Against the current

Andre-Marie Ampere
June 21, 1996

This scholarly work is, as James Hofmann makes clear, a biography of a rather unhappy man, who also happened to be an important scientist. His first wife died after they had been married only three years, his second marriage was a disaster and his relations with his children were an almost constant source of pain. We often forget, when thinking of distinguished scientists that they may have lived in troubled times.

This was certainly the case with Andre-Marie Amp re, born into a prosperous family in Lyon in 1775, just before the French Revolution. His father was guillotined in 1792 and for the remainder of his life, until he died in 1836, he had to endure the kaleidoscopic changes in the political institutions of France, and their effects on his prospects as an employee of the state. These conditions, which similarly affected Laplace, Lagrange, Poisson, Fresnel, Biot and Savart no doubt explain much of the back-biting in the scientific establishment, and the bitterness of the struggles to establish scientific priority that are revealed by Hofmann in his account of the first part of Ampere's career.

Had Ampere died on his 50th birthday he would almost certainly have been forgotten. Though he occasionally revealed flashes of inspiration, his unclear style, betraying a lack of intellectual discipline, could very easily be attributed to his lack of any formal training. This lack, though it did not hamper a much greater scientist, Faraday, also emerges in Amp re's attitude to experiment, where his preoccupation, one might almost say obsession, with the metaphysics of experimentation continually stood in his way. All this is described very clearly by Hofmann, and so is Amp re's devout Catholic upbringing, his loss of faith and his final return to the church; that, as Hofmann gently hints, might have been politically correct under the restored Bourbons. Although this may all appeal to the social historian, what a scientific reader will want to know is, what was Ampere's great achievement and how did someone so apparently disorganised intellectually, come to achieve it?

Here the book is less satisfying. The reader has to wait until well over halfway through it, and even then the achievement hardly becomes clear. It is true that Ampere invented the term "electrodynamics" to describe the effect of an electric current on a magnet that had been discovered by Oersted, but that barely seems enough. Was it Ampere's insistence that all magnetic effects were due to electric currents?

Was it his demonstration that the magnetic effects of a current loop and a magnetic sheet would be identical?

Was it his discussion of the force acting between two parallel long wires each carrying a current, the result that we now used to define the unit of current, the ampere, called after him? If this were the case how did it differ from the formulae usually associated with Biot and Savart? Somehow in this book Ampere's achievement is never related to the scientific context in which it was made.

Whatever it was, one thing is clear: how greatly Ampere was hampered by his lack of the notion of a magnetic field, a concept which only developed in the years after his death, beginning with Faraday's ideas and finally being consummated in Maxwell's equations. It is hard for us, equipped as we are with field theories and vector methods, to appreciate how difficult the unravelling of the complexity of the forces exerted by currents on magnets and other currents must have been for Amp re and his contemporaries.

The reader who wants only to understand Ampere's scientific achievement would do better to read the half-dozen pages that E.T.Whittaker devotes to Ampere in his History of the Theories of Aether and Electricity (1951).

F. N. H. Robinson is emeritus fellow, St Catherine's College, Oxford.

Andre-Marie Ampere: Enlightenment and Electrodynamics

Author - James R. Hofmann
ISBN - 0 521 56220 1
Publisher - Cambridge University Press
Price - £40.00
Pages - 406

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