ELECTRICITY 



different metals when immersed in 

 a solution of a salt or acid remain 

 at slightly different potentials even 

 when connected with a conducting 

 wire, and so on any theory of the 

 material nature of electricity, there 

 must be a flow of electricity along 

 the wire. Further, that by connect- 

 ing any number of such " voltaic 

 cells" in series there is theoreti- 

 cally no limit to the difference of 

 potential which can be established 

 between the terminal plates of the 

 battery (excepting, of course, a 

 breakdown in the insulating power 

 of the air). During the early years 

 of the century various batteries of 

 a more constant strength were de- 

 vised by Daniell, Grove, Smee, and 

 others, and employed in the study 

 of electro-chemical decomposition 

 of solutions, the earliest attempts 

 in this direction being made by 

 Carlisle, Nicholson, and Davy in 

 England, and Hitter in Germany. 

 These researches were continued 

 later by Faraday with signal suc- 

 cess, and in 1835 modern physical 

 and electro-chemistry may be said 

 to have come into being with the 

 enunciation of Faraday's well- 

 known laws of electrolysis. 

 Science of Electro-Magnetism 



In another direction Volta's work 

 was to lead to still greater results. 

 In 1819 Oersted of Copenhagen dis- 

 covered the existence of a " cir- 

 cuital " magnetic field round a wire 

 joining the terminal plates of a 

 battery. The science of electro- 

 magnetism originated in that ex- 

 periment. Within a few years 

 Ampere had extended Oersted's ex- 

 perimental work and had published 

 a mathematical theory of it, after- 

 wards amplified by Weber. Gal- 

 vanometers of various types were 

 invented by Nobili, Pouillet, Thom- 

 son, and D' Arsonval. But no inves- 

 tigations rank higher than those of 

 G. S. Ohm, who between 1825 and 

 1830 published the results of his 

 work on the connexion between 

 current strength in a conducting 

 wire and electromotive force. 



It is a rather deplorable fact 

 that the very thorough and com- 

 plete experimental work which 

 Ohm carried out in support of his 

 famous law is absent from nearly 

 all current text-books. In fact, 

 even in his own day, many physi- 

 cists were entirely ignorant of his 

 experiments and believed that he 

 had only given a theoretic deduction 

 of the law. The introduction of the 

 concept of " resistance " into elec- 

 trical science produced consider- 

 able reactions both in theory and 

 experiment, and by 1843 Wheat- 

 stone, then holding the chair ot 

 physics at King's College, London, 

 had perfected his well-known 

 method for determining resistance. 



2844 



Michael Faraday's work on elec- 

 trolysis has already been men- 

 tioned. But his work on electro- 

 magnetism was destined to play a 

 more revolutionary part in science. 

 By 1831 he had discovered the exis- 

 tence of electromagnetic induction, 

 i.e. the creation of electric currents 

 in a conductor by the variation of a 

 surrounding magnetic field. Later, 

 continuing some investigations of 

 Jenkin, he discovered the phenome- 

 non of self-induction. It should be 

 stated that similar results were ob- 

 tained independently and almost 

 simultaneously by Joseph Henry 

 at Albany, New York. Modern 

 dynamo-electric machinery origin- 

 ated in these famous experiments. 

 Faraday and Clark Maxwell 



In another direction Faraday 

 revolutionised electric theory. He 

 destroyed the old " action at a 

 distance " view of electric force by 

 his discovery of the effect of the 

 surrounding medium on the force 

 between two charged bodies the 

 " specific inductive capacity " of 

 the medium, as it is called. This 

 discovery led Faraday to postu- 

 late transmission of electric force 

 through the " polarised " particles 

 of the medium, a view which was 

 eagerly accepted by J. Clark 

 Maxwell and developed by him 

 with great mathematical power in 

 his famous work on the subject. In 

 Maxwell's hands the theory pre- 

 dicted the transmission of electric 

 waves through space, a result 

 beautifully confirmed -in 1888 by 

 Hertz, which has had such mar- 

 vellous fruition in wireless tele- 

 graphy and telephony. 



Space only permits us to men- 

 tion that the work of the twentieth 

 century has had its own distinctive 

 impress. Beginning with the experi- 

 ments of J. J. Thomson on electric 

 discharge in vacuum tubes and of 

 Curie, Rutherford, and Soddy on 

 radioactive materials, it is unlock- 

 ing the secret of the atom and find- 

 ing confirmation of Du Fay's old 

 notion of the two " fluids," in the 

 " electron " and the " positive 

 nucleus," the planet and sun of the 

 " solar system " which is accepted 

 by all physicists nowadays as a 

 working model of atomic structure. 



James Rice 



ELECTKICITY IN MEDICINE. It 

 is not surprising, having regard to 

 some of its remarkable manifes- 

 tations, that the idea should have 

 presented itself to many minds 

 that electricity is a " vital " force. 

 It has been long recognized that it 

 is a force that kills ; and the con- 

 peption that it should be able to 

 cure, more or less, the physical ail- 

 ments of man is not unnatural. Un- 

 fortunately a good deal of charlat- 

 anism has been associated with the 



ELECTRICITY 



idea of the curative powers of elec- 

 tricity, not only in Great Britain, 

 but perhaps still more on the con- 

 tinent of Europe and in America. 

 The so-called electric or magnetic 

 " belts " in connexion with which 

 the public is frequently informed 

 that " electricity is life," may be 

 dismissed quite briefly. As a 

 matter of fact magnetism alone has 

 no physiological action whatever. 

 Any curative effects which such ap- 

 pliances may appear to produce are 



Electricity in medicine. Patient with 

 hand and foot in electrical bath under- 

 going treatment for heart disease 



due to the warmth which they com- 

 municate to the body of a patient 

 by their substance only, and to the 

 faith which they inspire in his mind, 

 and not at all to any electrical power 

 which they possess. 



For the first demonstration of the 

 physiological effects of electricity 

 we have to go back to 1678, when 

 Swammerdam showed to the Grand 

 Duke of Tuscany that a piece of the 

 muscle of a frog's leg hanging by a 

 thread of nerve bound with silver 

 wire would instantly contract if 

 both nerve and wire were simul- 

 taneously touched by a piece of 

 copper. Galvani and Volta, not 

 knowing of Swammerdam's demon- 

 stration, made their classical ex- 

 periments on dead frogs and their 

 legs more than a century later, and 

 first excited general scientific in- 

 terest in the physiological effects 

 of electricity. Since then many 

 experiments" have been made on 

 newly killed animals, always with 

 the result that muscular move- 

 ments were produced. 



In practice electricity is used hi 

 the three forms, static, galvanic, 

 or continuous, and alternating, or 

 what is sometimes termed faradic. 

 For the production of the first the 

 Wimshurst influence machine may 

 be used. This form is employed to 



