In the “Opus Tertium,” the last of the series of three which, it is said, were all completed in about eighteen months, he speaks more than once of A.D. 1267 as being the then current year. This happens to be but two years prior to the date of the epistle of Pierre Pélerin de Maricourt, the great experimentalist (Petrus Peregrinus), whom he commends (p. lxxv) in the following words: “For there are only two perfect mathematicians, Master John of London[16] and Master Peter of Maricourt, the Picard ... who is worth more than any of them ... of whom I have fully written in my ‘Opus Minus’ and of whom I shall write more in its proper place.” Of this Master Peter, whom he calls one of his most illustrious pupils, he further says that, being “struck with the genius that dawned in his countenance,” he took him under his protection from his fifteenth year and instructed him so carefully that he outstripped all of his contemporaries both at Oxford and at Paris. “There is no one,” adds he, “who knows so much of the root of Philosophy ...” and one who, “through experiment, gains such knowledge of things natural, medical, chemical; indeed, of everything in the heavens or earth.” Gilbert states (“De Magnete,” Book I. chap. i.) that many believe the work of Peter Peregrinus on the magnet owes its origin to the opinions of Roger Bacon. And in the Appendix I to Brewer’s work--p. 537, chap. vi. “De Experimentis Mirabilibus”--will be found Bacon’s views fully exposed on the operations of the magnet.