Page:Encyclopædia Britannica, Ninth Edition, v. 24.djvu/308

Rh 284 V O L T A VOLTA, ALESSANDEO (1745-1827), was born at Como on February 18, 1745. In 1774 he was appointed pro fessor of physics in the gymnasium of Como, and in 1777 he left his native town for the first time to travel through Switzerland, where he formed an intimate friendship with De Saussure. In 1779 a chair of physics was founded in Pavia, and Volta was chosen to occupy it. In 1782 he undertook a journey through France, Germany, Holland, and England, and became acquainted with nearly all the scientific celebrities of that day. In 1791 he received the Copley medal of the Royal Society. In 1801 Napoleon called him to Paris, to show his experiments on contact electricity, and a medal was struck in his honour. He was made a senator of the kingdom of Lombardy. In 1815 the emperor of Austria made him director of the philosophical faculty of Padua. In 1819 he retired, and settled down again in his native town. He died on March 5, 1827. The first published paper of Yolta (De Vi Attractiva Ignis Elcctrici) dates from 1 769 ; it contains no new facts, but deserves our attention as showing us the knowledge with which Volta set cut on his journey of discoveries, and the theoretical speculations which seem to have given him the first impulse to experimental work. Franklin, who was then justly considered the great authority on these matters, had endeavoured to explain electrical phenomena by the mutual repulsion of the particles of an electrical substance and the attraction between that electrical substance and ordinary matter. Volta tried to simplify the theory by assuming an action only -between the electrical substance and matter, and he tells us that he explained his views in a letter to the Abbe Nollet when he was nineteen years old. The way in which he endeavoured to account for the phenomena of attraction and repulsion and the phenomena of the Leyden jar have no interest for us to-day, but that part of his paper in which he showed the application of his theory to the generation of electricity is of historical importance, for in it we can trace the germ of many future discoveries. He imagines all bodies in the natural state to contain electricity in such propor tion that they are in electrical equilibrium. Ho believes that his experimental results obtained by rubbing metals with each other -show this. Hut when bodies are brought into close contact, as, for instance, in friction, adopting the views of Boscovich, according to which attraction and repulsion alternate at small distances, he con siders that the attractions of electricity and matter may alter and a new electrical equilibrium will establish itself. He asks the question whether during the progress of chemical action, such as solution, mixture of fluids, combustion, in which the particles of matter change their position, there is no disturbance of electrical equi librium. He expresses his conviction that this is the case, and explains the experimental difficulties which prevent a proof, but expresses a hope that he will succeed in obtaining signs of electrical action during chemical operations. He shows how atmospheric electricity might bo accounted for in accordance with these views. The principal point of interest in his second paper (Novus ac Simplicissimus Elcctricorum Tentaminum Apparatus) is the attempt to explain electrical insulation by a repulsion between the insulating matter and electricity. The influence of Boscovich in this attempt to explain everything by forces and centres of force is here apparent. Theory thus seems to have given Volta the first impulse to his electrical inquiries; but as he went on with his experimental work the firm establishment of facts took the first place in his mind, and after the first two papers we find hardly anything speculative iu his writings. On June 10, 1775, Volta announced the construction of the electrophorus in a letter to Priestley, asking him, as the historian of electricity, how far the discovery was new. The remainder of the year seems to have been taken up with improvements in the mechanical construction of the apparatus. A letter to De Saussure in 1778 treats of the electrostatic capacity of conductors. Although we now know that Cavendish had treated the same subject in a much more complete way, the researches of Cavendish have only recently been published, and Volta s experiments are a great advance on anything that had been published at the time. The construc tion of the condenser, and its applications to the study of electrical phenomena, were first published in the Philosophical Transactions (1782). By means of the delicate apparatus at his disposal he re turned to the ideas announced in his first paper, and tried to discover signs of electricity during the processes of evaporation and ebulli tion, and during changes of temperature ; after repeated failure he at last believed himself to have succeeded in obtaining electrical effects during the evaporation of water. The first successful experi ments were made in Paris in the presence of Lavoisier and Laplace. We know now that evaporation by itself does not cause a difference in electric potential, and that Volta s effect was due to friction of the vapour generated against the sides of the vessel ; but this has only been established quite recently. The results on electrical effects due to evaporation led Volta to the closer investigation of the phenomena of atmospheric electricity, a subject which seems always to have had a special attraction for him. Between 1788 and 1790 he wrote nine letters on Meteorologia Elcttrica addressed to Lichtenbcrg. The first two letters treat of electrical measurements. For the pith ball electroscope he substi tutes the straw electrometer, in which the angle of divergence of two electrified straws is measured. Different electrometers of various sensitiveness are carefully graduated and compared with each other. Nor is this all : Volta has never as yet received the credit of having constructed the first absolute electrometer, and for having compared his other instruments with it, so that it would be possible now to refer all his measurements to absolute units. His electrometer consisted of a balance, one pane of which was a flat round disk. Below this disk was placed a larger parallel plate, conducted away to earth, and stops were arranged so that the disk could not approach the plate nearer than 2 inches. In the unclectrified state the balance was in a state of equilibrium. When the disk is electrified it is attracted towards the plate but kept at its proper distance by the stops ; weights are then added in the other plate of the balance until the disk is torn away from the stops. The remaining letters addressed to Lichtenberg contain obser vations on atmospheric electricity and on the action of points and flames in discharging electricity. The reader cannot help feeling how very little more we now know about these matters than Volta did. It was probably in 1790 that Galvani first made the observa tions which have rendered him celebrated. He was struck by the muscular contractions of a frog which had recently been killed and skinned, and was lying on a table near an electrical machine, which was accidentally set to work. In order to see whether he could obtain similar contraction from atmospheric electricity, he sus pended the thigh of a frog by means of a hook from an iron railing, and found the contraction whenever the muscle touched the railing. He tried to account for the observation by assuming that the nerves and muscles of the animal body formed a kind of Leyden jar, which was discharged whenever an external circuit brought them into electrical contact. Volta at first agreed to this explanation, but his own experiments soon led him to change his opinion. It is very instructive to read the various letters and essays in which Voltn describes his observations and his reasoning which gradually led him up to the construction of the electrical pile. His whole ex perimental training as well as the speculations of his early youth seemed to force him on in the right path, and in this work, as indeed in his whole career, none of the discoveries seems due to chance. The muscle of the frog soon appeared to him to be nothing but a very delicate electrometer, and lie made use of it as such. The conductors lie divided into two classes. Conductors of the first kind, to which carbon and the metals belong, he showed to become electrified by contact, but in such a way that equilibrium is estab lished in each circuit, so that no current of electricity can be produced by any arrangement containing conductors of this class only. Conductors of the second kind are what we should now call electrolytes. An electric current is produced whenever a circuit is arranged between two conductors of the first kind and one of the second kind. It is impossible here to enter into the history of this now celebrated contact theory, but, although opinions may difi er on the interpretation of some of the experiments, there is not much in Volta s writings on this subject which could be called incorrect even at the present day. Volta s electric pile, was first described in a letter to Sir J. Banks, then president of the Royal Scciety. The letter is dated March 20, 1800, and it was read before the Society on June 26 of the same year. The pile consisted of a number of disks of tin and an equal number of disks of silver or copper. The zinc and tin plates are in contact, and each pair is separated by some porous matter which is kept moist. He describes a number of experimental results obtained with this pile, and finally shows that all the effects produced are the same as those which can be obtained from electrical machines, and that therefore &quot;galvanism &quot; and &quot;electricity&quot; are identical. Volta lived to see the remarkable development of his science at the hands of Sir Humphry Davy, Oersted, and Ampere, but he was no mathematician, and the subject grew beyond his powers. Ho recognized this with that frank honesty which is apparent in all his writings, and during the last twenty-live years of his life he published nothing on electrical subjects. A complete history of Volta s writings ought to take in much which must be omitted here. His investigations on gas analysis, and his very interesting paper on the expansion of gases by heat, deserve, however, to be mentioned. He showed the causes which had led different experimenters to such inconsistent results, and established independently what is now known as the law of Charles. (A. S.*)