Peregrinus, Petrus (Peter the Pilgrim)pēˈtrəs pĕrəgrĭnˈəs, c.1220–?, medieval scholar and soldier. The tutor of Roger Bacon, he wrote the first important study of magnetism, Epistola de Magnete, in which he described simple magnetic attraction and repulsion. He improved the compass by placing the lodestone on a pivot and surrounding it with a graduated directional scale. His ideas were further elaborated in the 16th cent. by William Gilbert.