Experimental Researches in Electricity

Overview

Experimental Researches in Electricity is a thousand pages and it is not a book in the ordinary sense. It is thirty papers read to the Royal Society between 1831 and 1855, collected in three volumes, and numbered in one continuous sequence of paragraphs that runs past three thousand. Faraday cites himself by paragraph number throughout, so the whole work is cross-referenced like a legal code.

Nobody reads it end to end. It is a reference work, and the way in is to take one series at a time.

Two features make it strange among the classics of physics. There is no mathematics. Faraday had almost none, and his arguments proceed entirely through described experiments and physical pictures. And the writing is unusually honest about process: he reports the experiments that failed, states what an experiment has not established, and marks his speculations as speculations, sometimes publishing them separately so that they cannot contaminate the evidence.

The man is part of the interest. Faraday was the son of a blacksmith, left school at thirteen, was apprenticed to a bookbinder, and educated himself by reading the books he was binding. He got into science by taking notes at Humphry Davy’s public lectures, binding them beautifully and sending them to Davy with a request for work. He later refused a knighthood and twice refused the presidency of the Royal Society.

The argument

Series I, 1831: induction. The founding experiment and the one to read first. Ørsted had shown ten years earlier that a current produces magnetism. Everyone assumed the converse must hold, and everyone had failed to find it, because they were looking for a steady effect from a steady arrangement.

Faraday wound two separate coils on an iron ring, connected one to a battery and the other to a galvanometer, and saw the needle kick when he closed the circuit, settle back to nothing while the current flowed, and kick the other way when he broke it. That is a transformer, and it announces the principle: the effect depends on change. He went on to produce the same result by thrusting a magnet into a coil, and then, in the experiment that matters most industrially, by rotating a copper disc between the poles of a magnet to produce a continuous current. That is a dynamo, and essentially every watt generated in the world today is generated on this principle.

Series III, 1833: one electricity. At the time it was seriously debated whether the electricity of a voltaic pile, of a friction machine, of a thermocouple and of an electric eel were the same thing. Faraday tested them against every effect he could produce, chemical, magnetic, physiological, and showed that they differ in quantity and intensity and not in kind.

Series V to VIII, 1833 to 1834: electrochemistry. The two laws that carry his name. The amount of a substance liberated at an electrode is proportional to the quantity of electricity passed, and for the same quantity of electricity the amounts of different substances are proportional to their chemical equivalents. This ties the electrical and the chemical together quantitatively and points, though Faraday does not say so, toward a natural unit of charge.

Here he also had to invent the vocabulary, since the existing language assumed a theory he rejected. With William Whewell’s help he coined electrode, anode, cathode, electrolyte, electrolysis, ion, anion and cation, all of which are still in use.

Series XI, 1837: the medium matters. Faraday showed that the capacity of a condenser depends on what is between the plates, a property he called specific inductive capacity. If empty space were merely empty, the material between should make no difference. It does, and this is the beginning of his campaign against action at a distance.

Series XIX, 1845: light and magnetism. After years of failed attempts he sent polarised light through a piece of heavy glass in a strong magnetic field and found the plane of polarisation rotated. His diary entry that night says he had succeeded in magnetising a ray of light. It is the first experimental connection between optics and electromagnetism, and it is the seed of the eventual recognition that light is an electromagnetic wave.

Series XX and XXI, 1845 to 1846: diamagnetism. Faraday found that substances previously thought non-magnetic are in fact weakly repelled by a magnetic field, and concluded that magnetism acts on everything. Bismuth is the standard example.

Lines of force. Running through all of it is the picture Faraday could not prove and would not drop. He imagined space threaded with curved lines of force, physically real, along which the action travels, so that a magnet does not reach across a gap but modifies the space around it. Contemporaries with mathematics thought this the naive substitute of a man who lacked their training. Maxwell, who had the mathematics, said the opposite: Faraday saw lines traversing all space where the mathematicians saw centres of force attracting at a distance, and translating him into equations produced the field theory that is now the whole subject.

How to read it

Read Series I first, in full. It is perhaps forty pages, it is completely intelligible without mathematics, and you can follow every step of a great discovery as it happens.

Then choose by interest: Series III for method, Series V and VII for the electrochemistry and the birth of the vocabulary, Series XIX for the magnetic rotation of light.

Read it as a record of practice rather than a statement of results. What is instructive is the way Faraday varies one thing at a time, interrogates a negative result rather than discarding it, and refuses to let an attractive hypothesis stand in for a demonstration.

Notice how he handles speculation. Faraday had bold and largely correct intuitions about the unity of forces and about the field, and he kept them out of the experimental papers or flagged them explicitly. That discipline is more unusual than it sounds.

If the volumes are too much, his Chemical History of a Candle, the Christmas lectures for children, is short, in print, and shows the same mind doing something easier.

Questions it raises

• Faraday worked without mathematics and saw what mathematically trained contemporaries missed. What was the physical picture doing for him that equations were not doing for them?
• Lines of force were unprovable when he proposed them and he insisted they were real. When is that kind of commitment good science and when is it stubbornness?
• Induction depends on change rather than on state. Why did that take ten years to find when everyone was looking?
• The electrochemical laws imply a natural unit of charge. Why did Faraday not draw that conclusion?
• He publishes his failures. What does a literature look like that does not?
• Maxwell said he was translating Faraday into mathematics. Is a physical intuition the same discovery once it has been formalised, or a different one?