Francois Arago. Engraving of Dominique Francois Jean Arago (1786-1853), French physicist and astronomer. Arago showed that metals other than iron could have magnetic properties; he also disc- overed that an electric current produces a magnetic field. In 1838 he devised an experiment to prove the wave nature of light by comparing its speed in air and water; this was performed successfully by Foucault in 1850. Arago discovered the Sun's chromosphere, a layer of gas above its visible surface, in 1842. He also showed that comets reflected sunlight rather than producing their own. He entered politics and helped to abolish slavery in the French colonies in 1848.