3.0 The Birth of Electromagnetism

"Newtonian" Point Particle Action-At-A-Distance Electromagnetism Starts with Coulomb

“Nature and Nature’s laws lay hid in night:
God said, Let Newton be! and all was light.”

Alexander Pope (1688–1744)

At the end of the eighteenth century, Newtonian physics was preeminent, but it was the point-mass, action-at-a-distance interpretation of Newton by Cotes, Boscovich, and others that reigned supreme. The accepted archetype of physical theories employed point masses interacting at a distance without any intermediary agency. The early theory of electricity and magnetism would be heavily influenced by this thinking. Electromagnetic science would not arise from theoretical speculation alone, however, but rather from innovative experimental techniques and meticulous measurements. The pioneer in this new experimental and mathematical science of electricity and magnetism was a French military engineer with a long career noted for integrity and professional competence, Charles Augustin de Coulomb (1736–1806) [[i]].

Where others speculated about inverse-square force laws for electricity, Coulomb’s unequivocally proved the relationship [[ii]]. To make his discoveries, he invented a delicate torsion balance. Realizing that when a wire is twisted, the angle of deflection is proportional to the torque, Coulomb suspended electrified bodies and magnets from a fine wire and measured the resulting minute electric and magnetic forces. He further implemented a pendulum torsion balance where the change in the frequency of oscillation allowed a measurement of the difference between the background magnetic field and the field he aimed to measure [[iii]].

Figure 3.1: Coulomb employed a delicate torsion balance to demonstrate that the electrical forces follow a similar relationship to gravitational forces [[iv], [v]].

Using the torsion balance of Figure 3.1 and similar instruments, Coulomb discovered that the electric force between electrified objects is remarkably similar to the gravitational force between masses discovered by Newton. Replace Newton’s gravitational constant (G) with an electric constant (k = 1/4πε₀; more about that presently), and replace the magnitude of the masses (m₁ and m₂) with the magnitude of the charges (q₁ and q₂). Coulomb’s inverse-square electric force law is quite similar to Newton’s Universal Law of Gravitation.

In 1789, the French Revolution disrupted Coulomb’s investigations. He rather prudently fled Paris, thus escaping the guillotine that awaited such notables as Antoine Lavoisier (1743–1794), the father of modern chemistry. Leaving his equipment behind, he was unable to resume work for more than a decade. He continued working on the properties of magnets only in 1801, but was unable to complete his work before his health failed [[vi]]. Coulomb died in 1806, but soon others would extend his pioneering measurements to the case of moving charges or currents. His important discoveries are why Coulomb’s name has been forever memorialized as the unit of electric charge.

Next time, 3.1 The Discovery of Electromagnetism.

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References

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[i] Whittaker, Edmund, A History of Theories of Æther and Electricity, Vol. 1 (New York:  Harper and Brothers, 1960), p. 53. Originally published 1910.

[ii] Spavieri, G., G.T. Gillies, and M. Rodriguez, “Physical Implications of Coulomb’s Law,” Metrologia vol. 41, 2004, pp. S159-S170. See: http://staff.ustc.edu.cn/~ephy/HI_group/courses/CoulombsLaw.pdf.

[iii] Assis, Andre Koch Torres, and Louis L. Bucciarelli, Coulomb’s Memoirs on Torsion, Electricity, and Magnetism Translated Into English, Montreal, Quebec, Canada 2023.

[iv] Oil on canvas of Charles-Augustin de Coulomb (1736–1806) made in 1894 by the French painter Louis Hierle (1856–1906). According to Assis, it is based on an earlier oil painting of Coulomb made between 1803 and 1806 by an unknown artist. Some attribute the original to Hippolyte Lecomte (1781–1857). See: https://commons.wikimedia.org/wiki/File:Charles_de_coulomb.jpg  

[v] http://en.wikipedia.org/wiki/Image:Bcoulomb.png, Public Domain, https://commons.wikimedia.org/w/index.php?curid=938164

[vi] O’Reilly, Michael Francis (writing as Brother Potamian), and James Joseph Walsh, Makers of Electricity, New York: Fordham University Press, 1909, pp. 188-204.