**A Gallery of Electromagnetic Personalities 2...**

## Laplace, Poisson, Fourier

**Pierre-Simon Laplace** (1749-1827) was the son of a peasant farmer. He showed his mathematical ability early and at eighteen he went to Paris to make his way in mathematics. A letter on the principles of mechanics written to d'Alembert gained him a professorship at the École Militaire. His discovery that the attractive force of a mass upon a particle could be obtained
directly by differentiating a single potential function laid the mathematical foundation for the analysis of heat, magnetism, and
electricity. Because he was apolitical he escaped imprisonment and the guillotine during the Revolution. He was later made a marquis.

**Siméon-Denis Poisson** (1781-1849) was forced into the study of medicine by his family but he abandoned it for mathematics. In Paris at the École Polytechnique, Laplace and Lagrange were his instructors, and later his lifelong friends. Poisson's most
important work concerned the application of mathematics to electricity and magnetism, and other areas of physics. In 1812 he published a paper which contained many of the most useful laws of electrostatics and his theory that electricity is made up of two fluids, in which like and unlike repel and attract each other.

**Joseph Fourier **(1768-1830) was a French mathematician who was also a prominent figure in the politics of the Napoleonic
era. He exerted a strong influence on mathematical physics through his analysis of the conduction of heat in solid bodies. He also
served as cultural ambassador to Egypt during the French occupation and achieved a reputation as an Egyptologist who was responsible
for amassing the collection of Egyptian antiquities for the Louvre.

## Ørsted, Ohm, Green

**Hans Christian Ørsted** (1777-1851), a son of the village apothecary on a small Baltic island without a school, was educated by the villagers and went on to become a professor at the University of Copenhagen. In 1820 he was performing a classroom demonstration of the heating effect of electric currents when he observed the deflection of a nearby compass. Within a short while he announced this astounding discovery in a four-page Latin pamphlet he distributed to scientists throughout Europe. He had discovered a connection between electricity and magnetism. Photo: Ørsted's compass.

**Georg Simon Ohm** (1789-1854) was the German physicist who in 1827 discovered the law that the current flow through a conductor is proportional to the voltage and inversely proportional to the resistance. Ohm was then a professor of mathematics in Cologne.
His work was coldly received. The Prussian minister of education announced that "a professor who preached such heresies was unworthy
to teach science." Ohm resigned his post, went into academic exile for several years, and then left Prussia and became a professor in Bavaria. Photo: Ohm's Apparatus.

**George Green** (1793-1841) was a self-taught mathematician who worked in his family's windmill until the age of forty. In 1828 he privately published* "An Essay on the Application of Mathematical Analysis to the Theories of Electricity and Magnetism"* in which he extended the work of Poisson to obtain a general method of solution for the potential. It gained him admittance to Cambridge as an undergraduate in 1833. He graduated in 1837 and was elected to a fellowship in 1839, two years before his death. (The fellowship was for bachelors; Green qualified because he had never formally married the mother of his six children.) Photography had not appeared yet and the circumstances of his life were such that no portrait was ever made. Thus no likeness of Green is available. He is commemorated by a plaque in the floor of Westminster Abbey, in front of the memorial to Newton. The other scientists so honored are Maxwell, Faraday, Kelvin and Dirac. Green's plaque (shown above) is adorned with a representation of a windmill.