Arago, Francois Jean Dominique, an illustrious French physicist, born in 1786. Entering the Ecole Polytechnique at the age of 17, he was three years later appointed assistant to Biot for the purpose of verifying the measurement of the earth. In 1809 he received a professorship in his former school, became director of the Observatory, and in 1830 was elected perpetual secretary of the Academy of Sciences. From 1831 to 1848 he took an active interest in politics as a moderate but earnest Republican, and in the latter year was appointed a member of the Provisional Government, and marched with the troops against the barricades, after which he retired in disgust from public affairs. Arago's contributions to science were varied and brilliant. He finally established the undulatory theory of light; extended our knowledge of the phenomena of polarisation; advanced considerably the researches of Oersted and Ampere into the relations between magnetism and electricity; discovered rotary magnetism, for which he was awarded the Copley medal of the British Royal Society, and introduced many improvements in the construction of astronomical instruments. His skill in popularising scientific ideas was almost unrivalled. Strangely enough, he left behind him no great literary record of his achievements, though he contributed freely to the learned periodicals of his day, and founded, with Gay-Lussac, the Annales de Physique et de Chimie. Arago refused to recognise the government established by the Coup d'Etat of 1852, and Louis Napoleon honourably respected his consistency. Broken in health, he went to his native Pyrenees in the vain hope of recovery, but returning to Paris, died in 1853 and received a public funeral.