Faraday

“ Faraday, with his curved lines of electric force, and his dielectric efficiency of air and of liquid and solid insulators, resuscitated the idea of a medium through which, and not only through which but by which, forces of attraction or repulsion, seemingly acting at a distance, are transmitted. ”

“ Faraday looks, and rightly looks, into the heart of the decomposing body itself; he sees, and rightly sees, active within it the forces which produce the decomposition, and he rejects, and rightly rejects, the notion of external attraction; but beyond the hypothesis of decompositions and recompositions, enunciated and developed by Grothuss and Davy, he does not, I think, help us to any definite conception as to how the force reaches the decomposing mass and acts within it. Nor, indeed, can this be done, until we know the true physical process which underlies what we call an electric current. ”

“ Nevertheless, after Faraday’s discovery of the different specific inductive capacities of different insulators, twenty years passed before it was generally accepted in Continental Europe. But before his death, in 1867, he had succeeded in inspiring the rising generation of the scientific world with something approaching to faith that electric force is transmitted by a medium called ether, of which, as had been believed by the whole scientific world for forty years,285 light and radiant heat are transverse vibrations. ”

“ For instance, Faraday, in his mind’s eye, saw lines of force traversing all space where the mathematicians saw centres of force attracting at a distance. Faraday saw a medium where they saw nothing but distance. Faraday sought the seat of the phenomena in real actions going on in the medium; they were satisfied that they had found it in a power of action at a distance impressed on electric fluids. ”

“ These are Faraday's most massive discoveries, and upon them his fame must mainly rest. But even without them, sufficient would remain to secure for him a high and lasting scientific reputation. We should still have his researches on the liquefaction of gases; on frictional electricity; on the electricity of the gymnotus; on the source of power in the hydro-electric machine, the two last investigations being untouched in the foregoing memoir; on electro-magnetic rotations; on regelation; all his more purely chemical researches, including his discovery of benzol. ”

“ But Faraday at once saw that his induced currents must come into play here, and he immediately obtained them from an iron disk. With a hollow brass ball, moreover, he produced the effects obtained by Mr. Barlow. Iron was in no way necessary: the only condition of success was that the rotating body should be of a character to admit of the formation of currents in its substance: it must, in other words, be a conductor of electricity. The higher the conducting power the more copious were the currents. He now passes from his little brass globe to the globe of the earth. ”

“ Even greater in experiment, while lacking mathematical power, is Faraday, who next enlists our regard. This great man, more than any other investigator, laid the foundations of modern electrical science and art. Moreover he distinctly saw how matter might reveal itself in the ‘radiant’ condition now engaging the study of the foremost inquirers in physics.
Electricity has no instrument more useful in daily life, or in pure research, than the telephone. Now follows a narration by its creator, Professor Bell, of his photophone which transmits speech by a beam of light. ”

“ Faraday thought much over this question of "induction," as it is called, and found himself greatly puzzled to comprehend how a body should act where it is not. At length he satisfied himself by experiment that the interposed obstacle is itself affected by the electricity, and acquires an electro-polar state by which it modifies electric action in its neighbourhood. The amount varies with the nature of the substance, and Faraday estimated it for such dielectrics as sulphur, shellac, or spermaceti, compared with air. ”

“ The wires and the surrounding water act as a Leyden jar, and the retardation of the current predicted by Faraday manifests itself in every message sent by such cables.
The meaning of Faraday in these memoirs on induction and conduction is, as I have said, by no means always clear; and the difficulty will be most felt by those who are best trained in ordinary theoretic conceptions. He does not know the reader’s needs, and he therefore does not meet them. ”

“ The precision with which Faraday describes these results, and the completeness with which he defines the boundaries of his facts, are wonderful. The magnet, for example, must not be passed quite through the coil, but only half through; for if passed wholly through, the needle is stopped as by a blow, and then he shows how this blow results from a reversal of the electric wave in the helix. He next operated with the powerful permanent magnet of the Royal Society, and obtained with it, in an exalted degree, all the foregoing phenomena. ”

“ The power which lifted the mightier eminences, in nearly all cases lifted others to an almost equal height. And so it is with the discoveries of Faraday. As a general rule, the dominant result does not stand alone, but forms the culminating point of a vast and varied mass of inquiry. In this way, round about his great discovery of magneto-electric induction, other weighty labours group themselves. ”

“ The most difficult and abstruse points in connexion with light, heat, electricity, magnetism, and the laws of matter, have been simplified to an extraordinary degree by the force of his sagacity and singular acuteness. As remarkable as his genius for discovery, and for the detection of the hidden operations of nature, is his admirable faculty of exposition. No living man approaches Faraday in the easy power of communicating the results of the most subtle investigation to a miscellaneous audience. ”

“ Faraday, to whom the idea of mere action at a distance was abhorrent, if not unthinkable, conceived of all these forces of attraction and repulsion as effects taking place by something going on in the intervening medium, as effects propagated from point to point continuously through space. In his earlier work on the electromagnetic rotations he had grown to regard the space around the conducting wire as being affected by the so-called current ”

“ But in Faraday’s experiment this indispensable opposition exists within the wire itself. From the nature of a voltaic charge, the two opposite currents necessary to the existence of each other are both accommodated in one wire; and there is no need of another wire placed beside it to contain one of them, in the same way as the Leyden jar must have a positive and a negative surface. The exciting cause can and does produce all the effect which its laws require, independently of any electric excitement of a neighboring body. ”

“ Faraday’s Views.—The two-fluid theory may be said to have held the field until the time when Faraday began his researches on electricity. After he had educated himself by the study of the phenomena of lines of magnetic force in his discoveries on electromagnetic induction, he applied the same conception to electrostatic phenomena, and thus created the notion of lines of electrostatic force and of the important function of the dielectric or non-conductor in sustaining them. ”

“ In conclusion, Faraday brought to bear upon it an argument which, had its full weight and purport been understood at the time, would have instantly decided the controversy. “The contact theory,” he urged, “assumes that a force which is able to overcome powerful resistance, as for instance that of the conductors, good or bad, through which the current passes, and that again of the electrolytic action where bodies are decomposed by it, can arise out of nothing ”

“ The great discoveries of Oersted, Ampère, and Arago had culminated in England in two results: in Faraday’s discovery that the wire which carries an electric current tends to revolve around the pole of a neighbouring magnet; and in Sturgeon’s invention of the soft-iron electromagnet, a core of iron surrounded by a coil of copper wire, capable of acting as a magnet at will when the electric current is transmitted to the coil and so caused to circulate around the iron core. ”

“ Among the greatest triumphs of Faraday was his discovery of the converse of the production of magnetism by electrical current; I mean the production of current by magnetism. After long attempts, he found that if a magnet was moved into, out of, or in the neighborhood of a coil of wire forming a complete circuit, then a current of electricity was induced, as he put it, in the coil during the motion of the magnet. This is the germ of our dynamo-electric machines which to-day supply all the current for our light, power and electric traction. ”

“ Amongst the memorable achievements of the ten days which Faraday devoted to this investigation was the discovery that a current could be induced in a conducting wire simply by moving it in the neighbourhood of a magnet. One form which this experiment took was that of rotating a copper disk between the poles of a powerful electric magnet. He then found that a conductor, the ends of which were connected respectively with the centre and edge of the disk, was traversed by an electric current. ”

“ In the course of this research on induction, Faraday had, as we have seen, been compelled to adopt new ideas, and therefore to adopt new names to denote them. The term dielectric for the medium in or across which the electric forces operate was one of these. ”

“ As this is never found to be the case, Faraday concluded that it is impossible to communicate an absolute charge to matter, and that no portion of matter can by any change of state evolve or render latent one kind of electricity or the other. He therefore regarded induction as 'the essential function both in the first development and the consequent phenomena of electricity'. ”

“ Faraday sometimes spelled the word cathion (Exp. Res. Art. 1351) , as did also Whewell (Hist. of Ind. Sciences, vol. iii. p. 166) .
43 Literally, the travellers, the things which are going.
44 The term induction appears to have been originally used, in contradistinction to contact or conduction, to connote those effects which apparently are in the class of actions at a distance. Thus we may have induction of a charge by a charge, or of a magnet-pole by a magnet-pole. To these Faraday had added the induction of a current by a current, and the induction of a current by a moving magnet. ”

“ The method of Faraday seems to be intimately related to the second of these modes of treatment. He never considers bodies as existing with nothing between them but their distance, and acting on one another according to some function of that distance. He conceives all space as a field of force, the lines of force being in general curved, and those due to any body extending from it on all sides, their directions being modified by the presence of other bodies. ”

“ Faraday grapples with the subject experimentally. By simple intuition he sees that158 action at a distance must be exerted in straight lines. Gravity, he knows, will not turn a corner, but exerts its pull along a right line; hence his aim and effort to ascertain whether electric action ever takes place in curved lines. This once proved, it would follow that the action is carried on by means of a medium surrounding the electrified bodies. His experiments in 1837 reduced, in his opinion, this point to demonstration. ”

“ Faraday saw mentally the rotating disk, under the operation of the magnet, flooded with his induced currents, and from the known laws of interaction between currents and magnets he hoped to deduce the motion observed by Arago. That hope he realised, showing by actual experiment that when his disk rotated currents passed through it, their position and direction being such as must, in accordance with the established laws of electro-magnetic action, produce the observed rotation. ”

“ In 1821, Faraday commenced his studies in this branch of philosophy; which he has since so diligently followed up, that he has been for some years, and is still the first electrician of the age. From the commencement of the present century, discoveries have succeeded each other in regular order and with the most amazing results; and now electricity is regularly employed as a money-getting agent in the process of the electrotype and electro-silvering and gilding; also in the electric telegraph; and in a few years we may possibly see it commonly employed as a source of artificial light. ”

“ Perhaps no better idea of the importance of the discovery thus made by Faraday can be given than will be found in Clerk Maxwell's compendious paragraph on this subject, in his sketch of Faraday, in the Encyclopedia Britannica. It may be said that no one in all the nineteenth century was more capable of appreciating properly the value of Faraday's work than this great electrical mathematician, who laid the firm foundation of mathematical electricity during the latter part of the nineteenth century. ”

“ A Silber-groschen similarly suspended exhibited the same deportment. For a moment I thought this a new discovery; but on looking over the literature of the subject, it appeared that Faraday had observed, multiplied, and explained the same effect during his researches on diamagnetism. His explanation was based upon his own great discovery of magneto-electric currents. The effect is a most singular one. A weight of several pounds of copper may be set spinning between the electro-magnetic poles; the excitement of the magnet instantly stops the rotation. ”