Ampere’s Alternate Interpretation of Electromagnetism

A. K. T. Assis is a Brazilian scholar who has written some intriguing books on physics and the history of physics. He has very generously made all these books available for free access on his website – https://www.ifi.unicamp.br/~assis/books.htm.

I have been flipping through the book Ampere’s Electrodynamics by Prof. Assis. It requires a much closer study, but I wanted to write about one thing that stood out for me.

All this while, I had thought of the development of electromagnetism as a linear timeline. I had thought that starting with Oersted’s experiment, other scientists had added bit by bit to the understanding of electromagnetic phenomena, until Maxwell synthesised all the knowledge into one single theory. This book showed me that the actual history was very different.

It seems that there were many differences of opinion between Ampere and the other prominent scientists of the time regarding how to interpret the phenomena. The following snapshot from the book’s Contents pages promises an enticing discussion of these scientific controversies.

The most remarkable aspect of Ampere’s theory was that he imagined all magnetic phenomena as arising from electric currents. In this, almost all his contemporaries disagreed with him vehemently.

For Ampere, there was no ‘magnetic field’ – it was simply a manifestation of an interaction between currents. He hypothesised that there were circular electric currents inside magnets and inside the Earth, which we know today to be true.

The following muse (edited for readability) from Ampere’s writings is a striking example of the role of imagination and creativity in science:

“Suppose we had known that a magnetic needle is influenced by an electric current into a position perpendicular to the wire before knowing that a magnetic needle points to the geographical north. Then, would not the simplest idea and the one that would occur immediately to anyone who wanted to explain it be that there is an electric current inside the Earth?

Andre Marie Ampere

Assis’ book also includes a complete English translation of Ampere’s classic work written in 1826, Theory of Electrodynamic Phenomena, Uniquely Deduced from Experience.

I hope to write more on this when I do manage to study this book in detail.

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