Commentary on Archibald Pitcairne's Edinburgh edition of Solutio Problematis de Historicis; seu de Inventoribus Dissertatio, (1688) of which an enlarged edition appeared at Leiden in 1693. This tract made Pitcairne's subsequent medical career on the continent for its vindication of the claims of William Harvey to the discovery of the circulation of the blood. It contains other things as well, notably the first public presentation of Gregory's second method of quadrature, on which Pitcairne and Gregory worked together between 1685 and 1691 when Gregory moved to Oxford. Pitcairne, who hailed from Edinburgh, was an enthusiastic amateur mathematician, and in fact helped secure Gregory's appointment as professor there.