Evoluzione storica delle misure orarie in Italia



The present paper represents a research on the historical evolution,
in Italy, regarding the measurement of hours during the day. A few
cosmographical theoric recalls are offered to clarify how the problem
should be considered from the astronomical viewpoint. A review is then
made of the different chronometrical scales adopted in Italy, since Roman
times; then, later, in the High and Low Medieval periods down to
modern and contemporary times. All the different chronometrical scales
adopted, in their historical evolution, are investigated: temporary, equinoctial,
Italian hours, true local, mean local, civil, time hours a.m. and
p.m., mean Rome, Mean Central European, Universal and finally Universally
Coordinate, time hours; the intermittent adoption of legal summer
time, is recalled.
The importance of the problem is evidenced on account of the repercussion
that an inaccurate interpretation of the different time measures
given in historical times can have on geophysical events, and especially on an indexing of seismic events occurring in epochs prior to the
existence of radiosignalled time.
To illustrate the research, reference is made to the classical treatise
of Baratta «1 terremoti d'ltalia » (ed. 1901): possibility of alterations of
the fina lresults can be observed unless special attention is given to the
original chronicles. The alterations can even produce a date change
or a repetition, in the same catalogue, of the same event.
Reliability criteria are suggested for hour data in function of the
epoch of the event, as well as for the chronometrical scale employed in
evidencing said event.
In appendix some passages drawn from a study made by Serpieri
on the Rimini earthquake of March 18, 1875 that confirm tre difficulties
evidence are reported.
Some tables are also reported:
a table that gives the start of the clay for the calculation of Italian
hours at different latitude sand at different days of the year, prior to
and after the Gregorian reformation of the calendar, as well as the
corresponding time equations (App. E);
a table that gives the geoghaphical coordinates of the Italian
provincial capitals with the longitudes (referred to Greenwich and Rome)
expressed in time (App. D);
a table showing time periods where legal (summer) time was
adopted instead of solar time (App. B);
a table of intercalar seconds of Universal Coordinate time (App. A).

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DOI: https://doi.org/10.4401/ag-4733
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Published by INGV, Istituto Nazionale di Geofisica e Vulcanologia - ISSN: 2037-416X