532 



NATURE 



{Oct. 6, 1887 



some degree of certainty as Tertiary beds ht situ. The sands at 

 Netley Heath and at Chipstead have a remarkable Upper Bag- 

 shot facies. Those at Headley do not present such a strong 

 character in this respect, but I have no hesitation in referring 

 them on lithological grounds to the Bagshot series. 



Wellington College, Berks, September 27. A. Irving. 



MODERN VIEWS OF ELECTRICITY} 



Part I. 



I. 



IT is often said that we do not know what electricity is, 

 and there is a considerable amount of truth in the 

 statement. It is not so true, however, as it was some 

 twenty years ago. Some things are beginning to be 

 known about it ; and though modern views are tentative, 

 and may well require modification, nevertheless some 

 progress has been made. I shall endeavour in this 

 lecture to set forth as best I may the position of thinkers 

 on electrical subjects at the present time. 



It will at once strike you that the whole subject of 

 electricity as at present known is too gigantic for anyone 

 to make an attempt to compass it in a single lecture, even 

 though he assume on the part of his audience a perfect 

 acquaintance with all the ordinary phenomena ; and you 

 will admit that it is much better to limit one's self definitely 

 at the beginning to some one branch than by attempting 

 too broad and discursive a survey to risk slurring the 

 whole and becoming totally unintelligible. 



I begin by saying that the whole subject of electricity 

 is divisible for purposes of classification into four great 

 branches. 



(i) Electricity at rest, or static electricity : wherein are 

 studied all the phenomena belonging to stresses and 

 strains in insulating or dielectric media brought about 

 by the neighbourhood of electric charges or electrified 

 bodies at rest immersed therein ; together with the modes 

 of exciting such electric charges and the laws of their 

 interactions. 



(2) Electricity in locomotion, or current electricity : 

 wherein are discussed all the phenomena set up in 

 metallic conductors, in chemical compounds, and in 

 dielectric media, by the passage of electricity through 

 them ; together with the modes of setting electricity in 

 continuous motion and the laws of its flow. 



(3) Electricity in rotation, or magnetism : wherein are 

 discussed the phenomena belonging to electricity in 

 whirling or vortex motion, the modes of exciting such 

 whirls, the stresses and strains produced by them, and 

 the laws of their interaction. 



(4) Electricity in vibration, or radiation : wherein are 

 discussed the propagation of periodic or undulatory dis- 

 turbances through various kinds of media, the laws 

 regulating wave velocity, wave-length, reflection, inter- 

 ference, dispersion, polarization, and a multitude of 

 phenomena studied for a long time under the heading 

 " Light." Although this is the most abstruse and difficult 

 portion of electrical science, a certain fraction of it has 

 been known to us longer than any other branch, and has 

 been studied under special advantages, because of our 

 happening to possess a special sense-organ for its 

 appreciation. 



Now, with some qualms of regret I have decided to 

 refrain from speaking to you about any one of these great 

 and comprehensive groups except the first. It is hopeless 

 to attempt more ; and even the small portion of that 

 on which I shall touch will tax the time at our disposal to 

 the utmost, and I must assume acquaintance with the 

 elementary facts in order to proceed to their elucidation. 



The great names in connexion with our progress in 



^ Expansion of a lecture delivered by Dr. Oliver Lodge, partly at the 

 London Institution on January i, 1885, and partly at the Midland Institute, 

 Birmingh.-im, November 15, 1886, but not hitherto published. 



knowledge as to the real nature of electricity, irrespectiv 

 of a mere study and extension of its known facts, are 



Franklin, Cavendish, Faraday, Maxwell. 



To these, indeed, you may feel impelled to add th 

 tremendous name of Thomson ; but one has som 

 delicacy in attempting to estimate the work of livin 

 philosophers, and as Maxwell has been very explicit i 

 acknowledging his indebtedness to his illustrious cor 

 temporary, whose work will in the course of nature hav 

 to be criticised and appraised by far abler hands tha 

 mine and by the philosophers of generations yet unbori 

 we may well afford to abstain from minute consideratior 

 and accept for the present the name of Maxwell as repn 

 sentative of the great English school of mathematic; 

 physicists, under whose influence, Cambridge, in th 

 pride of having reared them, is awaking to new an 

 energetic scientific life, and whose splendid achievement 

 will shine out in the future as the glory of this centun 



The views concerning electrification which I shall ti 

 to explain are in some sense a development of thos 

 originally propounded by that most remarkable mai 

 Benjamin Franklin. The accurate and acute exper 

 menting of Cavendish laid the foundation for the moder 

 theory of electricity ; but, as he worked for himself rathe 

 than for the race, and as moreover he was in this matter ft 

 in advance of his time, Faraday had to go over the sara 

 ground again, with extensions and additions peculiar 1 

 himself and corresponding to the greater field of inform; 

 tion at his disposal three-quarters of a century late 

 Both these men, and especially Faraday, so lived amor 

 phenomena that they yielded up their hidden secrets 1 

 them in a way unintelligible to ordinary workers ; b' 

 while they themselves arrived at truth by processes th: 

 savour of intuition, they were unable always to expre 

 themselves intelligibly to their contemporaries and 

 make the inner meaning of their facts and speculatioi 

 understood. Then comes Maxwell, with his keen pen 

 tration and great grasp of thought combined with math 

 matical subtlety and power of expression ; he assimilat \ 

 the facts, sympathizes with the philosophic but untutort: 

 modes of expression invented by Faraday, links tl 

 theorems of Green and Stokes and Thomson to the fac; 

 of Faraday, and from the union there arises the youi 

 modern science of electricity, whose infancy at tJ 

 present time is so vigorous and so promising that we a 

 all looking forward to the near future in eager hope ai 

 expectation of some greater and still more magnifice 

 generalization. 



You know well that there have been fluid or mater 

 theories of electricity for the past century ; you kno 

 moreover, that there has been a reaction against the 

 There was even a tendency a few years back to deny t 

 material nature of electricity and assert its position asi 

 form of energy. This was doubtless due to an analogic' 

 and natural, though unjustifiable, feeling that just 

 sound and heat and light had shown themselves to 

 forms of energy so in due time would electricity also, 

 such were the expectation, it has not been justified 

 the event. Electricity may possibly be a form 

 matter — it is not a form of energy. It is quite tr 

 that electricity under pressiwe or in motion repreg 

 energy, but the same thing is true of water or 

 and we do not therefore deny them to be forms of mj 

 Understand the sense in which I use the word electr 

 Electrification is a result of work done, and is 

 certainly a form of energy ; it can be created and 

 stroyed by an act of work. But electricity— none is e 1 

 created or destroyed, it is simply moved and strained 

 matter. No one ever exhibited a trace of positive el< 

 city without there being somewhere in its inime 

 neighbourhood an equal quantity of negative. 



This is the first great law, expressible in a vane 

 ways : as, for instance, by saying that total algebraic! 



e tr 



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