Abstract
A new method has been tested on Etna historic lavas for determining the geomagnetic field intensity ( F) using the thermoremanent magnetization of volcanic rocks. The procedure involves a number of very short duration heatings above the Curie point, to produce successive laboratory TRM. Thus, it is possible to check the variations in the TRM-acquiring capacity of the samples with the time of heating ( t). The curve J = f( t) is then extrapolated towards t = 0, leading to a virtual value of TRM without any laboratory heating, i.e., without the changes that currently occur when the lavas are heated to produce the TRM. Using such virtual values of TRM, satisfactory results of F had been derived from the majority of the samples studied. These results are consistent with Thellier's archeomagnetic data: they show a nearly constant intensity of the geomagnetic field during the last three centuries and, further back into the past, a significant increase of this.
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