Lives of the electricians

by William T. Jeans

In 1849 eminent natural philosophers were studying this subject in England, France, and Germany, and it was expected that the investigation of diamagnetic phenomena would rapidly throw some new light upon the molecular forces which determine the conditions of the material creation. In allusion to this expectation, Tyndall said in 1850, that as nature acts by general laws, to which the terms great and small are unknown, it cannot be doubted that the modifications of magnetic force, exhibited by bits of copperas and sugar in the magnetic field, display themselves on a large scale in the crust of the earth itself, and as a lump of stratified grit, though a magnetic material, could be made, on account of its planes of stratification, to act as if it were diamagnetic, he suggested that this element might have some influence in determining the varying position of the magnetic poles of the earth—a subject which still perplexes the scientific world. Not only has the north magnetic pole gradually been changing its position, as shown by the records of three centuries, but, according to Barlow, every place has a magnetic pole and equator of its own; and according to Faraday the earth is a great magnet, whose power, as estimated by Gauss, is equal to that which would be conferred if every cubic yard of it contained six one-pound magnets; the sum of the force being thus equal to 8,464,000,000,000,000,000,000 such magnets. “The disposition of this magnetic force is not regular,” said Faraday, “nor are there any points on the surface which can be properly called poles: still the regions of polarity are in high north and south latitudes; and these are connected by lines of magnetic force (being the lines of direction), which, generally speaking, rise out of the earth in one (magnetic) hemisphere, and passing in various directions over the equatorial regions into the other hemisphere, there enter into the earth to complete the known circuit of power.”

It was in connection with his investigations on this subject that Prof. Tyndall first saw Prof. Faraday. Returning from Marburg in 1850, he called at the Royal Institution and sent in his card, together with a copy of a paper he had prepared, giving the results of his experiments on magne-crystallic action. Prof. Faraday conversed with him for half-an-hour, and being then on the point of publishing one of his papers on magne-crystallic action, he appended to it a flattering reference to the notes which Tyndall had placed in his hands.

Tyndall went back to Germany, where he worked for another year. In the beginning of 1851 he went to Berlin, where, he says, Prof. Magnus had made his name famous by physical researches of all kinds. “On April 28th, 1851, I first saw this Professor on his own doorstep in Berlin. His aspect won my immediate regard, which was strengthened to affection by our subsequent intercourse. He gave me a working place in his laboratory, and it was there I carried out my investigations on diamagnetism and magnecrystallic action published in the Philosophical Magazine for September, 1851. Among the other eminent scientific men whom I met at Berlin was Ehrenberg, with whom I had various conversations on microscopic organisms. I also made the acquaintance of Riess, the foremost exponent of frictional electricity, who more than once opposed to Faraday’s radicalism his own conservatism as regarded electric theory. Du Bois-Reymond was there at the time, full of power, both physical and mental. His fame had been everywhere noised abroad in connection with his researches on animal electricity. Du Bois-Reymond became perpetual secretary to the Academy of Sciences, Berlin. From Professor Magnus, and from Clausius, Wiedemann, and Poggendorff, I received every mark of kindness, and formed with some of them enduring friendships. Helmholtz was at this time in Königsberg. He had written his renowned essay on the “Conservation of Energy,” which I afterward translated. Helmholtz had, too, just finished his experiments on the velocity of nervous transmission, proving this velocity, which had previously been regarded as instantaneous, or, at all events, as equal to that of electricity, to be, in the nerves of the frog, only 93 ft. a second, or about one-twelfth of the velocity of sound in air of the ordinary temperature. In his own house I had the honour of an interview with Humboldt. He rallied me on having contracted the habit of smoking in Germany, his knowledge on this head being derived from my little paper on a water-jet, where the noise produced by the rupture of a film between the wet lips of a smoker is referred to. He gave me various messages to Faraday, declaring his belief that he (Faraday) had referred the annual and diurnal variation of the declination of the magnetic needle to their true cause—the variation of the magnetic condition of the oxygen of the atmosphere. I was interested to learn from Humboldt himself that, though so large a portion of his life had been spent in France, he never published a French essay without having it first revised by a Frenchman. In those days I not unfrequently found it necessary to subject myself to a process which I called depolarisation. My brain, intent on its subjects, used to acquire a set, resembling the rigid polarity of a steel magnet. It lost the pliancy needful for free conversation, and to recover this I used to walk occasionally to Charlottenburg or elsewhere. From my experiences at that time I derived the notion that hard thinking and fleet talking do not run together.”

Prof. Tyndall was exceptionally fortunate in getting so easily and so early into the friendship of such eminent men of science. In those days to form such eminent acquaintances was no small achievement for a young Irishman; but on the other hand, he had fully earned this distinction by the vigour and originality with which he attacked the latest and most perplexing problem of that time. During the five years that had elapsed since Faraday discovered diamagnetism, the subject had been investigated by the greatest scientists in England, France, and Germany, and no one had done so much to elucidate it as Prof. Tyndall. In order to master that subject he began in November, 1850, an investigation of the laws of magnetic attractions. The laws of magnetic action at distances in comparison with which the thickness of the magnet vanishes, had long been known, but the laws of magnetic action at short distances, where the thickness of the magnet comes fully into play, had not previously been subjected to reliable experiments, and were therefore at that time a perplexing matter of speculation. That desideratum he now supplied. He found, among other things, that the mutual attraction of a magnet and a sphere of soft iron, when both are separated by a small fixed distance, is directly proportional to the square of the strength of the magnet, and that the mutual attraction of a magnet of constant strength and a sphere of soft iron is inversely proportional to the distance between them.

Next year (1851) he published the results of further investigations into the relations between magnetism and diamagnetism. He found that the laws which govern magnetism and diamagnetism are identical, that the superior attraction or repulsion of a mass in any particular direction is due to the direction in which the material particles are arranged most closely together, that the forces exerted are attractive or repulsive according as the particles are magnetic or diamagnetic, and that this law is applicable to matter in general.

A paper on “The Polarity of Bismuth,” which might be regarded as a temporary instalment of his diamagnetic researches, ended with the remark that during this inquiry he had changed his mind too often to be over-confident now in the conclusion at which he had arrived. Part of the time he was a hearty subscriber to the opinion of Faraday that there existed no proof of diamagnetic polarity; and if, he said, “I now differ from that great man, it is with an honest wish to be set right, if through any unconscious bias of my own I have been led either into errors of reasoning or mis-statements of fact.”

The theory of diamagnetism was still an apple of discord in the scientific world; and although Prof. Tyndall used the language of deference rather than of doubt, he did not allow the subject to remain in a state of uncertainty. He continued his researches in Berlin, in the private laboratory of Prof. Magnus, who afforded him every possible facility for carrying on experiments, and took a lively interest in the investigation. The result was the confirmation of his previous impression that the action of crystals within the range of a magnet’s influence (technically called the “magnetic field”) was due to peculiarities of molecular arrangement. He found, for example, that a crystal of carbonate of iron, which, when suspended in the magnetic field, showed a certain deportment, could be pounded into the finest dust, and the particles could be so put together again that the mass would exhibit the same deportment as before.

Dr. Bence Jones, the Secretary of the Royal Institution, who had heard of Tyndall in Berlin in 1851, afterwards invited him to give a Friday evening lecture at the Royal Institution. “I went,” he says, “not without fear and trembling, for the Royal Institution was to me a kind of dragon’s den, where tact and strength would be necessary to save me from destruction.” The lecture, which was delivered on February 11th, 1853, was “On the Influence of Material Aggregation upon the Manifestations of Force,” and it gave a beautiful and simple exposition of the principles of magnetic and diamagnetic action discovered by himself, the chief being that the line of greatest density is that of strongest magnetic power. In the course of his lecture he pointed out that anything which increases density increases magnetic power; and upon that principle he contended that the local action of the sun upon the earth’s crust must influence in some degree the diurnal range of the magnetic needle, which Faraday, on the other hand, attributed to the modification of our atmosphere by the sun’s rays. While thus endeavouring to upset Faraday’s theory, he concluded by saying: “This evening’s discourse is, in some measure, connected with this locality, and thinking thus, I am led to inquire wherein the true value of a scientific discovery consists? Not in its immediate results alone, but in the prospect which it opens to intellectual activity, in the hopes which it excites, in the vigour which it awakens. The discovery which led to the results brought before you to-night was of this character. That magnet was the physical birthplace of these results; and if they possess any value they are to be regarded as the returning crumbs of that bread which in 1846 was cast so liberally upon the waters. I rejoice in the opportunity here afforded me of offering my tribute to the greatest worker of the age, and of laying some of the blossoms of that prolific tree which he planted at the feet of the great discoverer of diamagnetism.” At the conclusion of the lecture Faraday quitted his usual seat, and crossing the theatre to the corner where the lecturer stood, cordially shook him by the hand and congratulated him on his success. A second lecture was delivered by him on June 3rd, 1853, “On some of the Eruptive Phenomena of Iceland,” and a month later he was unanimously elected Professor of Natural Philosophy in the Royal Institution.

Some years previously he had read in a serial publication an account of Davy’s experiments on radiant heat at the Royal Institution, and he remembered ever after the longing then excited in him to be able to do something of the same kind. Now he was to occupy a position in which he should use, in his own lectures, the same apparatus of which illustrations were given in the magazine article that had fired his youthful ambition. To that position he was promoted on the recommendation of Faraday, and respecting his appointment he himself said: “I was tempted at the time to go elsewhere, but a strong attraction drew me here. It was his (Faraday’s) friendship that caused me to value my position here more highly than any other.”

While the controversy respecting magnetic and diamagnetic hypotheses was still raging, Faraday delivered a lecture at the Royal Institution early in 1855 with the express object of cautioning the investigators of scientific truths against placing too much confidence on any hypothesis. He stated that every year of increased experience had taught him more and more to distrust the theories he had once adhered to; and his present impression with regard to existing Magnetic and Electrical hypotheses was, that they were very unsatisfactory, and that the propounders of them had been following in a wrong track. As an instance of the obstacles which erroneous hypotheses throw in the way of scientific discovery, he mentioned the unsuccessful attempts that had been made in this country to educe magnetism from electricity, until Oersted showed the simple way. He said that the identity of magnetism and electricity had been strongly impressed upon the minds of all: when he came to the Royal Institution, as an assistant in the laboratory, he saw Davy, Wollaston, and Young trying by every way that suggested itself to them to produce magnetic effects from an electric current; but, having their minds diverted from the true course by their existing hypotheses, it did not occur to them to solve the point by holding a wire, through which an electric current was passing, over a suspended magnetic needle—the experiment by which Oersted afterwards proved, by the deflection of the needle, the magnetic property of an electric current.