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Bioelectromagnetism

In September 1831, Faraday tried to solve the problem of producing electricity from magnetism.

Trough a series of experiments, he discovered electromagnetic induction, the results which were

presented to the Royal Society on November 24, 1831. His successful results of electromagnetic induc­

tion spawned through Europe. Faraday’s law of electromagnetic induction was the basis of the trans­

former, which is the converter of mechanical energy into electric energy. Joseph Henry (1797–1878), an

American physicist, the frst secretary of the Smithsonian Institution, Washington, DC, also discovered

that a change in magnetism can produce electric currents. Electromagnetic induction was discovered

independently by Faraday and Henry. Later, this invention became a very important contribution to

bioelectric research.

Apart from Faraday’s contribution, the discussion turned on to Oersted’s discovery and the progress

of instrumentation. Afer Oersted’s discovery, it gradually began the development of the instrumen­

tation which can support the study of electrophysiology in bioelectromagnetism. Oersted’s fnding

was that the defection of the needle could be used to indicate electric current strength, the appear­

ance of the magnetic efect on an electric current, which led to the appearance of the frst galvanom­

eter. Two months afer Oersted’s discovery, in September 1820, Johann Salemo Christoph Schweigger

(1779–1857), professor of Chemistry at University of Hall, Germany, using of wire helix and a compass

needle, developed an instrument for detecting and measuring electric current, called electromagnetic

multiplier (multiplicator) or galvanometer. Te needle was placed at the center of a rectangle consisting

of many turns of insulated wire. Many electrical instruments depended on the operation of this simple

principle and were employed for the measurement of electricity. Schweigger’s instrument was refned

by Leopoldo Nobili (1784–1835), a preeminent Italian physicist, professor of Physics at University of

Florence, Italy, in 1825 (Nobili, 1825). Te refned instrument was called astatic galvanometer. Tis

astatic galvanometer employs a double coil of 72 turns wound in a form of fgure-eight. Te efect of

the geomagnetic feld was compensated by placing two identical magnetic needles connected on the

same suspension with opposite polarity. Tis became the most important instrument for measuring

the electric current strength in the feld of electrophysiology (Possenti and Selleri, 2017). Using the

astatic galvanometer, Nobili measured and recorded animal electricity such as the electric current

from the neuromuscular preparation of frogs. Nobili’s astatic galvanometer opened the instrumental

era of electrophysiology.

As can be seen above, the history of bioelectromagnetism ran closely in parallel to the developmental

history of the measuring instruments of bioelectric signals. With the development of the instruments,

electrophysiology became its own feld in the frst half of the nineteenth century.

Faraday predicted experimentally the existence of electromagnetic waves afer the discovery of elec­

tromagnetic induction. James Clerk Maxwell (1831–1879), physicist and mathematician at Scotland,

published the theory of electromagnetic waves in 1864. Tis theory predicted the existence of a whole

spectrum of electromagnetic waves with the speed of light (3 × 10⁸m/s), and Heinrich Rudolf Hertz

(1857–1894), German physicist, professor at the University of Karlsruhe, demonstrated experimentally

the existence of it, which contributed to the age of electromagnetic waves technology. In 1888, Hertz won

the Matteucci Medal which was named afer Carlo Matteucci. In the 1830s, Carlo Matteucci (1811–1868),

an Italian physiologist, a graduate of University of Bologna and professor of Physics of University of

Pisa, had shown that the discharge of the electric organs of the ray was controlled by a special structure,

the electric lobe. At the time when he published the work on the electric fsh, he also repeated Galvani’s

and Nobili’s animal electricity experiments. Using Nobili’s astatic galvanometer, he recorded electrical

activity from the heart of a frog in 1842. He developed the idea of animal electricity and found that dur­

ing the leg’s tetanic contractions, the measured current was driven by a diference in electrical poten­

tial between an injured and uninjured nerve. He was a pioneer in the study of bioelectricity. Trough

the experiments by Galvani and Matteucci, the action potential was discovered in cardiac muscle and

nerves. In particular, Matteucci’s work came to the attention of Johannes Peter Müller (1801–1858), a

German physiologist, professor at the University of Berlin. Müller found the capacitive properties of

tissues and the anisotropy of muscle conductance.