(b. Naples, Italy, 30 March 1749; d. London, England, 21 Decernber 1809),
Cavallo, the son of a Neapolitan physician, did his scientific work in England, where he settled in 1771 intending to acquire some experience in business. He apparently put aside his plans on becoming acquainted with some amateur English physicists, particularly William Henley, who introduced him to experimental philosophy and encouraged him in its pursuit. He became a fellow of the Royal Society in 1779.
Cavallo’s first studies (1775–1776) concerned mospheric electricity, which he explored with Franklin kites and with improved detectors of his own invention, fashioned after Canton’s pith-bail electroscope. Although little came of his investigations (beyond the intelligence that rain often carries a negative charge), they required a course of self-instruction that culminated in Cavallo’s most important work. A Complete Treatise on Electricity in Theory and Practice (1771). A second edition, with revisions, appeared in 1782 and a third, in three volumes, between 1786 and 1795. An excellent compendium, the Treatise served the needs of both the neophyte and the initiate, who found in its appendixes valuable details about medical electricity; about Beccaria’s obscure theories; and about Cavallo’s forte, the design and operation of electrostatic instruments.
With the publication of the Complete Treatise Cavallo switched his attention to the physics of the atmosphere and to the constitution of “permanently elastic fluids.” Again his strengths appeared in instrumentation—an improved air pump and a modified eudiometer—and in smoothing the way for others. This time his course of self-instruction, A Treatise on the Nature and Properties of Air and Other Permanently Elastic Fluids (1781), was a judicious examination of contemporary work, particularly Priestley’s, presented from a nondogmatic phlogistic point of view. He always retained a lively interest in pneumatic physics and chemistry, whose applications to ballooning and to medicine became subjects of two later books.
Cavallo also gave some attention to magnetism, on which he delivered a Bakerian lecture to the Royal Society in 1786 and published a treatise the following year; and he had a sustained interest in music— he was an amateur violinist—which led him to an investigation of the temperament of fretted instruments (1788). The inevitable text on the physics of music appeared in Cavallo’s last, most ambitious, and least successful exposition: his wordy, overly elementary Elements of Natural Philosophy (1803).
I. Original Works. Cavallo’s most important works are “Some New Electrical Experiments”, in Philosophical Transactions of the Royal Society, 67:1 (1777), 48–55; “New Electrical Experiments and Observations, With an Improvement of Mr. Canton’s Electrometer”, ibid., 67:2 (1777), 388–400; A Complete Treatise on Electricity in Theory and Practice With Original Experiments (London, 1777; 2nd ed., rev., 1782; 3rd ed., 3 vols., 1786–1795); An Essay on the Theory and Practice of Medical Electricity (London, 1780; 2nd ed., 1781); A Treatise on the Nature and Properties of Air and Other Permanently Elastic Fluids…. (London, 1781); “Description of art Air Pump”, in Philosophical Transactions of the Royal Society, 73 (1783). 435–452; The History and Practice of Aerostation [ballooning] (London, 1785); A Treatise on Magnetism in Theory and Practice (London, 1787; 2nd ed., 1800); “Of the Methods of Manifesting the Presence, and Ascertaining the Quality, of Small Quantities of Natural or Artificial Electricity”, in Philosophical Transactions of the Royal Society, 78 (1788), 1– 22, the Bakerian lecture: “Description of a New Electrical Instrument Capable of Collecting Together a Diffused or Little Condensed Quantity of Electricity”, ibid., 255– 260; “Of the Temperament of Those Musical Instruments, in Which the Tones, Keys or Frets, Are Fixed…”, ibid., 238–254; An Essay on the Medical Properties of Factitious Air… (London, 1798); and Elements of Satural Philosophy (London, 1803).
No satisfactory bibliography for Cavallo exists; Poggendorff omits several contributions even to the Philosophical Transactions. There is a collection of Cavallo’s correspondence (115 letters, 1782–1809) at the British Museum (Add MSS 22,897 and 22,898).
II. Secondary Literature. Biographical information about Cavallo must be culled from his correspondence at the British Museum; obiter dicta in his papers; the Canton MSS II, 103, 107–108, at the Royal Society; Dictionary of National Biography, III, 1246–1247; and Nouvelle biographie générale, IX, 285. For his most significant scientific work see W. C. Walker, “The Detection and Estimation of Electric Charges in the Eighteenth Century”, in Annals of Science, 1 (1936), 66–100. For his contributions to chemistry and animal electricity see, respectively, J. R. Partington, A History of Chemistry, III (London, 1962). 89. 300, 324; and P. C. Ritterbush, Overtures to Biology. The Speculations of Eighteenth-Century Naturalists (New Haven-London,1964), passim.
John L. Heilbron