Before the Laboratory: Nine Scientists Who Taught the World How to Know

In the fifth century BCE Hippocrates taught on the island of Kos that disease has natural, bodily causes found by observing the patient, not the will of the gods. The Hippocratic Corpus records case histories that track symptoms day by day. Little is reliably known of his own life, so read the method as the lasting contribution.

Around 300 BCE Euclid wrote the Elements, thirteen books that derive ancient geometry from five postulates and a few common notions through explicit proof. His lasting gift was a standard of rigor: state your assumptions plainly and derive the rest, rather than appeal to authority.

Zhang Heng, a Han dynasty court astronomer, catalogued roughly 2,500 stars and built a water powered armillary sphere to track them. In 132 CE his bronze seismoscope, ringed with eight dragon heads, dropped a ball to show the direction of a distant earthquake that no one nearby had felt.

Hypatia led the Neoplatonist school in Alexandria and edited Diophantus's Arithmetica and Ptolemy's Almagest, passing mathematics and astronomy to students across the Roman world. No text in her own hand survives, so what we know of her work comes through her students and later commentary. She was murdered in March 415.

In 499 CE Aryabhata wrote the Aryabhatiya, which used a place value number system and gave pi to five significant figures. He stated that Earth rotates on its axis and explained eclipses as the shadows of the Earth and Moon, a physical account in place of omens.

Working at the House of Wisdom in Baghdad, al-Khwarizmi completed between 813 and 833 a book on al-jabr wa'l-muqabala that gave algebra its name and its first systematic treatment of linear and quadratic equations. His arithmetic treatise carried the Hindu-Arabic numerals westward, and his Latinized name, Algoritmi, is the root of the word algorithm.

In his Book of Optics, written around 1011 to 1021, Ibn al-Haytham argued that sight comes from light entering the eye, overturning the ancient idea of rays sent out from it. He made the case through controlled experiment and mathematical reasoning, which historians credit as an early form of the experimental method.

Al-Biruni, working at the Ghazni court, calculated the radius of the Earth to within about one percent of the modern value from the angle of dip to the horizon seen from a mountain of known height. It took trigonometry and one careful observation, not an expedition. He also studied Indian belief directly from Sanskrit texts.

Ibn Sina, known in Europe as Avicenna, wrote The Canon of Medicine around 1025. It set rules for testing a drug: try it on an uncomplicated case, see the same result across repeated trials, and rule out other causes. European universities used it as a standard textbook into the seventeenth century.