The clock is of a type known as a regulator.
This style of design minimises all factors that could reduce performance.
One method is to reduce the number of moving parts to a minimum,
so there is a wheel for the escapement with the seconds hand on it (bottom),
a wheel for minutes, (middle), and a wheel for hours (top).
This eliminates extra wheels known as motion work to operate the hands, and
reduces the friction.
The pinions will be of high count, say 20 teeth instead of 8 or 10 teeth,
the arbors will be jewelled (with end caps) and the escapement will be dead beat.
The seconds hand is kept small so as to minimise the weight on the bearings and the inertia.
The hours are for 24 hours, so the clock may have been adjusted to count sidereal
time, (Star time) instead of solar time. Sidereal time has 366.25 days in a year.
The clock should perform much better than a domestic clock.
cheers,
Neville Michie

Pretty nice, I've always wondered why clocks weren't designed this
way.  Hours last too long and estimating minutes from the hour hand is
minimally useful while seconds are too fast and mostly irrelevant for
human use.

Reading the time as so many minutes past whichever hour is very
natural and informative.

On Sat, 23 Nov 2019 09:29:09 +0100, Jean-Louis Rault f6agr@orange.fr
wrote:

-- kc0ukk at msosborn dot com

My idea is that for the time this was built and used, there was little or
no need for really
accurate time keeping in most astronomy work.  The high accuracy/precision
needs
really didn't arise until the beginning of what I'll call "modern
astronomy", which I'll loosely
define as the discovery of the first pulsar, or the first use of VLBI
(whichever came first).

I took the "Astronomy 101" course during my freshman year at UMich in
1965.  I just
now realized that I was basically 2+ years too early.  At the time I took
the course, the
text used was 10 years old, and it didn't seem to me that much was going on
in the field.
Little did I know what was soon to come ...

Dana

On Sat, Nov 23, 2019 at 6:12 AM Jean-Louis Rault f6agr@orange.fr wrote:

Hi

That’s a very unique piece of history. Hopefully you were able to get it.

Bob

Hi,

On a related note, some trivia that might be of interest.

The master pendelum clocks is still in their basement in Observatoire
Royal de Belgique, I've seen them. They have their dedicated
heating-system to help control the temperature, ovenizing the whole
basement building (the clocks are in a separate house within the
basement room.

Similarly the pendelum clocks of Observatoire de Besançon is still
there, except for one which is taken out, restored and in the museum.
The buildings there have a 3 m deep ditch around the buildings, so that
ground movements does not disturb observations, but the clocks are
deeper down into two separate rooms, so their temperature variations are
stabilized to some degree that way.

It's fun to see these things, many times things is still there and maybe
not operational, but for sure part of the history.

Cheers,
Magnus

On 2019-11-23 09:29, Jean-Louis Rault wrote:

Celestial navigation users might object to the notion that seconds are not
important.
That is, if you can find anybody still exercising that art.  In that arena,
folks are
taught to read seconds first, then minutes, then hours.

Depending on the latitude, one second can lead to something like 1/4 mile
position error.  So, realistically, one might tolerate a very few seconds
error
without exceeding reasonable error expectations, but certainly no more.

Dana

On Sat, Nov 23, 2019 at 9:03 AM Matt Osborn kc0ukk@msosborn.com wrote:

Hi Marcus

On 23/11/19 14:31,You wrote:

Very interesting. I've been looking at their website, and saw mention of
the planetarium,is there anything else there for the public, such as a
visitors centre or is it just the planetarium ?

[From the website, it looks very much like it is still very much an
operational scientific institution, and I wouldn't want to get in the
way of that, but I am in Belgium every year for the Formula One, and
always stop off in Brussels/Leuven and sample the local...hospitality
:)]

Iain

On Sat 2019-11-23T09:29:09+0100 Jean-Louis Rault hath writ:

If the purpose of the clock was to determine what time it was from an
astronomical observation then a second hand was not sufficient.
Determining the clock offset required some sort of graphical marking
of seconds that could be reviewed after the fact.

If the purpose of the clock was marking the begin and end of exposure
of a photographic plate then seconds were not very important, and the
hour was something that could be kept in the observer's head while
marking the log book, and in the dark the big minute hand was a big
help to a lone observer whose hands and nose were freezing while
guiding the telescope by eye and slewing it to the next target by
hand.

--
Steve Allen                    sla@ucolick.org              WGS-84 (GPS)
UCO/Lick Observatory--ISB 260  Natural Sciences II, Room 165  Lat  +36.99855
1156 High Street              Voice: +1 831 459 3046        Lng -122.06015
Santa Cruz, CA 95064          https://www.ucolick.org/~sla/  Hgt +250 m

Hi Iain

There are different institutions on the observatory site in Uccle near
Brussels (the planetarium is somewhere else) See
https://www.astro.oma.be/en/.

I have regularly some meetings with peoples of the Belgium Institute for
Space Aeronomy there, so i'm going to ask them if there is something to
visit for the public on this Uccle site. I'll keep you informed.

Jean-Louis

Le 23/11/2019 à 18:21, Iain Young a écrit :