Daniel Bernoulli (8.02.1700-17.03.1782) was a mathematician and physicist, one of the members of the famous Bernoulli dynasty. He was the son of J. Bernoulli. He was born in Groningen. He graduated from the University of Basel (1716). In 1725-33 he worked at the St Petersburg Academy of Sciences, occupying himself at first with physiology and from 1730 heading the chair of pure mathematics. In 1733 he returned to Basel, where he took charge first of the chair of anatomy and botany and from 1750 of the chair of experimental physics. He kept close ties with the St Petersburg Academy of Sciences, however, remaining its honorary member and publishing part of his work in its editions.
His principal work in physics, “Hydrodynamica”, published in 1738 in Strasbourg (Bernoulli began writing it while still in St Petersburg in 1728-29), contains the physical foundations of the mechanics of fluids. In this work Bernoulli introduces for the first time the concept of work (“absolute potency”), uses the concept of efficiency (without, it is true, defining it explicitly), formulates the well-known equation of the steady motion of an ideal fluid (Bernoulli's equation), which is in essence a particular case of the law of conservation of mechanical energy, and sets out the ideas of the kinetic theory of gases. Together with L. Euler he is the creator of theoretical hydrodynamics.
He held to the hypothesis that heat is the motion of the small particles of a body. Starting from the hypothesis of the molecular structure of matter, he was the first to give a theoretical explanation of the Boyle–Mariotte law. In 1760, with the aid of an electrometer of his own construction, he came to the conclusion that the force of interaction between electric charges is inversely proportional to the square of the distance between them. He gave magnets (1743) their horseshoe shape.
An honorary member of the Berlin and Paris (1748) academies of sciences and of the Royal Society (1750).