René Descartes (Latinised name Cartesius) (31.03.1596-11.02.1650) was a French philosopher, physicist, mathematician and physiologist. He was born in the small town of La Haye. He graduated from the Jesuit college of La Flèche (Anjou), was a soldier for a time and travelled. In 1628—49 he lived in Holland, and in 1649 he moved to Stockholm, where he died.
His research in physics was chiefly in mechanics, optics and the structure of the Universe. He introduced the concept of the “force” (measure) of motion (momentum), meaning by it the product of the “magnitude” of a body (its mass) and the absolute value of its velocity, and formulated the law of the conservation of motion (momentum), although he interpreted it wrongly, not taking into account that momentum is a vector quantity (1644). He also studied the laws of impact and was the first to formulate the law of inertia clearly (1644). He suggested that atmospheric pressure decreases as the altitude increases. With the publication in 1637 of the “Dioptrics”, which contained the laws of the propagation, the reflection and the refraction of light, the idea of the ether as the carrier of light and an explanation of the rainbow, he founded optics as a science. He was the first to derive the law of the refraction of light mathematically (this law was established experimentally about 1621 by W. Snellius). He gave a theory of magnetism.
He was the founder of Cartesianism and sought to construct a general picture of nature in which all physical and other phenomena would be explained as the result of the motion of large and small particles formed out of a single matter. Having no sufficient experimental material to rely on, Descartes (and his followers) made excessive use of hypothetical constructions. The main blow to Cartesian views was dealt by I. Newton.
In mathematics he was the first to introduce, in 1637, the concept of a variable quantity and of a function, and he laid the foundations of analytic geometry. In the theory of knowledge he was the founder of rationalism.