Paper, 'On calculating longitudes' by Henry Oldenburg Henry Oldenburg here comments on someone else's suggestions for calculating longitude on the basis of the sun and a star. Although the text mentions the Italian astronomer Giovanni Battista Riccioli (1598-1671), Oldenburg seems to imply that he is not directly commenting on his book 'Geographiae et hydrographiae reformatae' [Reformed geography and hydrography] (Bologna, 1661). Includes two geometrical diagrams in the text. Subject: Astronomy / Navigation [c17th Century]