CAVALLO, TIBERIUS, a distinguished electrician, was born at Naples in 1749, and in the university of that city ho completed his education. In 1771 he was sent to London, in order that he might obtain • correct knowledge of the mode in which mercantile trans action. era conducted in England, but he soon abandoned the pursuits of commerce for those of natural philosophy, and in these he con tinued to be engaged till his death, which took place December 6, 1809. Ile was bused in old St. Pancras churchyard, London.
Cavallo was less distinguished for originality of thought than for his vast industry in the research of the laws of nature by the way of observation and experiment, and for his highly retentive memory; he possessed this faculty to such a degree that, at an ego when ho was unable to comprehend the reasoning employed, he knew by heart all the propositions and demonstrations in the books of Euclid. He had coneihrable skill in music, for which he retained the taste even after his sense of hearing was considerably Impaired. lie was appointed a member of the Academy of Sciences of Naples in 1779, and in the same year be was elected a fellow of the Royal Society of London.
The labours of Cavallo consisted chiefly in the performance of experiments relating to electricity and magnetism, by which he con tributed much to the improvement of those branches of philosophy : he also made researches concerning the composition of the atmoepliero and the characters of minerals. In order to determine the nature of the electricity in the atmosphere ho employed what he called an atmospherical collector:' this was is long rod having at one extremity a small glass tube terminating with a cork from which were suspended two pith balls. The rod being held out as far as possible from an upper window of the house, when the balls diverged by the electricity of the atmosphere, they were drawn In, and the nature of the electric fluid was ascertained by examination. In 1775, while residing near Islington, he made a remarkable experiment with a kith, raised in tho air to the height allowed by 120 yards of string, from which he ascertained that a great quantity of electricity may exist in the atmosphere without producing thunder or lightning. A email cloud passing over the house, he charged some jars with the electricity obtained from it, which lie found to be positive ; by degrees the qusutity diminished till it became insensible, but after a short time - a great dark cloud rising towards the zenith, the fluid, which began again to be manifest, was found to be negative : the electricity con tinuing to increase and the rain falling copiously, he pulled in the kite lest Roma serious accident should happen ; and in doing this, he received many strong shocks in his arms, breast, and legs. He
frequently made experiments of this kind, with kites which were about four feet long and two feet wide ; the string was of common' twine twisted with threads of fine copper-wire.
He invented an instrument called a condenser of electricity,' which consisted of a tin plate between two parts of a wooden frame covered interiorly with gilt paper : the plate was isolated by being supported on glass pillars; and one edge being connected with the body contain ing the electricity, the effect of the condensation was shown, at the opposite edge, by the electrometer. He invented also a `multiplier' of electricity, which consisted of two brass plates insulated by being supported on glass pillars, and of a third plate which conld be insu lated or uninsulated at pleasure: this last being fixed to a lever which turned on a pivot, after receiving electricity from one of the former plates, conveyed it to the other, with which an electrometer was con nected: returning from the second plato to the first it received a fresh supply of electricity, which it conveyed in like manner to the other ; and ao on, till a sufficient quantity was accumulated on the latter.
Among his experiments was one in which were exhibited some remarkable phenomena of the electricity in glass tubes containing mercury. The mercury was boiled in the tube, and the latter being afterwards sealed, on elevating and depressing alternately the ends, electricity was excited by the friction of the mercury : this changed from positive to negative, and the contrary, as the tube was placed in direct and inverted positions.
Cavallo invented also a simple micrometer consisting of a thin and narrow slip of mothor-of-pearl divided into parts each equal to 1-200th of an inch ; this being fixed in the diaphragm of a telescope, at the focus of the eye-glass, served for measuring small angles.
Besides four Bakarian lectures on thermometrical and magnetical phenomena, and several papers on electricity and other subjects, in the 'Philosophical Transactions,' Cavallo published, in London :-1, A Complete Treatise on Electricity,' 8vo, 1777; 2, 'An Essay on the Theory and Practice of Medical Electricity,' 8vo, 1780; 3, 'A Treatise on the Nature and Properties of Air,' Itc., 4to, 1781; 4, 'The History and Practice of ' 8vo, 1785; 5, 'Mineralogical Tablas, 1785; 6, 'A Treatise on Magnetism in Theory and Practice,' 8vo, 1787; 7, 'Description and Use of the Mother-of-Pearl Micrometer,' 8vo, 1793; 8, 'Essay on the Medicinal Properties of Factitious Airs; &c., 8vo, 1798; and 9, Elements of Natural and Experimental Philosophy,' 4 vols. 8vo, 1803.