CAVALLO, Tiberius, an electrician and natural philosopher, born at Naples on the 30th March 1749, and son of a physician established in that city.

His father died when he was only eleven years old, but he received a liberal education through the kindness of his friends, and completed his studies at the university of Naples. He was originally destined for commerce, and came to England in 1771, in order to obtain more complete information respecting the various objects of mercantile pursuit. But he soon abandoned his intention of adopting that mode of life, and determined to devote his time almost exclusively to the cultivation of science, and to the literary employments connected with it. The splendid improvements which had been lately made in electricity easily directed his earliest attention to that amusing department of natural philosophy; but his studies were by no means confined to that subject, and the extent of his diversified researches may be understood from an enumeration of his pincipal publications.

1. Extraordinary Electricity of the Atmosphere in October 1775. Phil. Trans. 1776, p. 407. This observation was made at Islington, where the author then resided; and he seems to have been in some danger of becoming, like another Richmann, a martyr to his zeal in pursuit of his favourite science; for he says that he felt a number of severe shocks while he was holding the wire of his kite.

2. An account of some new Electrical Experiments. Phil. Trans. ∖ Τ^Π, p. 48. He here describes two atmospherical electrometers, and an exhausted tube containing some quicksilver, for illustrating the nature of electrical excitation. A paper of Mr Henly, in the same volume, contains [7:6:253]also some communications from Mr Cavallo, and in particular a remark on the opposite electricities which he detected in the bow and strings of his violin.

3. New Electrical Experiments. Phil. Trans. 1777, p. 388. Relating to changes of the colours of pigments, with a description of a pocket electrometer.

4. A complete Treatise on Electricity, 8vo. London, 1777. German by Gehler, 8vo. Leipz. 1785. French by Silvestre, 8vo, Paris, 1785. Ed. 4, 3 vols. 8vo, London, 1795.

This essay contains a clear and familiar account of the principal facts respecting electricity, which had been discovered at the time of its publication, as well as of the best apparatus and of the most interesting experiments. The first part relates to the general laws of the science; the second to the hypothetical theories by which different authors have attempted to explain them, but without any mention of the calculations of Alpinus and Cavendish; the third part gives an account of the practical arrangement of electrical apparatus, and the fourth of some original experiments and instruments; the fifth part in the later editions is a republication of the author’s Essay on Medical Electricity. To the fourth edition a third volume is added, containing an account of the recent discoveries respecting animal electricity; of the author’s multiplier for detecting the presence of small quantities of electricity, by the repeated operation of two condensers connected together; and of some original and very important experiments relating principally to the effect of the contact of different metals with each other, and exhibiting an imperfect outline of those properties, which have since furnished Volta and Davy with their ingenious explanations of the phenomena of the electrochemical battery.

Mr Cavallo has inadvertently attributed to Nollet the honour of having first entertained the opinion of the electrical nature of thunder and lightning; and the German translator has thought it necessary to vindicate the scientific character of his own country, by laying claim to this conjecture on behalf of Winkler; but Mr Silvestre has remarked, with a laudable impartiality, that both Germany and France must on this occasion give way to England, since the first suggestion of the identity is found in a paper of Stephen Gray, published in the Philosophical Transactions about 1735.

5. An account of some new Experiments in Electricity. Phil. Trans. 1780, p. 15. Consisting of remarks on Professor Lichenberg’s discovery of the peculiarity of the figures exhibited by strewing powders on the cake of the electrophorus; with an account of two improved electrometers.

6. Τherrnometrical Experiments and Observations. Phil. Trans. 1780, p. 585. This was a Bakerian lecture, delivered by appointment of the president and council of the Royal Society, an appointment which entitles the lecturer to a small fee, left by the will of Mr Henry Baker, but which is commonly considered as rather complimentary than lucrative. These experiments relate to the effect produced by colouring the bulb of a thermometer exposed to the sun’s rays, and to the intensity of heat at different distances from its source. The most refrangible colours appeared to absorb the most heat; and it was observed that even the day-light, without sunshine, occasioned a perceptible difference in the indications of the different thermometers.

7. An Essay on Medical Electricity, 8vo, London, 1780. It is seldom that persons not medical have been sufficiently incredulous in their opinions respecting the operations of remedies; and the whole of the expectation held out in this work has certainly not been fulfilled by later experience; but, as a candid and distinct relation of cases, it may still have its value.

8. Account of a Luminous Appearance. Phil. Trans. 1781, p. 329. One of the permanent arches since found to be connected with the aurora borealis. It was so bright that the stars could not be seen through it, and lasted about an hour.

9. Thermometrical Experiments. Phil. Trans. 1781, p. 509. A Bakerian lecture, relating to the evaporation of cther, to the expansion of mercury, and to a thermometrical barometer; that is, a very delicate thermometer for ascertaining the temperature of boiling water at different heights above the level of the sea, according to the idea then suggested by Sir George Shuckburgh, and very lately resumed by other natural philosophers. Mr Cavallo observes that the instrument has the advantage of being very portable; but that unless the quantity of water be considerable, its boiling temperature will be somewhat unsteady.

10. A Treatise on the Air, and other Permanently Elastic Fluids, 4to, Lond. 1781. This elaborate work commences with the principles of chemistry and of hydrostatics, and proceeds to relate all the known properties of the different kinds of elastic fluids, many of which had been very lately discovered. These are followed by an account of some original experiments, for example, on the gas produced by the deflagration of gunpowder, which is found to be chiefly nitrogen and carbonic acid, without any nitric oxide; on the explosion of hydrogen mixed with atmospheric air, and on the evolution of gas from plants, respecting which the author finds some reason to differ from the opinions of Dr Ingenhurz. Considering that Mr Cavendish had not then discovered the composition of the nitric acid, it must be allowed that the experiments on gunpowder may justly be deemed an important step in the progress of chemical science.

11. Description of an Improved Air-Pump. Phil. Trans. 1783, p. 435. The improvement was made by Haas and Hurter, and consisted in a mode of opening the valve of oiled silk mechanically, when the elasticity of the air became too weak to raise it. The rarefaction obtained went to about the thousandth of an atmosphere. In this state the air transmitted electricity, with a light equably diffused; and the balls of the electrometer exhibited no divergence. Some later improvements arc said to have carried the rarefaction to κπ⅛u∙

12. Description of a Meteor. Phil. Trans. 1784, p. 108. This observation was made at Windsor, and is highly valuable, from the circumstance of a noise like thunder having been heard, about ten minutes after the explosion of the meteor was seen; hence the author concludes that its direct distance was 130 miles, and its height 56-i-.

13. The History and Practice of Aerostation, 8vo, Lond. A work of temporary rather than of permanent interest; but which it was the more natural for Mr Cavallo to undertake, as he was one of the first who had made experiments on the means of employing hydrogen for raising bodies into the air by its levity.

14. Mineralogical Tables, f. Explanation, 8vo, Lond. 1785; containing a comparison of the different systems of mineralogical arrangement then most generally adopted, but at present almost wholly superseded by later methods.

15. 16. Magnetical Experiments and Observations. Phil. Trans. 1786, p. 62; 1787, p. 6. Two Bakcrian lectures. The former relates chiefly to the magnetism of brass, and of some other metals, generally rendered discoverable by hammering them. In the latter the same subject is continued; and it is shown that the same powers may be detected in the metals in question without hammering them, if they are placed on a very clean and wide surface of quicksilver. The limit at which red hot iron begins to be attracted by a magnet is found to be the heat at which it [7:6:254]ceases to be visible in the day-light. A considerable change is observed in the magnetic powers of iron during its solution in acids; and the author endeavours to apply these experiments to the explanation of the variation of terrestrial magnetism, as derived from the effects of heat, and from internal changes in the constitution of the earth. Mr Bennet has endeavoured to explain the phenomena observed by Mr Cavallo, from the accidental operation of foreign causes; but he has not been perfectly successful in the attempt.

17. A Treatise on Magnetism in Theory and Practice, 8vo, Lond. 1787, ed. 3, 1800. The arrangement resembles that of the Treatise on Electricity. Under the head of Theory the name of Alpinus is mentioned with due respect. The original experiments are chiefly reprinted from the Philosophical Transactions. There is also a description of an improved mode of suspension for a magnetic needle; and there are several letters from Dr Lorimer on the terrestrial variation.

18. Of the Methods of manifesting the presence of small quantities of Electricity. Phil. Trans. 1788, p. 1. In this Bakerian lecture, Mr Cavallo proposes an improvement on Volta’s condenser, and makes some remarks on Mr Bennet’s doubler, which he thinks objectionable on account of the impossibility to deprive the plate of a small quantity of electricity adhering to it. His own instrument has the advantage of avoiding the friction to which the condensers and doublers in their original form were liable.

19. Of the Temperament of Musical Intervals. Phil. Trans. 1788, p. 238. The author’s particular object is to calculate the exact scale for the division of a monochord, according to the system of a perfectly equal temperament; but he very candidly remarks, that, “for playing solos,” the usual temperament is the best, “giving the greatest effect to those concords which occur most frequently ;” and he says, that when a harpsichord was tuned according to the scale laid down on this monochord, the harmony was perfectly equal throughout, and the effect “the same as if one played in the key of E natural on a harpsichord tuned in the usual manner.”

20. Description of a new electrical Instrument, capable of collecting together a diffused quantity of Electricity. Phil. Trans. 1788, p. 255. This collector consists of a fixed plate of tin, situated between two movable ones; it is said to be more certain in its operation than the condenser, the results of which are liable to considerable irregularities from various accidents, and to be more free from the inconvenience of permanent electricity than the doubler.

21. Description of a Micrometer. Phil. Trans. 1791, p. 283. Description and use of the Mother of Pearl Micrometer, 8vo, Lond. 1793. A thin slip of mother of pearl with a fine scale engraved on it, placed in the focus of the eye-piece of a telescope. Its principal use is for ascertaining the distance of an object of known dimensions by its apparent magnitude thus measured; for instance, to enable one to judge of the distance of a body of troops in military operations. The mother of pearl is found to be more convenient than glass for receiving the divisions, and to be sufficiently transparent for transmitting the images of the respective objects.

22. On the Multiplier of Electricity. Nicholson’s Journal, i. p. 394, 1797. In this letter Mr Cavallo attempts to show the advantage of his instrument over doublers of all kinds. Mr Nicholson, in a very respectful answer, expresses his doubts whether the objections to the doubler do not arise from its extreme sensibility only, as demonstrating the existence of an electricity too weak to affect the other instruments compared with it. Mr Cavallo had however remarked, that the inconvenience partly arose from the greater intensity of the charge committed to the plate of the doubler during the operation, which required a longer time for the restoration of the natural equilibrium.

23. An Essay on the Medicinal Properties of Factitious Airs, with an Appendix on the Nature of the Blood. 8vo, London, 1798. The modern improvements in pneumatic chemistry have been still less productive of advantage to practical medicine than the discovery of the powers of electricity, and this work can scarcely be considered as having conferred any material benefit on the public. The observations on the blood are chiefly the result of a minute and careful microscopical examination of its particles, but the author was not particularly happy in the light which he employed for viewing them.

24. Elements of Natural or Experimental Philosophy, 4 vols. 8vo, Lond. 1803. This work, the last and most valuable of the author’s publications, will long serve as a useful manual of the most important parts of the mechanical and physical sciences. The first volume is devoted to mathematical and practical mechanics, beginning with matter and motion, and proceeding to simple machines. The second relates, first, to fluids, to the principles of hydrostatics, cohesion, hydraulics, pneumatics, sound, and music; and, secondly, to the most important parts of chemistry. In the third volume we find the doctrine of heat, optics, electricity, and magnetism; and the fourth, besides astronomy and the use of the globes, contains a compendium of the history of aerostation; an account of meteors, including the recent discoveries respecting aeroliths; and a collection of useful tables.

25. Mr Cavallo was also an occasional contributor to several periodical publications, and his critical articles were not in every instance anonymous. He was made a member of the Royal Academy of Naples in 1779, and a fellow of the Royal Society of London in the month of December of the same year.

It is impossible to hesitate in attributing to Mr Cavallo the possession of very considerable powers of mind; but these powers seem to have been of a different nature from those which have distinguished some other individuals, remarkable for the faculty of acute reasoning and brilliant invention, and apparently born to succeed in the highest flights of genius. Mr Cavallo’s talents appear to have had more of the imitative character, and to have been rather calculated for the attainment of excellence in the fine arts than in science; but his memory was uncommonly retentive, and his industry seems to have been indefatigable. He used to relate, that when he was first compelled to study Euclid, he felt himself utterly incapable of comprehending the train of argumentation, and he was obliged to get the whole work by heart, both propositions and demonstrations, in order to impress the conclusions strongly on his mind. This expedient answered his purpose very well, as long as the impression lasted; but after some years he had forgotten his task, and he was obliged to go through the whole again in the same manner, still finding it easier to commit the eight entire books, with all the unmeaning letters of reference, to the care of his ever-faithful memory, than to acquire the spirit of the mode of reasoning, and to anticipate the steps of the demonstration; although, after having performed this second labour, he felt himself sufficiently master of the subject. It may be observed that he possessed considerable skill in music; and music was called by the ancients an imitative art, a description which may indeed be somewhat objectionable with regard to the province of the original composer, who creates something altogether unlike what had ever before existed, but which may not improperly be applied to the occupation of a performer; indeed Mr Cavallo, even when his hearing was impaired, still retained[7:6:255] a very correct taste in the execution of vocal music. He possessed also his country’s aptitude for the painter’s art; and he was particularly happy in cutting out striking likenesses of his acquaintances in paper. The principal object of his life was to collect and arrange the labours of others; and he was so much in the habit of collecting, that he had for many years made it his amusement to collect specimens of the handwriting of eminent persons, which he had extended to an immense number of individuals of different ages and countries. But he was by no means incapable of copying from the great book of nature; and he made, in the course of his various researches, a number of original experiments, well calculated to illus-strate particular questions relating to the sciences which lie cultivated. In the latter part of his life he had discontinued his attendance at the meetings of the Royal Society, as well as his contributions to the Transactions ; but he was in the habit of frequenting some other literary conversations, at which he constantly met some of his oldest and kindest friends. A short time before his last illness, he was engaged in some experiments on Mr Deluc’s perpetual pile of paper, and on the electricity of different specimens of crystals; but he does not appear to have obtained any new results from these investigations. He died at his residence in Wells Street, on the 26th of December 1809, and was buried in St Paneras churchyard, near the tomb of General Paoli, with whom he had long been on terms of the greatest intimacy. (Literary Memoirs of īΛving Authors ; Dance’s Collection of Portraits ; Gentlemans Magazine, 1809; Supplement to the Monthly Magazine, 1810, p. 86; Aikin’s General Biography, vol. x.; Chalmers’ Biographical Dictionary, vol. vii.) (l. l.)