Volta made numerous experiments in sup port of his theory and ultimately developed the pile or battery (see VOLTAIC PILE), which was the precursor of all subsequent chemical bat teries, and possessed the distinguishing merit of being the first means by which a prolonged continuous current of electricity was obtainable.
Volta communicated a description of his pile to the Royal Society of London and shortly thereafter Nicholson and Cavendish (1780) produced the decomposition of water by means of the electric current, using Volta's pile as the source of electromotive force. Davy in 1806, employing a voltaic pile of approximately 250 cells, or couples, decomposed potash and soda, showing that these substances were respectively the oxides of potassium and sodium, which metals previously had been unknown. These experiments were the beginning of electro chemistry (q.v.), the investigation of which Faraday took up, and concerning which in 1833 he announced his important law of electro chemical equivalents, viz.: same quan tity of electricity — that is, the same electric current — decomposes chemically equivalent quantities of all the bodies which it traverses; hence the weights of elements separated in these electrolytes are to each other as their chemical equivalents.° Employing a battery of 2,000 elements of a voltaic pile Humphrey Davy in 1809 gave the first public demonstra tion of the electric arc light (q. v.), using for the purpose charcoal enclosed in a vacuum.
Somewhat singular to note, it was not until many years after the discovery of the voltaic pile that the sameness of annual and frictional electricity with voltaic electricity was clearly recognized and demonstrated. Thus as late as January 1833 we find Faraday writing ((Philo sophical Transactions,' 1833) in a paper on the electricity of the torpedo. °After an examina tion of the experiments of Walsh, Ingenhousz, Cavendish, Sir H. Davy, and Dr. Davy, no doubt remains on my mind as to the identity of the electricity of the torpedo with common (fric tional) and voltaic electricity; and I presume that so little will remain on the mind of others as to justify my refraining from entering at length into the philosophical proof of that identity. The doubts raised by Sir H. Davy have been removed by his brother, Dr. Davy; the results of the latter being the reverse of those of the former. . . . The general con clusion which must, I think, be drawn from this collection of facts (a table showing the similar ity ,of properties of the diversely named elec triaties) is, that electricity, whatever may be its source, is identical in its nature.) It is proper to state, however, that prior to Faraday's time the similarity of electricity de rived from different sources was more than suspected. Thus, William Hyde Wollaston, b.
1766; d. 1828 (another noted and careful experi menter in electricity and the discoverer of pal ladium and rhodium), wrote in 1801 (Philo sophical Magazine, Vol. III, p. 211) : °This similarity in the means by which both electric ity and galvanism (voltaic electricity) appear to be excited in addition to the resemblance that has been traced between their effects shows that they are both essentially the same and confirm an opinion that has already been advanced by others, that all the differences discoverable in the effects of the latter may be owing to its being less intense, but produced in much larger quan tity." In the same paper Wollaston describes certain experiments in which he uses very fine wire in a solution of sulphate of copper through which he passed electric currents from an elec tric machine. This is interesting in connection with the later day use of almost similarly ar ranged fine wires in electrolytic receivers in wireless, or radio-telegraphy.
In the first half of the 19th century many very important additions were made to the world's knowledge concerning electricity and magnetism. For example, in 1819 Hans Chris tian Oersted of Copenhagen discovered the de flecting effect of an electric current traversing a wire upon a suspended magnetic needle. This discovery gave a clue to the subsequently proved intimate relationship between electricity and magnetism which was promptly followed up by Ampere who shortly thereafter (1821) an nounced his celebrated theory of electro dynamics, relating to the force that one current exerts upon another, by its electromagnetic effects, namely: (1) parallel portions of a circuit attract one another if the currents in them are flowing in the same direction, and re pel one another if the currents flow in the oppo site direction. (2) Two portions of circuits crossing one another obliquely attract one an other if both the currents flow either towards or from the point of crossing, and repel one an other if one flows to and the other from that point. (3) When an element of a circuit exerts a force on another element of a circuit, that force always tends to urge the latter in a direc tion at right angles to its own direction." Professor Seebeck, of Berlin, in 1821 discov ered that when heat is applied to the junction of two metals that had been soldered together an electric current is set up. This is termed Thermo-Electricity. (See Seebeck's device consists of a strip of copper bent at each end and soldered to a plate of bis muth. A magnetic needle is placed parallel with the copper strip. When the heat of a lamp is applied to the junction of the copper and bis muth an electric current is set up which deflects the needle.