Frontispiece of Nollet's Essai sur l'electricité des corps
Electricity and electrical phenomena presented a major conceptual problem for 18th-century experimental philosophers, who were tasked with understanding not only the nature of electricity and how it moved, but how (or, in some cases, whether) it related to light, fire, magnetism, lightning, sparks, shocks, phosphoresence, nervous phenomena, and the attractive and repulsive phenomena associated with electrically charged objects. It was unclear whether electricity and the forces it exerted (what we would think of as charged particles and their fields) were one and the same thing, or how electricity moved about, or how it moved through materials such as glass, air, or vacuum. The relationship between all of these phenomena and the differing electrical properties of different materials, not to mention electricity’s finicky response to changes in ambient humidity all made electricity an extremely complicated thing to study. On the surface, Coulomb’s 19th-century late-18th-century law (the force of attraction or repulsion is proportional to the product of charges of bodies divided by the square of the distance between them) might seem like a logical extrapolation from Newton’s law of gravitation (the force of attraction is proportional to the product of the masses of bodies divided by the square of the distance between them). Taking into account the experimental difficulties, however, it might also seem miraculous.
Unlike astronomy, the study of electricity remained without any quantitative basis for a long time. Instead, natural philosophers attempted to develop qualitative schemes that were capable of explaining all of the various observations and experimental phenomena associated with electricity. By the middle of the 18th century, a number of kinds of experimental apparatus and canonical experiments had been developed, which often doubled as popular entertainments.
Between 1730 and 1750, the vanguard of experimentation and electrical philosophy was held by French electricians, and particularly Charles François de Cisternay Dufay (1698-1739) and his protege, the Abbé Jean Antoine Nollet (1700-1770). Dufay was born into an influential military family and served in the military himself, and became a member of the Paris Academy of Sciences in 1723 under the sponsorship of Academy’s leading philosopher René Antoine Ferchault de Réaumur. In 1732 Dufay was given the prestigious position of Intendant of the Jardin du Roi (King’s Garden).
Dufay, who deployed mechanistic (“Cartesian”) philosophical explanations for phenomena (as opposed to disembodied “Newtonian” forces), began his studies with chemical phosphorescence, demonstrating that most bodies can be made phosphorescent (thereby depressing the market for phorphors). He went on to discover that most bodies could also be electrified, thereby suggesting the ubiquity of electricity in matter. He also established the previously dubious phenomenon of electrical repulsion (often thought to be attraction from other bodies), establishing the pattern where attracting electrical objects come into contact and subsequently repulse each other. Finally, he distinguished two kinds of electricity—those created by “vitreous” substances and those created by “resinous” substances.
In 1733, Dufay took on Nollet as a student. Nollet, a peasant, had trained for the ministry but migrated into the sciences. After a year or two under Dufay at the Jardin du Roi, Nollet entered Réaumur’s laboratory. In 1735 he became a private lecturer; in 1739 the Academy admitted him as an adjoint mechanician, and he collected a variety of private and university positions thereafter. He was a thorough experimenter, a careful philospher, and an active debunker of electrical cures.
Between 1745 and the mid-1750s, Nollet’s philosophical explanations of electrical phenomena (the système Nollet) became the dominant explanation of electrical attraction, repulsion, and other phenomena such as sparks and phosphorescence. Rejecting Dufay’s two types of electricity, Nollet instead explained electrical phenomena by recourse to the idea that electricity flowed outward from irregularly spaced pores in electrified objects (effluent streams), and that attractive phenomena could be explained in terms of a general affluent flow of matter pushing inward on the object between the outward directed effluent streams.
An illustration of Nollet's system; below, the first illustration of a Leyden jar experiment
By 1750, Nollet’s system had begun to be challenged by the American electrician Benjamin Franklin’s system of electrical excesses and defecits (electrification “plus” and “minus”), which was advocated by Nollet’s opponents in the clique of the Comte de Buffon, who had taken over the Intendancy of the Jardin du Roi after Dufay’s untimely death. Nollet was able to deflect his opponents’ initial attacks, but as Franklin’s system was refined to answer objections, particularly those offered by Nollet and his supporters; and as it provided more satisfying explanations for the “shocking” new breed of Leyden jar experiments (though the Leyden jar inventor, Pieter van Musschenbroek remained an adherent to Nollet’s system); it was adopted by a new generation of European electricians, particularly in a newly electrically ascendant Italy.
The history of Dufay and Nollet is interesting to me, because, as with so much 18th-century natural philosophy, it’s not really possible to identify the good guys or the bad guys or to see the emergence of truth. Although Franklin’s system “won”, it was often deployed using inferior arguments by those with professional axes to grind. Although Nollet’s system might seem like a step backward from Dufay, he was certainly understood at the time as—and could easily be argued to be—a progressive figure.
The source on electrical experimentation in the 17th and 18th centuries remains John Heilbron’s appropriately titled 1979 work, Electricity in the 17th and 18th Centuries. Lamentably out-of-print from University of California Press, the book is a crucial resource for anyone studying the physical sciences and natural philosophy in this period. The language can be a little ahistorical at times, but the material is nevertheless meticulously researched and well-presented. I’m going to go ahead and throw it on the Canon page. Also, click on the pictures to go to a page with scanned plates from Nollet’s works.