**BERNOULLI Daniil** (Bernoulli Daniel, 1700 — 1782) — one of the first academicians St. Petersburg AN, and then its honorary member (1733 — 1782); worked in the field of physiology, medicine, the higher mathematics and mechanics. I. Bernoulli's AN was born in a family of the Swiss mathematician, professor Groningen un-that, afterwards the honorary member St. Petersburg. Got medical education in Switzerland and Germany.

In 1721 D. Bernoulli defended the dissertation on physiology of breath, in a cut tried to apply mathematical methods to a research. In 1725 by the invitation of the president St. Petersburg L. L. Blyumentrost's AN of D. Bernoulli arrived to Russia and was a part of academy.

Here it in 1725 — 1727 occupied department of physiology, and in 1727 — 1733 — department of mechanics. Since 1733 — professor of physiology in Basel, and after the death of the father (1748) became his successor at department of mechanics Basel un-that (since 1750). The circle of scientific interests of D. Bernoulli was very wide. His compositions on an optic nerve, on the movement of muscles were one of the first works on medicine published St. Petersburg by AN. He pointed to dependence of height of reduction of a muscle on length of muscle fibers (the so-called principle of Bernoulli — see. Muscles , physiology).

In 1727 — 1729 a series of works of D. Bernoulli is published in Latin «Comments» of academy, edges formed the basis of one of classical works of world science — his book «Hydrodynamics or Notes about Forces and the Movements of Liquids» (1738). In it the constitutive equation of the stationary movement of true liquid output by it — the so-called equation of Bernoulli in hydrodynamics is published. As the movement of low-viscous liquids is close to hydrodynamics of the movement of true liquid, Bernoulli's equation is applicable also for studying of blood circulation: it allows to apply theoretically reasonable methods of calculation to calculation of some sizes which not always are giving in to pilot study and also to prove methodical methods of studying of a hemodynamics and some ways of theoretical synthesis of the obtained data (see. Hemodynamics ).

D. Bernoulli is the author of a method of the numerical solution of the algebraic equations by means of returnable ranks, and also works on probability theory, on the differential equations, on a gas theory. It possesses attempt of development of kinetic idea of gases.

The majority of the scientific works (47 of 75) performed by D. Bernoulli in 1728 — 1778 are published in editions St. Petersburg by AN.

**Works:** De respiratione, diss., Basil, 1721; Hydrodynamica, sive de viribus et motibus fluidorum commentarii, Strassburg, 1738; Versuch einer neuen Theorie der Bewegung der Muskeln, Phys. u. med. Abhandl. d. k. Akad. d. Wissensch. in Petersb., Bd 1, S. 3, Riga, 1782.

**Bibliography:** Raynov T. I. Daniil Bernoulli and his work in the St. Petersburg Academy of Sciences, Vestn. Academy of Sciences of the USSR, No. 7-8, page 84, 1938.

*V. A. Ponomarchuk.*