MACEDONIO, a distinguished natural philosopher, born at Parma in the year 1800. Before he was of an age to explain or even to understand his own feelings, he delighted to pass whole nights in contemplation out of doors, wandering in the fields—a habit which gave a very great impulse to his scientific genius. With a decision, as resolute as it was prompt, he did not mistake his vocation, but at once applied himself to his favourite science, in which at an early age he made great progress. Little was known at that time among natural philosophers respecting the radiation of heat; and Melloni set early to work to advance the cause of discovery in that department of science. He had scarcely left school when the chair of natural philosophy was offered him at the university of Parma; and hydrometry being the special branch allotted to him, he taught it from 1824 to 1831. In the progress of his researches into the nature of radiation he found occasion to employ an ingenious instrument termed the thermoscopium, invented by Nobili, a distinguished physicist of that time, for determining slight variations in the temperature of bodies. Nobili himself appreciated the importance of the results obtained by his young friend, and gave an account of them in an article in the Bibliothèque de Genève. In 1831 political events in Romagna and the duchies compelled Melloni to expatriate himself. He found an asylum in France, where he arrived with his thermoscopium. He there became the friend of Arago, the celebrated secretary of the Académie des Sciences, and was subsequently appointed to a professorship in the college of Dôle, in the department of Jura, a situation which his thirst for discovery induced him to resign. He then went to Geneva, where he was welcomed by Pier Prevost and Auguste de la Rive, who placed at his disposal their rich collection of scientific instruments. After six months' assiduous experimenting he succeeded in establishing a number of important facts with regard to the radiation of heat both through solids and liquids. He hastened to Paris to lay his discoveries before the Academy of Sciences, but being received coldly by that body, Melloni resolved to publish the results of his experiments; this led to his being awarded the Rumford medal by the Royal Society of London. After receiving this foreign tribute to his genius, the Institute of France, in the person of Biot, also acknowledged his merits. (See Mémoires de l'Académie des Sciences de Paris, vol. xiv.) The paper submitted to the academy by Melloni is entitled, Descrizione ed Usi di un Apparecchio proprio a Manifestare ed a Misurare i Fenomeni del Calorico Raggiante. Melloni had now secured his place among the most eminent men of Europe; and, through the influence of Arago and Humboldt, he was enabled to return to his native country with the consent of Austria, then the ruling power in Italy. Under these circumstances, the King of Naples, at the suggestion of Arago, did not hesitate to appoint Melloni director of the meteorological observatory, then in course of erection on the slope of Vesuvius. Among the many brilliant results obtained by Melloni in this new sphere, must be MELMOTH mentioned his discovery of heat in the lunar light, which led to the solution of one of the most important problems of modern physical science, viz., the analogy of radiant heat to light. At the meeting of the Italian scientific congress at Naples in 1845, Melloni was elected vice-president of the physical section. He was made a member of the commission to establish lighthouses on the coast of the kingdom, when he published a very able popular account of Fresnel's pharos. The political events of 1848, and the reaction which followed, again interrupted Melloni's scientific pursuits; for although he had taken no part in politics during his residence at Naples, he was in 1849 ejected from his post simply for the liberal opinions he had once professed, and which he still held. He retired to his villa at Portici, near Naples, where, amid bitterness of spirit and disappointment, his love of science never abated. In 1850 he published there the first volume of La Termocroci, or la Coloreazione Calorifica, which he dedicated to Francis Arago and Alexander Humboldt. This compilation, in which he describes his own conclusions, and sketches methodically the progress of science since his first discovery, did not distract his mind from experimental researches. The last years of his life were devoted to the study of electricity, and he communicated many new facts in this branch of science to the Bibliothèque Universelle de Genève. Melloni opposed with great discrimination several ideas of Faraday with regard to the diminution of velocity observed in an electric current passing through submarine or subterranean wires, as compared with an equal current passing through wires suspended in the air. The Englishman had made experiments, from which he endeavoured to deduce a confirmation of his theory of conductability, to the conclusiveness of which, however, the Italian demurred.

He died of cholera at his villa of Portici on the 11th of August 1854. Besides his principal work, La Termocroci, which he left incomplete, or at least unpublished, he contributed numerous papers to the Annales de Chimie et Physique, the Comptes Rendus of the French Academy; the Bibliothèque de Genève; Atti della Reale Academia di Napoli; and the Museo di Scienze e Letteratura, a Neapolitan periodical, in which may be found his discussions and observations on the action of calamine and the electric current, on polarized light, on ponderable bodies, and also his objections to the theory of Faraday. (For further information respecting Melloni's discoveries, see the Sixth Dissertation, chap. vi., sect. 8; also the article HEAT.)