Experimental Researches in Electricity, Volume 1

Summary

Experimental Researches in Electricity gathers the numbered papers that Michael Faraday read to the Royal Society and printed in its Philosophical Transactions, in which he discovered electromagnetic induction, showed that all kinds of electricity are one, and found the quantitative laws of electrolysis. Volume 1, first published in London in 1839, collects the first fourteen Series, written between 1831 and 1838, in 1,748 numbered paragraphs, with a preface, an index and plates; the library text is the 1849 second edition reprint. Faraday wrote the Series as a running laboratory record, and he says in the preface that he reprinted them as written rather than recast them. The First Series (read November 1831) opens by asking why, if a current produces magnetism, magnetism should not produce a current. Faraday winds two coils of wire on a block of wood and on an iron ring, connects one to a battery and the other to a galvanometer, and finds a brief current in the second coil only when the first is switched on or off. He then produces currents by moving magnets in and out of a coil, names the effect magneto-electric induction, proposes an electro-tonic state of matter, explains Arago's rotating-disc puzzle, and builds the first generator, a copper disc turned between the poles of the Royal Society's great magnet. The Second Series obtains currents from the earth's own magnetism. The Third Series (1833) compares five kinds of electricity: voltaic, common or frictional, magneto-electric, thermo-electric and animal electricity from the torpedo fish, testing each for heat, magnetism, chemical decomposition, sparks and physiological effects, and concludes that they differ only in quantity and intensity. The Fourth to Seventh Series turn to electrochemistry. Faraday shows that many solids conduct only when melted, argues that decomposition is a property of the current acting along the liquid rather than of attraction to the poles, and, with new terms of his own (electrode, anode, cathode, electrolyte, ion, anion, cation), proves that the amount of a substance decomposed is proportional to the quantity of electricity passed, and that the weights released are chemical equivalents. He devises the volta-electrometer to measure that quantity. The Eighth Series examines the voltaic pile and argues that its power is chemical in origin; the Ninth describes the extra current induced by a current in its own wire; the Tenth improves the battery. The Eleventh to Fourteenth Series develop a new theory: induction is an action of contiguous particles of the matter between charged bodies, not action at a distance, and different insulators have a specific inductive capacity. These papers laid the experimental foundation for the field theory later given mathematical form by James Clerk Maxwell.

Top Lessons

• Asking the symmetrical question

  Faraday began from a simple reversal: since Oersted had shown that an electric current makes magnetism, could magnetism make a current? Years of failed attempts preceded the discovery that the effect appears only when something changes. The First Series shows how a good question and patient experiment can open a new science.

• Naming things well

  In the Seventh Series Faraday coins electrode, anode, cathode, electrolyte and ion, choosing words that would not commit him to a theory he could not prove. He worries that the old word pole suggests attraction to a point. Careful vocabulary is shown as part of careful science.

• One force in many forms

  The Third Series patiently tests five kinds of electricity, from the battery to the torpedo fish, for the same set of effects. Faraday concludes that they differ only in quantity and intensity, not in nature. The method, a table of effects checked one by one, is a model of building a general conclusion from many particular trials.

• Measurement turns a mystery into a law

  By inventing the volta-electrometer, which measures electricity by the gas it releases from water, Faraday could show that the same quantity of electricity always decomposes chemically equivalent amounts of different substances. A qualitative curiosity became a quantitative law linking electricity and chemical combination.

Verified Quotes

Medical Lens

The Researches are a work of physics and chemistry, but they touch medicine at two points. In the Third Series Faraday includes the physiological effects of each kind of electricity, a frog's convulsions, the shock, the taste on the tongue and the flash before the eyes, and he treats animal electricity from the torpedo and the electric eel (gymnotus) as identical in nature with that of the battery, closing the debate opened by Galvani and Volta over whether living tissue has its own electricity. Indirectly, his induction coil gave medicine the interrupted induced current that physicians such as Guillaume Duchenne in France applied in the 1850s as faradization, used in neurology to stimulate muscles and, through the later nineteenth century and into the First World War, in the treatment of hysterical paralysis and some cases of shell shock. That later medical history lies outside the book itself.

• Third Series, paragraphs 279, 332 and 347

  Physiological effects of voltaic, common and magneto-electricity: shocks, convulsions of a frog, sensations on the tongue and flashes before the eyes.

• Third Series, Section V (paragraphs 351-359)

  Animal electricity from the torpedo and gymnotus compared with other kinds and found identical in nature.

• First Series, paragraphs 6-33

  The interwound coils and the welded iron ring (paragraph 27) whose interrupted secondary current later became the basis of medical faradization.