196 Chapter 13
many others. After the announcement of Ø rsted ’ s discovery in 1820, Andr é -Marie Amp è re
wrote his son that “ since I have heard of the beautiful discovery of M. Oersted ... I have
thought of it constantly. ”^3 Amp è re was surprised because Coulomb ’ s work had seemed
to demonstrate that any influence of electricity on magnetism was impossible because
they were two essentially dissimilar fluids, and hence were incapable of interacting.
Further, circular lines of force had no precedent in Newtonian physics, which was usually
understood to exclude transverse forces. Amp è re gave precise mathematical form to
Ø rsted ’ s discovery, bringing the quantitative power of French science to this child of
Naturphilosophie. Reconsidering Coulomb ’ s arguments, Amp è re theorized that magnetism
was caused by electric currents and described the mutual forces between two parallel
current-carrying wires in what came to be called “ Amp è re ’ s law. ”
In 1821, at the request of his friend Richard Phillips, Faraday published an extensive
historical survey of the new field of electromagnetism, which showed that he considered
history an essential part of what he called “ philosophy, ” not fond of the new coinages
“ physicist ” and “ scientist. ” Indeed, Faraday ’ s historical reconstruction helped him correct
his initial misunderstanding of Ø rsted ’ s discovery as simple attraction or repulsion, rather
than a circular force acting transversely.^4 As was the case with Descartes, Faraday ’ s cor-
respondence shows him moving between many fields, addressing questions of chemistry,
sound, and electromagnetism. For instance, his letters to Charles Gaspard de la Rive began
in 1818 with their shared interest in “ singing tubes, ” heated vials of hydrogen and other
gases that produce roars and even musical tones, about which Faraday had written a paper.^5
In September 1821, Faraday ’ s subsequent letter to de la Rive combined descriptions of
investigations of steel alloys with discussion of Amp è re ’ s theories, alongside Faraday ’ s
experimental demonstration that electromagnetism could rotate a wire: the first electric
motor ( figure 13.1 ).^6
Faraday ’ s correspondence with Amp è re showed their mutual respect as well as
Faraday ’ s hesitation to accept the literal physicality of Amp è re ’ s microscopic theory of
electromagnetism, in which each molecule was a tiny current loop. For Faraday in 1821,
“ we have no proof of the materiality of electricity, or of the existence of any current
through the wire. ”^7 As an alternative to “ the passage of matter ” being the cause of the
electromagnetic effects, as Amp è re had argued, Faraday now suggests “ the induction of a
particular state of its [the conducting wire ’ s] parts, ” the first mention of the intermolecular
“ state ” that would figure so significantly in his later thoughts on what he eventually called
the “ electro-tonic state. ”^8
Having learned that electric currents give rise to magnetic effects, Faraday and many
others sought what seemed the symmetric and complementary effect: if indeed electro-
magnetism were a unified, symmetric whole, magnetism ought likewise to cause electric
effects. Yet despite many attempts in the following decade, no one could find any such
effect. Its eventual discovery as electromagnetic induction was preceded by Faraday ’ s
return to questions of sound, which clearly helped him find this elusive phenomenon,