Nicole Oresme

France
1320-1382
Philosopher, economist, mathematician, and physicist, one of the principal founders of modern science and one of the most original thinkers of the 14th century. By the age of 36,  he was grand master of the Collège de Navarre and  canon of Rouen. On 3 August 1377 he became Bishop of Lisieux.

In his mathematical work, Oresme developed the notion of incommensurate fractions, fractions that could not be expressed as powers of one another, and made probabilistic, statistical arguments as to their relative frequency. He argued that the movement of planets and stars were similarly incommensurate, and astrology was therefore a hoax.

In order to describe the motion of objects, Oresme invented the 3-D rectangular co-ordinate system. He proved this system equivalent to an algebraical relation in which the longitudes and latitudes of any three points combine: i.e., he gives the equation of the right line, and thus anticipated Descartes in the invention of analytical geometry.  Oresme’s mathematical demonstration of motion within this system is exactly the same as the system Galileo used in the seventeenth century. In fact, Oresme’s system was still being taught at Oxford by William Heytesbury and his followers, then, at Paris and in Italy, during Galileo’s lifetime. In the middle of the sixteenth century, long before Galileo, the Dominican Dominic Soto applied the law to the uniformly accelerated falling of heavy bodies and to the uniformly decreasing ascension of projectiles.
Oresme’s teachings on statics and dynamics follows the opinions advocated in Paris by his predecessor, Jean Buridan de Béthune, and his contemporary, Albert de Saxe. Oresme brilliantly argues against any proof of the Aristotelian theory of a stationary Earth and a rotating sphere of the fixed stars. The whole of his argument in favour of the earth’s rotational motion is both more explicit and much clearer than that given by Copernicus. Significantly, Oresme developed the first proof of the divergence of the harmonic series, something that was only replicated in later centuries by the Bernoulli brothers. He also worked on fractional powers, and the notion of probability over infinite sequences, ideas which would not be further developed for the next three and five centuries, respectively.

Oresme is generally considered the greatest  of medieval economists. He presented his economic ideas in De origine, natura, jure et mutationibus monetarum, the first comprehensive work upon money. Oresme argued that coinage belongs to the public, not to the prince, who has no right to arbitrarily change the content or weight of coins. His description of the destructive effects of debasing a nation’s currency clearly and incisively influenced Charles V’s monetary and tax policies. Oresme also pointed out that in a society in which two currencies with the same designation but of different value circulate, the money of lower value drives out the money of higher value. Nicolaus Copernicus (1473–1543) independently described this in his own commentary on the reform of the Prussian coinage, as did Thomas Gresham (1519–1597). Today it is called Gresham’s Law.