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Definition: Faraday, Michael from Philip's Encyclopedia

English physicist and chemist. Faraday worked as Sir Humphry Davy's assistant at the Royal Institution in London, where, in 1825 he became director of the laboratories. Faraday liquefied chlorine, discovered benzene (1825), and enunciated the laws of electrolysis (Faraday's laws). He also discovered electromagnetic induction, made the first dynamo, built a primitive electric motor, and studied nonconducting materials (dielectrics). The unit of capacitance (the farad) is named after him.


Summary Article: Faraday, Michael (1791-1867) from The Hutchinson Dictionary of Scientific Biography

Place: France

Subject: biography, physics

English physicist and chemist who is often regarded as the greatest experimental scientist of the 1800s. He made pioneering contributions to electricity, inventing the electric motor, electric generator and the transformer, and discovering electromagnetic induction and the laws of electrolysis. He also discovered benzene and was the first to observe that the plane of polarization of light is rotated in a magnetic field.

Faraday was born in Newington, Surrey, on 22 September 1791. His father was a poor blacksmith, who went to London to seek work in the year that Faraday was born. Faraday received only a rudimentary education as a child and although he was literate, he gained little knowledge of mathematics. At the age of 14, he became an apprentice to a bookbinder in London and began to read voraciously. The article on electricity in the Encyclopedia Britannica fascinated him in particular, for it presented the view that electricity is a kind of vibration, an idea that was to remain with Faraday. He also read the works of Antoine Lavoisier and became interested in chemistry, and carried out what scientific experiments he could put together with his limited resources. He was aided by a manual dexterity gained from his trade, which also stood him in great stead in his later experimental work.

In 1810 Faraday was introduced to the City Philosophical Society and there received a basic grounding in science, attending lectures on most aspects of physics and chemistry and carrying out some experimental work. He also attended the Royal Institution, where he was enthralled by the lectures and demonstrations given by Humphry Davy. He made notes eagerly, assembling them at work into finely bound books. In 1812 Faraday came to the end of his apprenticeship and prepared to devote himself to his trade, not expecting to make a career in science. Almost immediately, however, there came an extraordinary stroke of luck. Davy was temporarily blinded by an explosion in a chemistry experiment and asked Faraday to help him until he regained his sight. When he recovered, Faraday sent Davy the bound notes of his lectures. Impressed by the young man, Davy marked him out as his next permanent assistant at the Royal Institution and Faraday took up this post in 1813.

This was remarkably good fortune for Faraday, because Davy was a man of wide-ranging interests and great scientific insight as well as a brilliant exponent of ideas. Furthermore, Davy undertook a tour of France and Italy 1813-15 to visit the leading scientists of the day, including the pioneer of current electricity Alessandro Volta. Faraday accompanied Davy, gaining an immense amount of knowledge, and on his return to London threw himself wholeheartedly into scientific research.

Faraday remained at the Royal Institution and made most of his pioneering discoveries in chemistry and electricity there over the next 20 years. He became a great popularizer of science with his lectures at the Royal Institution, which he began in 1825 and continued until 1862. His fame grew rapidly, soon eclisping even that of Davy, who became embittered as a result. But the strain of his restless pursuit of knowledge told and in 1839 Faraday suffered a breakdown. He never totally recovered but at the instigation of Lord Kelvin, returned to research in 1845 and made his important discoveries of the effect of magnetism on light and developed his field theory. In the 1850s, Faraday's mind began to lose its sharp grip, possibly as a result of low-grade poisoning caused by his chemical researches, and he abandoned research and then finally lecturing. He resigned from the Royal Institution in 1862 and retired to an apartment provided for him at Hampton Court, Middlesex, by Queen Victoria. He died there on 25 August 1867.

Faraday was mainly interested in chemistry during his early years at the Royal Institution. He investigated the effects of including precious metals in steel in 1818, producing high-quality alloys that later stimulated the production of special high-grade steels. Faraday's first serious chemical discoveries were made in 1820, when he prepared the chlorides of carbon - C2Cl6 from ethane and C2Cl4 from ethylene (ethene) - substitution reactions that anticipated the work a few years later by Jean Baptiste Dumas. In 1823 Faraday produced liquid chlorine by heating crystals of chlorine hydrate (Cl2.8H2O) in an inverted U-tube, one limb of which was heated and the other placed in a freezing mixture (liquefaction resulted because of the high pressure of the gas cooled below its relatively high critical temperature). He then liquefied other gases, including sulphur dioxide, hydrogen sulphide, nitrous oxide (dinitrogen oxide), chlorine dioxide, cyanogen, and hydrogen bromide. After the production of liquid carbon dioxide in 1825, Faraday used this coolant to liquefy such gases as ethylene (ethene), phosphine, silicon tetrafluoride, and boron trifluoride.

In the same year (1825) he made his greatest contribution to organic chemistry, the isolation of benzene from gas oils. He also worked out the empirical formula of naphthalene and prepared various sulphonic acids - later to have great importance in the industries devoted to dyestuffs and detergents. It was also at about this time that Faraday demonstrated the use of platinum as a catalyst and showed the importance in chemical reactions of surfaces and inhibitors - again foreshadowing a huge area of the modern chemical industry.

But Faraday's interest in science had been initiated by a fascination for electricity and he eventually combined the knowledge that he gained of this subject with chemistry to produce the basic laws of electrolysis in 1833. His researches, summed up in Faraday's laws of electrolysis, established the link between electricity and chemical affinity, one of the most fundamental concepts in science. It was Faraday who coined the terms anode, cathode, cation, anion, electrode, and electrolyte. He postulated that during the electrolysis of an aqueous electrolyte, positively charged cations move towards the negatively charged cathode and negatively charged anions migrate to the positively charged anode. At each electrode the ions are discharged according to the following rules:

(a) the quantity of a substance produced is proportional to the amount of electricity passed;

(b) the relative quantities of different substances produced by the same amount of electricity are proportional to their equivalent weights (that is, the relative atomic mass divided by the oxidation state or valency).

But his first major electrical discovery was made much earlier, in 1821, only a year after Hans Oersted had discovered with a compass needle that a current of electricity flowing through a wire produces a magnetic field. Faraday was asked to investigate the phenomenon of electromagnetism by the editor of the Philosophical Magazine, who hoped that Faraday would elucidate the facts of the situation following the wild theories and opinions that Oersted's sensational discovery had aroused. Faraday conceived that circular lines of magnetic force are produced around the wire to explain the orientation of Oersted's compass needle, and therefore set about devising an apparatus that would demonstrate this by causing a magnet to revolve around an electric current. He succeeded in October 1821 with an elaborate device consisting of two vessels of mercury connected to a battery. Above the vessels and connected to each other were suspended a magnet and a wire; these were free to move and dipped just below the surface of the mercury. In the mercury were fixed a wire and a magnet respectively. When the current was switched on, it flowed through both the fixed and free wires, generating a magnetic field in them. This caused the free magnet to revolve around the fixed wire, and the free wire to revolve around the fixed magnet.

This was a brilliant demonstration of the conversion of electrical energy into motive force, for it showed that either the conductor or the magnet could be made to move. In this experiment, Faraday demonstrated the basic principles governing the electric motor and although practical motors subsequently developed had a very different form to Faraday's apparatus, he is nevertheless usually credited with the invention of the electric motor.

Faraday's conviction that an electric current gave rise to lines of magnetic force arose from his idea that electricity was a form of vibration and not a moving fluid. He believed that electricity was a state of varying strain in the molecules of the conductor, and this gave rise to a similar strain in the medium surrounding the conductor. It was reasonable to consider therefore that the transmitted strain might set up a similar strain in the molecules of another nearby conductor - that a magnetic field might bring about an electric current in the reverse of the electromagnetic effect discovered by Oersted.

Faraday hunted for this effect from 1824 onwards, expecting to find that a magnetic field would induce a steady electric current in a conductor. In 1824, François Arago found that a rotating nonmagnetic disc, specifically of copper, caused the deflection of a magnetic needle placed above it. This was in fact a demonstration of electromagnetic induction, but nobody at that time could explain Arago's wheel (as it was called). Faraday eventually succeeded in producing induction in 1831. In August of that year, he wound two coils around an iron bar and connected one to a battery and the other to a galvanometer. Nothing happened when the current flowed through the first coil, but Faraday noticed that the galvanometer gave a kick whenever the current was switched on or off. Faraday found an immediate explanation with his lines of force. If the lines of force were cut - that is, if the magnetic field changed - then an electric current would be induced in a conductor placed within the magnetic field. The iron core in fact helped to concentrate the magnetic field, as Faraday later came to understand, and a current was induced in the second coil by the magnetic field momentarily set up as current entered or left the first coil. With this device, Faraday had discovered the transformer, a modern transformer being no different in essence even though the alternating current required had not then been discovered.

Faraday is thus also credited with the simultaneous discovery of electromagnetic induction, though the same discovery had been made in the same way by Joseph Henry in 1830. However, busy teaching, Henry had not been able to publish his findings before Faraday did, although both men are now credited with the independent discovery of induction.

Faraday's insight enabled him to make another great discovery soon afterwards. He realized that the motion of the copper wheel relative to the magnet in Arago's experiment caused an electric current to flow in the disc, which in turn set up a magnetic field and deflected the magnet. He set about constructing a similar device in which the current produced could be led off, and in October 1831 built the first electric generator. This consisted of a copper disc that was rotated between the poles of a magnet; Faraday touched wires to the edge and centre of the disc and connected them to a galvanometer, which registered a steady current. This was the first electric generator, and generators employing coils and magnets in the same way as modern generators were developed by others over the next two years.

Faraday's next discoveries in electricity, apart from his major contribution to electrochemistry, were to show in 1832 that an electrostatic charge gives rise to the same effects as current electricity, thus proving that there is no basic difference between them. Then in 1837 he investigated electrostatic force and demonstrated that it consists of a field of curved lines of force, and that different substances take up different amounts of electric charge when subjected to an electric field. This led Faraday to conceive of specific inductive capacity. In 1838, he proposed a theory of electricity based on his discoveries that elaborated his idea of varying strain in molecules. In a good conductor, a rapid build-up and breakdown of strain took place, transferring energy quickly from one molecule to the next. This also accounted for the decomposition of compounds in electrolysis. At the same time, Faraday rejected the notion that electricity involved the movement of any kind of electrical fluid. In this, he was wrong (because the motion of electrons is involved) but in that this motion causes a rapid transfer of electrical energy through a conductor, Faraday's ideas were valid.

Faraday's theory was not taken seriously by many scientists, but his concept of the line of force was developed mathematically by Kelvin. In 1845, he suggested that Faraday investigate the action of electricity on polarized light. Faraday had in fact already carried out such experiments with no success, but this could have been because electrical forces were not strong. Faraday now used an electromagnet to give a strong magnetic field instead and found that it causes the plane of polarization to rotate, the angle of rotation being proportional to the strength of the magnetic field.

Several further discoveries resulted from this experiment. Faraday realized that the glass block used to transmit the beam of light must also transmit the magnetic field, and he noticed that the glass tended to set itself at right angles to the poles of the magnet rather than lining up with it as an iron bar would. Faraday showed that the differing responses of substances to a magnetic field depended on the distribution of the lines of force through them, and not on the induction of different poles. He called materials that are attracted to a magnetic field paramagnetic, and those that are repulsed diamagnetic. Faraday then went on to point out that the energy of a magnet is in the field around it and not in the magnet itself, and he extended this basic conception of field theory to electrical and gravitational systems.

Finally Faraday considered the nature of light and in 1846 arrived at a form of the electromagnetic theory of light that was later developed by James Clerk Maxwell. In a brilliant demonstration of both his intuition and foresight, Faraday said ‘The view which I am so bold to put forth considers radiation as a high species of vibration in the lines of force which are known to connect particles, and also masses of matter, together. It endeavours to dismiss the ether but not the vibrations.’ It was a bold view, for no scientist until Albert Einstein was to take such a daring step.

Michael Faraday was a scientific genius of a most extraordinary kind. Without any mathematical ability at all, he succeeded in making the basic discoveries on which virtually all our uses of electricity depend and also in conceiving the fundamental nature of magnetism and, to a degree, of electricity and light. He owed this extraordinary degree of insight to an amazing talent for producing valid pictorial interpretations of the workings of nature. Faraday himself was a modest man, content to serve science as best he could without undue reward, and he declined both a knighthood and the presidency of the Royal Society. Characteristically, he also refused to take part in the preparation of poison gas for use in the Crimean War. His many achievements are honoured in the use of his name in science, the farad being the SI unit of capacitance and the Faraday constant being the quantity of electricity required to liberate a standard amount of substance in electrolysis.

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