Lambert, Johann Heinrich
Mathematician, born in Mülhausen, Germany. Largely self-educated, he worked as a secretary and tutor, and in 1764 moved to Berlin, where Frederick the Great became his patron. He was among the first to appreciate the nature of the Milky Way, and in an inconclusive attempt to give a rigorous proof of Euclid's parallel postulate he established several theorems in non-Euclidean geometry. He also demonstrated that Pi is an irrational number (1768). The first to show how to measure scientifically the intensity of light (1760), the unit of light intensity is now named after him.