Marc' Antonio De Dominis, a theologian and natural philosopher, born in Arbe, an island of Dalmatia, in 1566, died in Rome in September, 1624. He was a relative of Pope Gregory X., studied at Loretto under the direction of the Jesuits, and became a member of their order. He taught mathematics and philosophy with great success in several cities of Italy. In 1602 he left the Jesuits, and was appointed archbishop of Spalato and primate of Dalmatia and Croatia. He now began to oppose some of the measures of the court of Rome, and his writings were condemned by the inquisition. This gained him the sympathies of Protestants, by whom he was induced in 1616 to pass into England, where he embraced Protestantism, and was made dean of Windsor. Though his avowed aim was to effect a reunion of the two great divisions of Christendom, he wrote and preached against the papacy. In his work De Republica Ecclesiastica, he maintained that the pope is only prim us inter pares; it was censured by the theological faculty of Paris, and burned by order of the inquisition. Not long after its publication he reverted to his former theological views, publicly retracted all that he had ever written against the Roman Catholic church, and repairing to Rome abjured his apostasy.

His inconstant humor did not long leave him in repose, and it was suspected that he had repented his last conversion, and was meditating a return to Protestantism. He was imprisoned by Pope Urban VIII., and his sudden death soon after caused the report that he was poisoned. His trial for heresy was continued after his death; he was convicted, and his body was disinterred and burned along with his writings. His chief philosophical work is entitled De Radiis Visus et Lucis (Venice, 1611), to which Newton ascribes the first true explanation of the rainbow.