Dear Mario,
> > the French hours are equal to astronomical hours.
I have some comments on your most interesting message but I would
like a proper expert to comment further...
1. LANGUAGE
> Here in Italy, by now from a long time, the term 'meridiana' is
> used as synonym of sundial.
To comment on this point I need some translations...
Italiano English
orologio solare sundial
meridiana meridian line (or noon line or noon mark)
gnomonista diallist
A pedantic Italian gnomonista would use the terms on the left
and a pedantic English diallist would use the terms on the right.
A meridiana is of course a special kind of orologio solare
but in Italy I find that `meridiana' is used not just as a
synonym for `orologio solare, it is used INSTEAD! If I use
the term `orologio solare' with Italian friends who are not
gnomonisti they think I am being very pedantic. Perhaps the
term `orologio solare' is too long for ordinary Italians!
In England, very few people who are not diallists would use
the term `meridian line'. Most people use `sundial' for ANY
kind of solar instrument.
2. FRENCH HOURS
> ... if you look for a precise description, without ambiguity, we
> cannot say that the French hours are the same as astronomic hours.
> French hours are the same hours used all over Europe from the half
> of the 14th century till now (we call them French just because
> Napoleon forced us to use them).
I think that it is impossible to give a precise description of
French hours without ambiguity!
You say...
> French hours are 24 equal hours parted in two group of 12, and
> they start to be counted from midnight up to noon (first group
> of 12), then from noon till next midnight (second group of 12).
Yes, I agree BUT, if we are being precise, this is still a bit
ambiguous. The problem is that `midnight' can be defined in
several ways:
A) It could be the moment of local inferior transit of the sun
in a particular place. This is OK for a sundial of course.
B) It could be the MEAN moment of local inferior transit of the
sun in a particular place. This is what French clocks used in
Napoleonic times and is probably what Napoleon forced on you!
C) It could be the MEAN moment of local inferior transit of the
sun at the French observatory in Paris.
D) These days, in Italy, it is midnight UTC+1 (or +2 in summer).
Does anybody know whether Napoleon understood the difference between
local sun time and local mean time? He very probably did. In his
day, sundials were used for setting clocks and he would surely have
known this?
I guess that when he imposed French hours on Italy what he did was
to use meaning (A) for sundials and meaning (B) for clocks.
Fortunately, Napoleon was not totally successful! There are still
numerous Italian-hours sundials in Italy AND there are still a few
Italian-hours clocks, especially in the Rome area.
Unfortunately, there seem to be only two people in the world who
are interested in Italian-hours clocks! I am one and Nicola is
the other! I hope I am wrong!!
Frank King
Cambridge, U.K.
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