Benjamin Franklin (17.01.1706 - 17.04.1790) was an American physicist and a political and public figure. He was born in Boston. He was self-educated. In 1727 he founded his own printing house in Philadelphia. He published (1729-48) the Pennsylvania Gazette. In 1731 he founded the first public library in the USA, in 1743 the American Philosophical Society, and in 1751 the University of Pennsylvania. In 1737 — 53 he was postmaster of Pennsylvania, and in 1753 —74 of the North American colonies. He played a significant part in the struggle of the North American colonies for independence, took part in drawing up the Declaration of Independence and in framing the constitution of the USA, and spoke out against the oppression of Black people and against slavery.
His main scientific work was in the field of electricity. In 1746 — 54 he carried out a series of experimental studies that brought him wide fame. He explained the action of the Leyden jar, constructed the first parallel-plate capacitor, consisting of two parallel metal plates separated by a layer of glass, invented the lightning rod in 1750, and proved in 1753 the electrical nature of lightning (the kite experiment) and the identity of terrestrial and atmospheric electricity.
He developed (1750) a theory of electrical phenomena — the so-called “unitary theory”, according to which electricity is a special subtle fluid permeating all bodies. Every uncharged, neutral body always contains a certain quantity of “electric fluid”. If for any reason an excess of it appears in a body, the body is charged positively; when it is deficient, negatively. In this theory of Franklin the concept of positive and negative electricity (charge) and their designation, “+” and “-”, were introduced for the first time. On the basis of his theory he explained the phenomena he observed.
Franklin's unitary theory contained the law of conservation of electric charge. Franklin set out his studies in letters (1747 — 54) to P. Collinson, a Fellow of the Royal Society, who published them. The letters became widely known and had great success in Europe.
His work also concerned the thermal conductivity of bodies, in particular metals, the propagation of sound in water and in air, and so on. He was the author of a number of technical inventions, in particular the use of an electric spark to explode gunpowder.
A Fellow of the Royal Society (1756) and of the St Petersburg Academy of Sciences (1789).