ticles of matter; he finds difficulty in grasping the notion of the action of induction at a distance, and therefore he endeavours to explain these effects by a kind of polarity which he assumes to exist in the contiguous particles of matter lying between the electrified body and the furthest point at which the induced electricity can be detected. He does not seem to see that the difficulty, doubtless existing, of understanding how forces can act at a distance is not diminished by reducing the distance through which the force acts from millions of miles to millionths of an inch! It is almost impossible to give a true estimate of the value of Faraday's theoretic considerations upon this subject; they are frequently obscure, and in general they are only intelligible from his own point of view. Nevertheless, true to his firm belief in facts, he works his way by thousands of experiments through the mazes of his hypotheses, and it is these wonderfully accurate and suggestive experiments that remain as permanent and all-important records of his labours on electrical induction.

In 1838 he experimented at the Adelaide Gallery upon the electric shocks given off by a Gymnotus, the first one which had been brought to London. He proved, as Gay Lussac had done for the Torpedo, that the electric shock given by the Gymnotus was able to produce magnetic actions, chemical decompositions, and to give a spark; he estimates the quantity of electricity discharged by the fish to equal that given off from a battery of fifteen Leyden jars containing 3,500 square inches coated on both sides and charged to its highest degree! In writing to Dumas on the subject of the relation of electricity to life, Faraday says, 'As living beings evolve heat and 'certainly the same heat as our fires, why should they not also 'evolve electricity equally identical with that of our electric 'machines? But if heat produced during life and necessary 'to life is nevertheless not the cause of life, why should elec'tricity be the cause of life? Like heat, or chemical action, electricity is an instrument of life, and nothing more.' interesting glimpse into his daily and domestic life at this time is given by his niece Miss Reid, who then lived with Mr. and Mrs. Faraday at the Institution :

An

In the earlier days of the Juvenile Lectures he used to encourage me to tell him everything that struck me, and where my difficulties lay when I did not understand him fully. In the next lecture he would enlarge on those especial points, and he would tell me my remarks had helped him to make things clear to the young ones. never mortified me by wondering at my ignorance, never seemed to think how stupid I was. I might begin at the very beginning again and again; his patience and kindness were unfailing.

He

'A visit to the laboratory used to be a treat when the busy time of the day was over.

'We often found him hard at work on experiments connected with his researches, his apron full of holes. If very busy he would merely give a nod, and aunt would sit down quietly by me in the distance, till presently he would make a note on his slate and turn round to us for a talk; or perhaps he would agree to come upstairs to finish the evening with a game at bagatelle, stipulating for half-an-hour's quiet work first to finish his experiment.

'When dull and dispirited, as sometimes he was to an extreme degree, my aunt used to carry him off to Brighton, or somewhere for a few days, and they generally came back refreshed and invigorated. Often of an evening they would go to the Zoological Gardens and find interest in all the animals, especially the new arrivals, though he was always much diverted by the tricks of the monkeys. We have seen him laugh till the tears ran down his cheeks as he watched them. He never missed seeing the wonderful sights of the day-acrobats and tumblers, giants and dwarfs; even Punch and Judy was an unfailing source of delight, whether he looked at the performance or at the admiring gaping crowd.'

The strain which the labour of the last ten years had put upon Faraday proved too much for his frame to bear. Long ago he had complained of loss of memory, and now in 1841, when he was fifty years of age, giddiness and mental depression altogether stopped his experimentalising. For the four following years, with the exception of an inquiry into the cause of electricity produced in Armstrong's steam electrical machine, no researches in electricity were published. He rested entirely for a year and went to Switzerland for three months. When he began to work again he returned to his investigation of the liquefaction of gases.

'In different ways,' says his Biographer, 'he showed much of his character during this period of rest. The journal he kept of his Swiss tour is full of kindness and gentleness and beauty. It shows his excessive neatness. It has the different mountain flowers which he gathered in his walks fixed in it, as few but Faraday himself could have fixed them. His letters are free from the slightest sign of mental disease. His only illness was overwork, and his only remedy was

rest.'

That his bodily strength was not impaired is certain from the fact that one day he started alone from the Baths of Leuk over the Gemmi, past Kandersteg and Frütigen, all the way to Thun, doing the forty-five miles in ten and a half hours, without much fatigue and with no ill effects. He adds in his diary, so that I think my strength cannot be bad or my reasoning (?) very insufficient. I would gladly give half this 'strength for as much memory, but-what have I to do with

⚫ that? Be thankful.' Here some flowers from the top of the Gemmi pass were fastened into the journal with great skill and taste.

In the year 1845 begins the second period of Faraday's researches in electricity: this lasted ten years. The three great results which he obtained were what he called the magnetisation of light,' the magnetic condition of all matter,' and atmospheric magnetism.'

The first of these discoveries was the result of his theoretical speculations on the connexion of the forces of nature.

'I have long held an opinion, almost amounting to a conviction, in common, I believe, with many other lovers of natural knowledge, that the various forms under which the forces of matter are made manifest have one common origin; or in other words, are so directly related and mutually dependent that they are convertible, as it were, into one another, and possess equivalents of power in their action."

He turned to the examination of the action of magnets on a beam of polarised light, and after many vain attempts he at length succeeded in proving, first by using a piece of his dense glass, that the plane of polarisation of the ray passing through the glass is rotated when the glass is placed between the poles of a powerful magnet. Many friends to whom Faraday showed this experiment believed that his explanation was incorrect, and that the torsion of the polarised ray depended upon the glass itself, setting up for a time the same conditions which we find producing permanent circular polarisation in such substances as sugar and quartz. Faraday did not accept this explanation as the true one, but in justice to his friends he put it to his invariable touchstone of truth-experiment; and the reply was so far in his favour that the action was proved not to be identical with that of quartz or any other circularly polarising substance. And for this reason that the ray of light on being passed backwards and forwards through the magnetised glass, not only suffered no diminution in its angle of rotation, as it would have done had it been quartz, but, on the contrary, its rotatory power became increased; in a ratio directly proportional to the number of times it passed through.

Still Faraday was at last obliged to give up the idea that the ray of light itself was acted upon by the magnet, because he found that whatever interferes with or prevents the displacement of the particles of the glass, likewise impedes the development of the rotatory power by magnetic action, and hence crystallised bodies exhibit this action in but slight degree. In fact the magnetic attraction strained the glass, and the strain produced the power of causing the polarised ray to

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rotate. Now although this power of magnetism was first observed by Faraday with his dense glass, yet he soon noticed that the same effect can be produced by most all transparent substances, with the exception of the gases, and it was this discovery which led to the grand generalisation of the universality of magnetic actions. In other words, that, instead of iron and cobalt being the only magnetic bodies, Faraday showed that all bodies are subject to magnetic influence, being divided into the magnetic and the dia-magnetic, or those which are attracted and those which are repelled by a magnet. In this discovery of the magnetic condition of all matter' we have a striking example of how the experimental philosopher working for a special end often opens out an unexpected and unsought treasure. Faraday was searching for a proof of the action of magnetism on the rays of light. He was obliged to give up the idea that he had found such an action, for he saw that the phenomenon he observed was due to the action of a much wider law, viz., the magnetic condition of all matter. He proved that far from magnetism alone residing in the loadstone, as the ancients believed, all solids and liquids and even gases are subject to the action of the magnet. One set of substances taking like iron a polar direction between the ends of a magnet, viz., one joining the poles; the other set taking an equatorial position at right angles to the line joining the poles of the magnet. The theory of dia-magnetism is one upon which men of science are not yet thoroughly agreed; whether, for instance, it is a force distinct from magnetism, or whether these two conditions of matter are merely relative, all bodies being magnetic in different degrees. Faraday showed that crystallised bodies were affected by dia-magnetism in different directions with different degrees of intensity, and thus opened out the way to a new and complicated field of investigation-magne-crystalline action-since worked out by Plücker, Knoblauch, and Tyndall, and theoretically examined by Sir William Thomson. In concluding his first paper on this subject, Faraday says:

'I cannot conclude this series of researches without remarking how rapidly the knowledge of molecular forces grows upon us, and how strikingly every investigation tends to develop more and more their importance, and their extreme attraction as an object of study. A few years ago magnetism was to us an occult power, affecting only a few bodies; now it is found to influence all bodies, and to possess the most intimate relations with electricity, heat, chemical action, light, crystallisation, and through it with the forces concerned in cohesion; and we may, in the present state of things, well feel urged to continue in our

labours, encouraged by the hope of bringing it into a bond of union with gravity itself.'

Then in 1847 he passed on from the magnetic actions exerted by solid and liquids to the magnetic attractions of gases. Repeating Bancalari's experiments on the magnetism of flames, he proves that even the colourless invisible gases can be shown to exert attraction or repulsive action on the magnet. He inclosed the gases in thin glass bulbs of which he knew the magnetic action, and thus found that of the component gases of the atmosphere oxygen is powerfully magnetic, whereas nitrogen is neither magnetic nor dia-magnetic. Then he compares the magnetism of oxygen with that of sulphate of iron, and finds that for equal bulks oxygen is equally magnetic with a solution of this substance in water containing seventeen times the weight of the oxygen in crystallised proto-sulphate of iron.'

'It is hardly necessary,' he writes, 'for me to say here that this oxygen cannot exist in the atmosphere exerting such a remarkable and high amount of magnetic force without having a most important influence on the disposition of the magnetism of the earth as a planet; especially if we remember that its magnetic condition is greatly altered by variations of its density and by variations of its temperature. I think I see here the real cause of so many variations of that force, which have been, and are now, so carefully watched on different parts of the surface of the globe. The daily variation and the annual variation seem both likely to come under it; also very many of the irregular continual variations, which the photographic process of record renders so beautifully manifest . . . and even magnetic relations and variations which are not yet suspected may be suggested and rendered manifest and measurable in the further development of what I will venture to call Atmospheric Magnetism. I may be over-sanguine in these expectations, but as yet I am sustained in them by their apparent reality, simplicity, and sufficiency of the cause assumed, as it at present appears to my mind.'

Two elaborate papers devoted to this subject were sent to the Royal Society on October 9, and November 19, 1850. The conclusions as to the direct connexion between the daily and annual variation of the earth's magnetism and the magnetic attraction of the atmospheric oxygen varying at different temperatures, has since lost much of their force by the singular and important discovery of the relation doubtless existing between the variation of the magnetic declination and the number of the solar spots. Still there appears to be little doubt that the variation of the magnetism of the atmospheric oxygen, which according to Becquerel is equal to that of a film of iron as thin as writing-paper spread over the earth's