Dyes, Planets, and Peas

Editor's Note: Today we revisit three ScienceThens, first posted last year.

A Discovery to Dye For

Tuesday, 24 February: Today is the birthday of Carl Graebe, a German organic chemist born in 1841 whose work helped create the synthetic dye industry. Graebe and co-worker C. Liebermann discovered that a red dye called alizarin--then made from madder, a Eurasian herb--was a derivative of anthracene, a crystalline cyclic hydrocarbon. The duo built on the discovery to invent a commercial method of synthesizing alizarin, which became one of the early products of the German dyestuffs industry. Graebe also introduced the chemical terms "ortho," "meta," and "para," well known to organic chemistry students, which indicate the position of groups attached to a benzene ring.

Discoveries by Induction

Thursday, 26 February: Today is the birthday of Dominique François Jean Arago, a French astronomer and physicist born in 1786. Arago is best known for his discovery of the chromosphere--the sun's lower atmosphere--which is composed primarily of hydrogen gas, and for his accurate estimates of the diameters of the planets. In physics, Arago found that a rotating copper disk deflects a magnetic needle held above it, a phenomenon later explained in terms of magnetic induction. He also showed that light waves move more slowly through a dense medium than through air. Arago entered politics in 1848 as Minister of War and Marine and was responsible for abolishing slavery in the French colonies.

Revealing Our Genetic Heritage

Saturday, 28 February: On this day in 1865, Austrian monk Gregor Johann Mendel presented seminal results of his plant-breeding experiments at a meeting of the National Sciences Society in Brno, Czechoslovakia. Although Mendel's work passed unnoticed for decades, it became the basis for the science of genetics. After 8 years of cultivating some 28,000 pea plants and analyzing seven pairs of seed and plant traits, Mendel uncovered the fundamentals of heredity, including the concepts of dominant and recessive traits, and recombination. Mendel was a pioneer in using statistical analysis of large sets of numbers to extract laws of nature from seemingly random phenomena.

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