April T, 1881] 



NATURE 



537 



finding out what was this electrotonic state. He dis- 

 covered at first, in 1838, the dielectric polarisation of 

 electric insulators, subject to electric forces. Such bodies 

 show, under the- influence of electric forces, phenomena 

 perfectly analogous to those exhibited by soft iron under 

 the influence of the magnetic force. Eleven years later, 

 in 1849, he was able to demonstrate that all ponderable 

 matter is magnetised under the influence of sufficiently 

 intense magnetic force, and at the same time he disco- 

 vered the phenomena of diamagnetism, which indicated 

 that even space, devoid of all ponderable matter, is 

 magnetisable ; and now with quite a wonderful sagacity 

 and intellectual precision Faraday performed in his brain 

 the work of a great mathematician without using a single 

 mathematical formula. He saw with his mind's eye that 

 by these systems of tensions and pressures produced by 

 the dielectric and magnetic polarisation of space which 

 surrounds electrified bodies, magnets or wires conducting 

 electric currents, all the phenomena of electro-static, 

 magnetic, electro-magnetic attraction, repulsion, and 

 induction could be e.xplained, without recurring at all to 

 forces acting directly at a distance. This was the part 

 of his path where so few could follow him ; perhaps a 

 Clerk Maxwell, a second man of the same power and 

 independence of intellect, was necessary to reconstruct 

 in the normal methods of science the great building, the 

 plan of which Faraday had conceived in his mind and 

 attempted to make visible to his contemporaries. 



Nevertheless the adherents of direct action at a distance 

 have not yet ceased to search for solutions of the electro- 

 magnetic problem. The present development of science, 

 however, shows, as I think, a state of things very favour- 

 able to the hope that Faraday's fundamental conceptions 

 may in the immediate future receive general assent. His 

 theory, indeed, is the only existing one which is at the 

 same time in perfect harmony with the facts observed, 

 and which at least does not lead into any contradiction 

 against the general axioms of dynamics. 



It is not at all necessary to accept any definite opinion 

 about the ultimate nature of the agent which we call 

 electricity. 



Faraday himself avoided as much as he could giving 

 any affirmative assertion regarding this problem, although 

 he did not conceal his disinclination to believe in the 

 existence of two opposite electric fluids. 



For our own discussion of the electro-chemical pheno- 

 mena, to which we shall turn now, I beg permission to 

 use the language of the old dualistic theory, because 

 we shall have to speak principally on relations of 

 quantity. 



I now turn to the second fundamental problem aimed at 

 by Faraday,- the connection between electric and chemical 

 force. Already, before Faraday went to work, an elaborate 

 electro-chemical theory had been established by the re- 

 nowned Swedish chemist Berzelius, which formed the 

 connecting-link of the great work of his life, the systema- 

 tisation of the chemical knowledge of his time. His 

 starting point was the series into which Volta had 

 arranged the metals according to the electric tension 

 which they exhibit after contact with each other. A 

 fundamental point which Faraday's experiment contra- 

 dicted was the supposition that the quantity of electricity 

 collected in each atom was dependent on their mutual 

 electro-chemical differences, which he considered as the 

 cause of their apparently greater chemical affinity. But 

 although the fundamental conceptions of Berzelius' theory 

 have been forsaken, chemists have not ceased to speak 

 of positive and negative constituents of a compound body. 

 Nobody can overlook that such a contrast of qualities, as 

 v/as expressed in Berzelius' theory, really exists, well- 

 developed at the extremities, less evident in the middle 

 terms of the series, playing an important part in all 

 chemical actions, although often subordinated to other 

 influences. 



When Faraday began to study the phenomena of de- 

 composition by the galvanic current, which of course 

 were considered by Berzelius as one of the firmest sup- 

 ports of his theory, he put a very simple question, the 

 first question indeed which every chemist speculating 

 about electrolysis ought to have answered. He asked. 

 What is the quantity of electrolytic decomposition if the 

 same quantity of electricity is sent through several elec- 

 trolytic cells ? By this investigation he discovered that 

 most important law, generally known under his name, but 

 called by him the law of definite electrolytic action. 



Faraday concluded from his experiments that a definite 

 quantity of electricity cannot pass a voltametric cell 

 containing acidulated water between electrodes of plati- 

 num without setting free at the negative electrode a 

 corresponding definite amount of hydrogen, and at the 

 positive electrode the equivalent quantity of oxygen, one 

 atom of oxygen for every pair of atoms of hydrogen. If 

 instead of hydrogen any other element capable of substi- 

 tuting hydrogen is separated from the electrolyte, this is 

 done also in a quantity exactly equivalent to the quantity 

 of hydrogen which would have been evolved by the same 

 electric current. 



Since that time our experimental methods and our 

 knowledge of the laws of electrical phenomena have 

 made enormous progress, and a great many obstacles 

 have now been removed which entangled every one of 

 Faraday's steps and obliged him to fight with the con- 

 fused ideas and ill-applied theoretical conceptions of 

 some of his contemporaries. We need not hesitate to 

 say that the more experimental methods were refined, 

 the more the exactness and generality of Faraday's law 

 was confirmed. 



In the beginning Berzelius and the adherents of Volta's 

 original theory of galvanism, based on the eftects of 

 metallic contact, raised many objections against Faraday's 

 law. By the combination of Nobih's astatic pairs of 

 magnetic needles with Schweigger's multiplicator, a coil 

 of copper wire with numerous circumvolutions, galvano- 

 meters became so delicate that the electro-chemical 

 equivalent of the smaller currents they indicated was 

 imperceptible for all chemical methods. With the 

 newest galvanometers you can very well observe currents 

 which would want to last a century before decomposing 

 one milligram of water, the smallest quantity which is 

 usuallv weighed on chemical balances. You see that if 

 such a current lasts only some seconds or some minutes, 

 there is not the slightest hope to discover its products of 

 decomposition by chemical analysis. And even if it 

 should last a long time the feeble quantities of hydrogen 

 collected at the negative electrode can vanish, becau.se 

 they combine with the traces of atmospheric oxygen 

 absorbed by the liquid. Under such conditions a feeble 

 current may continue as long as you like without pro- 

 ducing any visible trace of electrolysis, even not of 

 galvanic polarisation, the appearance of which can be 

 used as an indication of previous electrolysis. Galvanic 

 polarisation, as you know, is an altered state of the 

 metallic plates which have been used as electrodes 

 during the decomposition of an electrolyte. Polarised 

 electrodes, when connected by a galvanometer, give a 

 current which they did not give before being polarised. 

 By this current the plates are discharged again and 

 returned to their original state of equality. 



This depolarising current is indeed a most delicate 

 means of discovering previous decomposition. I have 

 really ascertained that under favourable conditions one 

 can observe the polarisation produced during some 

 seconds by a current which decomposes one milligram 

 of water in a century. 



Products of decomposition cannot appear at the elec- 

 trodes without motions of the constituent molecules of 

 the electrolyte throughout the whole length of the liquid. 

 This subject has been studied very carefully and for a 



