Figure 2.13. Visual perception and the action of pointing a finger, from
L’Homme de René Descartes (1664).
In the late 1700s, the Italian physician Luigi Galvani (1737-1798)
studied the effects of electrical stimulation on animal muscles. He
found that legs severed from dead frogs could twitch when electri-
cally stimulated and hypothesized that muscles move as a result of
internal electrical forces that can be triggered by external electrical
stimulation (see Fig. 2.14). Galvani published his experimental results
and speculations with the Bologna Academy and Institute of Sciences
and Arts in 1791. His essay was written in Latin and is called De
viribus electricitatis in motu musculari, commentarius. This translates
into English as “Commentary on the effects of electricity on muscular
motion.”
Galvani’s nephew, Giovanni Aldini (1762-1834), continued his
uncle’s work and contributed to increased public attention to connec-
tions between electricity and life. Around the same time, another Ital-
ian, Alessandro Volta (1745-1827), invented the first battery. Later,
near the end of the 1800s, the unit of electric potential difference, the
volt, would be named after him.
In the mid-nineteenth century, Scottish physicist James Clerk Max-
well (1831-1879), building on the work of Hans Christian Oersted
(1777-1851), André Ampére (1775-1836), Michael Faraday (1791-
1867), and others, derived a set of elegant mathematical relations that
provided a unified description of electricity and magnetism. Even
light could now be understood as a propagating wave of electromag-
netic energy. Electricity was getting really big, and increasingly cen-
tral to all of physics.
As electricity became more a focus of experimental investigation,