Historical measurements of the Earth's magnetic field compared with remanence directions from lava flows in Italy over the last four centuries

A reappraisal of instrumental magnetic measurements made in Western Europe before AD 1750: confronting historical geomagnetism and archeomagnetism

“…We note that in Kircher (1641), the inclination value is 65°50′ on page 401, but 65°40′ on page 410. Nevertheless, regarding the distribution of the data, we do not see any reason to reject this particular datum, in contrast with doubt raised by Lanza et al (2005) and D ' Ajello Caracciolo et al (2011). The Italian dataset does not contain any other inclination value until the measurements made by Alexander von Humboldt in 1805-1806(e.g., Cafarella et al 1992.…”

“…3 but with no reference), which actually corresponds to the values expected at this location from the gufm1 model. It was calculated by Lanza et al (2005) to compensate for the very small number of Italian historical data between AD 1600 and 1805. This mistake therefore introduces a harmful interference from gufm1 into the SCHA model for the Italian region.…”

Comments on “Chronology of Vesuvius' activity from A.D. 79 to 1631 based on archeomagnetism of lavas and historical sources” by C. Principe et al., Bull Volcanol

“…Analysis of historical lava-flow units has revealed many cases where the ChRM direction deviated from the Earth's field. In the case of Italian volcanoes, a disagreement of a few degrees between the secular variation (SV) curve derived from historical direct measurements of the Earth's field and the lava-flow unit's remanence directions has long been pointed out in the literature (Rolph et al 1987;Incoronato et al 2002;Tanguy et al 2003) and has been shown to occur for practically all the post-1631 lavas; the ChRM direction of which can be checked against historical direct measurements (Lanza et al 2005).…”

“…In addition, there is no reason why rel should be constant in time over large distances. Analysis of historical data suggests that rel between Rome and Paris varied in the range of 1 • -3 • during the last centuries (Lanza et al 2005). The actual reference curve used for dating is not clearly indicated in Principe et al (2004), where they first refer to the Tanguy et al (1999) Mount Etna and the French (Bucur 1994) SV curves, before writing ".…”

Father Secchi and the first Italian magnetic observatory

“…In Italy studies measuring the Earth's magnetic field have a long history (Lanza et al, 2005;Meloni et al, 2007). The earliest documented measurements can be found from the mid-16th century on (Cafarella et al, 1992a;Cafarella et al, 1992b), while the first systematic observations of the magnetic vector began as progress was being made in geomagnetism in the 19th century.…”