of sense in agricultural societies, where
it must have been very important and practical for farmers to know what
percentage of the day remained. I don't advocate a return to Temporary
Hours, because, speaking for myself, it seems to me that finding what
percentage of the day is over, and how much or how little remains, seems a
bit pessimistic, and maybe not a good way to name the time of day. ...but
I realize that it had practical importance in agricultural societies.
Michael Ossipoff
On Mon, Jul 27, 2015 at 5:59 PM, Dan Uza <[email protected]>
wrote:
Hi everyone,
If you haven't already, you might want to check out the first part of the
documentary "Precision: the measure of all things". It's about the
measurement of time and length, featuring the topic of sundials. There's
an interesting theory about how the day got split into 12 hours because this
number is highly divisible (but why not 60?). I just watched it on Da
Vinci Learning.
Dan Uza
Romania
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