Joseph Proust

Joseph Louis Proust was born in France on 26 September 1754. Working as a chemist through the turn of the 19th century, he arrived at a discovery that redrew the ground rules: in 1797 he announced the law of definite proportions, the principle that chemical compounds always combine in constant, unchanging ratios. It was a line in the sand against randomness, proof that matter obeyed strict mathematical order. He died on 5 July 1826, leaving chemistry with a law it still teaches in every first-year course.