GIUSEPPE FOLGHERAITER: THE ITALIAN PIONEER OF ARCHAEOMAGNETISM

The history of the science of archaeomagnetism conventionally starts in 1600 with thepublication of William Gilbert's monumental work De Magnete, but the theoretical basisof this scientific field has to be positioned at the end of the nineteenth century. In Italyat that time, a number of scientists such as Giambattista Beccaria, Macedonio Melloniand Silvestro Gherardi, were working on magnetic field characteristics and their workvariously contributed to the early study of Earth and rock magnetism. A majorcontribution to the birth of paleomagnetism as a science, and archaeomagnetism as adating technique, was produced by Giuseppe Folgheraiter (1856-1913) by means of hisresearch on the magnetic properties of volcanic deposits and his attempts to date ancientpottery of different epochs based on the magnetic properties of clay materials. Initially,Folgheraiter studied the rock magnetism of the volcanic rocks of Latium where hereplicated the findings of Macedonio Melloni, who had studied Vesuvius lavas, andfound that volcanic rocks are affected by a permanent magnetization. In addition,Folgheraiter verified the discovery by Filippo Keller of the Punti distinti. Folgheraiteralso made the innovative proposal that lightning strongly influences the magneticproperties of lavas resulting in magnetic disorder. The main analytical effort ofFolgheraiter at the end of the nineteenth century was dedicated to the study of thevariations of magnetic inclination in different epochs as registered in archaeologicalpottery. He produced archaeomagnetic sets of analyses on 191 samples grouped into 10epochs, that resulted in the first reconstruction of a geomagnetic secular variation curve(SVC). Even if nowadays the Folgheraiter analytical results have been replaced by moreprecise measurements, a great portion of the development of modern archaeomagnetictechniques originated with Folgheraiter's experiments and intuitions. Many of thoseadvances were improved upon only during the first half of the twentieth century by EmileThellier (1904-1987). Actually, the well-known work by Thellier, resulting in the birthof the Saint Maur archaeomagnetic laboratory at the Institut de Physique du Globe deParis, had as a starting point the theories and suggestions developed by GiuseppeFolgheraiter. Based on the studies by Thellier, the well-known secular variation curvefor France was derived, later to be perfected by Ileana Bucur in 1994.