- Nationality
- Flemish
- Gender
- Male
- Occupation
- mathematician and engineer

Simon Stevin was born in Bruges, Flanders, the son of Antheunis Stevin and Cathelijne van de Poort. As a young man, he began work as a bookkeeper, but soon found work as an itinerant engineer. He traveled widely, visiting France, Germany, and perhaps even Poland and Norway before returning to Bruges in 1577to become a tax collector.

In 1581 Stevin traveled north to enter the University of Leiden, where the first classes for engineers were being held. The works of antiquity had been newly rediscovered, and those of Euclid, Apollonius of Perga, and Archimedes would play a large part in Stevin's own scientific accomplishments. (Stevin added to this cultural revival by translating the works of Diophantus of Alexandria for the first time.)

Stevin is best known as a contributor to two branches of physics: *statics* (the science of forces producing equilibrium) and *hydrostatics*.

Stevin, like René Descartes and Galileo, wrote almost all his works inthe vernacular, marking the decline of Latin as the European scholarly language. He considered Dutch perfect for scientific discourse, and he coined manynew terms which survive in that language today.

A true Renaissance man, Stevin published books on a variety of scientific andhumanistic topics, but devoted most of his studies to mathematics and engineering. His works are characterized by his uncommon skill in combining theoryand practice, and his uncanny ability to foreshadow later discoveries. They reflect the contemporary belief in the prevalence of reason, and the ultimatecomprehensibility of nature.

His first publication, *Tafelen van interest* (Tables of interest) (1582), listed rules for computing interest and tables for calculating discounts and annuities. This information had been closely guarded by banks, primarily because there were few people with the skill to perform such computations, butperhaps it preserved a financial advantage as well. After Stevin's work waspublished, interest tables were available to anyone who could read.

Stevin's principal work in statics is *De Beghinselen der weeghconst*, published in 1586. In it, Stevin described his most famous discovery, the *law of inclined planes*, which he proved by drawing an imaginary circle ofconnected, equal weights called a *clootcrans*, or wreath of spheres. The basic premise of the law is that less weight on a steep slope can balance more weight on a gentler slope. Stevin was so delighted with his find that beneath the illustration he wrote *Wonder en is gheen wonder*--" what seemsmysterious can be understood". The phrase became his motto, and the seal, appearing on his letters, his instruments, and the title pages of his books.

Stevin's other famous publication, *De Beghinselen des waterwichts*, wasthe first since antiquity to study Archimedes's principle of displacement. Stevin added many new ideas of his own, including one that is the fundamentalprinciple of hydraulics: the pressure exerted by a liquid depends only on itsheight, and not on the shape of its container. This meant that a small amount of fluid could produce a large amount of pressure if it were held in a long, narrow tube.

In another branch of science, Stevin was upstaged by his contemporary Galileo. Although credit has historically been given to the Italian, it was Stevin who first refuted Aristotle 's mistaken belief that heavier bodies fall fasterthat light ones. He dropped two lead balls, one 10 times heavier than the other, from a height of 30 feet and found that they hit the ground simultaneously. He published his findings years before Galileo, but never attained the same degree of fame.

In *De thiende *(The tenth) and De disme (The decimal), both published in 1585, Stevin discussed decimal fractions and described their usefulness ineveryday life. Until this time, decimals had been used only in the rarefied realm of trigonometry, and then only occasionally. Although awkward by modernstandards, Stevin's notation was a vast improvement over sixteenth-century methods, and decimal fractions were soon in wide use.

Stevin parted company with his fellow mathematicians on a few points. He believed, for example, that all numbers, even irrational or imaginary numbers, were basically alike, a view not widely held until the development of algebra.He also challenged the centuries-old Greek method of mathematical proof, *reductio ad absurdum*. He introduced a different means, which, although unwieldy, hinted at improvements made later in calculus. Neither was he afraid of controversy. In *De Hemelloop* (1608), an astronomical treatise, Stevin explained and supported the Copernican theory, in which the Earth and otherplanets orbit the sun. This book was published several years before Galileo's famous clash with the pope over the same topic, and predated most other scientists' acceptance of a sun-centered cosmos.

Stevin also proposed a decimal system for weights, measures, and currency, ideas that were not adopted until hundreds of years later. The true inventor ofdecimal notation is not known, although the idea may have originated in China or India. It is known that the fifteenth-century Arabic mathematician Muhammad al-Qushchi (died c. 1430) used decimals to calculate the value of pi to 16 places. In Europe, C. Rudolff (fl. 1500s) described decimal notation and its manipulation 50 years before Stevin advocated its general use.

Stevin was a practical man, and he brought his engineering skills to the burgeoning commercial and industrial world of the Netherlands. He was a prolificinventor, solving problems wherever he found them. Perhaps his best-known achievement was a system of sluices and locks that used tides to flush canals; the valves could also be opened to flood the country in case of an invasion. He invented a winch to lift boats out of the water, and a mechanical spit foruse in cooking. A rather whimsical design published in 1599 describes a 26-passenger sail-propelled carriage that was intended for use along the seashore.Stevin also patented embanking and drainage inventions (a constant priorityin the waterlogged Dutch countryside), including notable improvements in windmill design. Using mathematics, Stevin analyzed both the scoop wheels that mills used to remove water and the gears that drove them. In *Van de Molens* (About windmills), he proposed slowing the wheels' revolution and changingthe gears' construction to engage the teeth on the face, not the rim. Several mills were altered to these new specifications; unfortunately, technology sorely lagged behind theory, and the craftsmen of the day were not able to execute Stevin's design as perfectly as he envisioned it.

Stevin eventually entered the service of Prince Maurice of Orange, who commanded the Dutch army in the country's struggle for independence from Spain. Stevin served as the Prince's tutor and as a trusted consultant on matters of defense and navigation. He became the army's Quartermaster-General in 1604, responsible for providing accommodations for the troops. Stevin's military experiences influenced his later inventions, although his ideas on the art of fortification, too expensive for their time, were used successfully by armies a century later. They did have one practical expression--a combination pick, shovel, and axe that Stevin devised for use in building fortifications.

In his later years, Stevin organized a school for engineers at Leiden. He settled down with a young woman named Catherine Cray, by whom he had four children. One of them, his son Hendrick, became a scientist in his own right.

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