Beschreibung:

VOLTA, Alessandro (1745-1847). Autograph letter signed ('Sono tutto vostro A. Volta') to [Canon Francesco Fromond], Como, 14 November 1775, on a bifolium, 4 pages, 4to (tiny tear in lower edge of 1st leaf affecting one word, lacking address leaf).
VOLTA, Alessandro (1745-1847). Autograph letter signed ('Sono tutto vostro A. Volta') to [Canon Francesco Fromond], Como, 14 November 1775, on a bifolium, 4 pages, 4to (tiny tear in lower edge of 1st leaf affecting one word, lacking address leaf). THE INVENTION OF THE ELECTROPHORE: A MILESTONE IN THE HISTORY OF ELECTRICITY. Volta sends a detailed account of his latest invention, which he has already communicated by letter to Don Marsilio [Landriani, physicist in Turin] and Padre [Carlo] Barletti, mildly reproaching Fromond for not replying to an earlier letter. 'Ho dunque tralle mani il grande Elettrofore del diametro di quasi due piedi che ho fatto terminare tosto che ripatriai. L'attività di questo è veramente sorprendente. Basta dire che ottengo non di rado scintille a dieci, dodici, e più diti trasversi: scintille che appajono in vaghissima forma guizzanti emulatrici appunto del telo di Giove. Per averle tali elettrizzo il mastice per eccesso, e presento allo scudo alzato la punta del dito, ovver facendomi ribrezzo, l'anello d'una chiave, da cui ora balza la scintilla lunga come dissi, e guizzante, or una serie di scintillette crepitanti succedonsi, or ne spiccia con leggier sibilo un lunghissimo fiocco'. The electrophore was a essentially a basic reservoir of static electricity which followed on from the discovery by Musschenbroeck in 1745 of the Leyden jar, a concept making possible the preservation of electrical charges by storing them in a jar of water or mercury. In its simplest form the electrophore consisted of two metallic (usually tin) discs coated on one side with wax or resin and placed one above the other, the upper one having a wooden handle. Friction generated an electrical charge sufficient to produce sparks and other phenomena, of the dramatic nature which Volta recounts above. Volta had written in June 1775 to the physicist Count Landriani announcing that he had experimental data which would confirm his theory of electric fluid in equilibrium and of conductors and non-conductors, and to Priestley a few days later of his invention of an 'elettroforo perpetuo'. The present letter gives a detailed account of his modification of the apparatus by using a hemisphere instead of a flat surface, and reports his astonishingly successful results, indicating his plans to overcome certain operational difficulties, and anticipating that he will build a much larger machine, ('un apparevole grande di sette, otto, e piu piedi', as large as a billiard table but round), which will operate on the principle of a thunder-cloud. Part of the letter is devoted to a discussion of the mastic (resin) used in insulation to store the charges. Volta devoted himself to the study of the physical problems of electricity from 1761, and sent his first paper to Padre Beccaria, friar and astronomer in Turin and author of several works on the subject. In 1775 he was appointed, by the progressive Austrian minister, Count Carlo di Firmian, to be Professor of Experimental Physics at the Gymnasium in Como, and in 1778 obtained the Professorship at the University of Pavia. Faraday said of him in his Researches 'It was Volta who removed our doubtful knowledge'. His invention of the electric pile, in 1800, was one of the most important advances in the history of electricity, and the unit of electric pressure, the volt, is named after him. The present letter, one of several written to Fromond in autumn 1775 on the effectiveness of the electrophore in relation to its dimensions and the mastic used in making it, is published in U. Hoepli's edition of the Opere (1918-29, vol. V, pages 117-122), with a postscript (not present and presumably written on an address leaf which has not survived).