Abstract

SummaryThe events and thoughts which brought Michael Faraday to the discovery of diamagnetism in the year 1845 are reviewed and commented. The contribution of Bancalari, namely the discovery of diamagnetism in flame and gases made at the University of Genoa in 1847, had a strong impact on the continuation of Faraday's brilliant researches on magnetism in matter. Diamagnetism was carefully studied by him and other authors, while paramagnetism was revealed in solid, liquid, and gaseous substances. A systematic study of the magnetic properties of matter thus had its very beginning.The great number of skilful experiments carried out by Faraday from 1849 to 1851 led him to check in detail, in the case of magnetism, his concept of lines of force. In 1852, with the new phrase ‘physical lines of magnetic force’, Faraday was able to introduce and extensively discuss what may be called today a ‘field theory’ suitable for the description of magnetic action both inside and outside matter.Faraday's suspicious attitude toward the atomic theory prevented him proposing a microscopic explanation of the magnetic properties of matter. The thinking of Ampère and his followers was different; they developed models in order to understand magnetism in matter in terms of molecular currents. Bancalari, under the influence of Avogadro, was a convinced supporter of the atomic theory. Unfortunately, from the scanty documents, it is not possible to infer whether he had in mind any particular model for molecular magnetism.