(b. Naples, Italy, 25 September 1836; d. Naples, 20 August 1904), physics.
After receiving his secondary education in Naples, Villari studied at the University of Pisa, where he became professor of mathematics and medicine in 1860. Between 1860 and 1871 he lived, successively, in Florence, Berlin, and Florence again, then became professor of experimental physics at the University of Bologna. In 1900 he returned to Naples, where he taught until his death.
Villari’s major interest centered on the effects of electromagnetic forces on material media. His work was not deeply mathematical; he was primarily an experimentalist who used theories qualitatively. His physical outlook was eclectic, combining elements of the Weberean action-at-a-distance school with Faraday’s empirical discoveries regarding electromagnetic induction. To Villari the central element of electromagnetism was the electrical current; and his most original work consisted of an attempt to explain, from an action-at-a-distance standpoint, the peculiar effects of alternating currents on their conductors.
By 1873 Villari and others had noted that metals emit much more heat when carrying alternating currents than when bearing direct currents. Kelvin and Maxwell explained this increased heat by means of the concept of “self-induction” the continuous change in the magnitude and sign of the alternating current is supposed to produce a changing magnetic field and thus to induce an electromotive force in the conductor, a force that acts to oppose the changes in the current. In order to overcome this opposing force, more energy must be expended than if the force were absent; and this excess energy appears as heat.
To Villari, however, the problem was not one of the action of the current, mediated by the field, upon itself. Rather he believed that the current affect the body of the conductor, which in turn reacts upon the current. He thought that all metals are composed of innately magnetic molecules that are acted on by an electric current because currents exert magnetic forces. When a circuit is first closed, the initial effect of the current as it begins to flow is to produce a realignment of the conductor’s magnetic molecules. As the molecules begin to move under the action of the increasing current, they produce a changing magnetic force in the vicinity of the current. According to Faraday’s law of electromagnetic induction, a changing magnetic force induces an electromotive force; as the moleclues align, they therefore engender an electromotive force that opposes the force producing the current. With alternating currents the magnetic molecules will be moving constantly, and energy will be required to overcome the opposing forces induced by their motion; this energy appears as heat.
Villari’s theory did not have wide influence. His experimental results, however, were well-known and extensively utilized. Nonetheless, even his theoretical opinions are important because they illustrate that, at least on the Continent, certain researchers preferred to work outside a Maxwellian context well into the 1880’s. Whereas the self-induction explanation of Kelvin and Maxwell relied on the mediation of a field to produce the effects on the currents, Villari’s explanation assumed a direct action between the currents and the magnetic molecules. Villari’s magnetic molecules are closely related to the electrically polarizable molecules of Mossotti’s dielectrics, and both were action-at-a-distance theories in that they postulated forces acting directly between various kinds of elemental electrical and magnetic fluids.
Villari’s more important works include “Intorno adalcuni fatti singolari di electtro-magnetismo, ed alla ipotesi di Weber sulle elettro-calamite,” in Nuovo cimento, 21-22 (1865-1866), 415–427; “Influenza della magnetizzazione sulla conducibilità elettrica del ferro,” in Rendiconti dell’Istituto lombardo di scienze e lettere, 2nd ser., 1 (1868), 853–862; “Sulle correnti indotte trail ferro ed altri metalli,” in Nuovo cimento, 2nd ser., 1 (1869), 218–242; “Ricerche sulle correnti interrote ed invertite, studiate nei loro effetti termici ed elettro-dinamici,” in Memorie della R. Accademia delle scienze dell’Istituto di Bologna, 3rd ser., 4 (1873), 157–195; and “Sulla diversa tensione delle correnti electtriche indotte fra circuiti totalmente di rame od in parte di ferro,” ibid., 449–467. Villari’s work on currents is referred to in L. Lorenz, “Ueber die Fortpflanzung der Electricität,” in Annalen der Physik und Chemie, n.s., 7, no. 6 (1879), 141–192.
Jed Z. Buchwald