Du quadrant vetustior à l’horologium viatorum d’Hermann de Reichenau : étude du manuscrit Vaticano, BAV Ott. lat. 1631, f. 16-17v

The fragment of a correspondence between two Latin scholars, kept in Vaticano, BAV Ott. lat. 1631, f. 16-17v, and the diagram reproducing a horary quadrant in London, BL Royal 15 B IX, f. 60v, prove that, about 1050, an Arabic instrument, unknown untilthen to the Latin scholars, was introduced into the Occident, probably at the same timeas the cylindrical sundial described in the De horologio viatorum. This quadrant, on which is drawn a horary diagram founded on a zodiacal scale, was imported after thevetustissimus quadransand before thevetus quadrans. We can suggest, in all probability, that the author of the letter, B, Berengarius, and his correspondent, W, Werinherus,were on familiar terms with Hermann the Lamer. Moreover, the fragment preserved in Vaticano, BAV Ott. lat. 1631, f. 16-17v, is an extract from a letter which, in the beginning, may have included the account about the horary quadrant, the diagram transcribed in London, BL Royal 15 B IX, f. 60v, and the De horologio viatorum. So Hermann the Lamer can’t be the author of the De horologio viatorum. Moreover, the letter of B is the source of the chapters De utilitatibus II, 6 and Geometria Incerti Auctoris III, 6. So the collections De utilitatibus II and Geometria Incerti Auctoris III (class D) came after the correspondence between B and W.