Evoluzione storica delle misure orarie in Italia

Abstract

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