(1711-1787) Natural philosopher, born Ragusa, Italy; died Milan, Italy. Educated at the Jesuit college at Ragusa, he joined the order and was appointed professor of mathematics at the Roman College, 1740. Besides publishing astronomical dissertations on sunspots, transit of Mercury, etc., he showed his ability as a practical engineer by repairing the cracked dome of Saint Peter's, measuring an arc of a meridian between Rome and Rimini, and making a complete survey and map of the States of the Church. He invented a micrometer, still used, which requires no artificial illumination of the field of the telescope. In his work on the molecular theory of matter he holds that all matter consists of innumerable point-like structures which repel each other when they are very close; as their distance increases the repulsion becomes attraction. He headed a political embassy which resulted in his being elected a Fellow of the Royal Society of London.