Seamen's and scientists' tides. How the practical knowledge of tides was used in the 16th century natural philosophy. Case study on Nicolo Sagri and Francesco Patrizi of Cherso.

The debate on the causes of the tides was very lively in the late 16th century within learned circles. But althought the interest in tidal theories was high, the tidal data that was then available and quite accurate, was seldom used in theoretical contexts. A notable exception in this was Italian renaissance philosopher Francesco Patrizi, who systematically and with a good profit used the tidal data presented by Nicolo Sagri, Venetian master mariner.

The use of the Sagri's data made it possible for Patrizi to forcefully argument against then popular lunar theories of tides. Patrizi's arguments against lunar theories contained also some new ideas which stemmed from the tidal observations collected by Sagri.

Patrizi's use of Sagri's data in his "Nova de universis philosophia" (1591) proves that he saw this Italian mariner as a credible source of empirical information – this was against natural philosophy's tradition, which preferred classical writers for empirical data or examples. The reason why Patrizi trusted in Sagri requires then an explanation. My argument is that Sagri's way to provide the tidal data – it was systematic, comprehensive and specific – is the key here. Another reason might be that Patrizi in his younghood became to know Venetian mariners' practices and probably also the portolan books, or coastal sailing guides, which were Sagri's primary source of information when he wrote his ”Ragionamenti sulla varietà dei flussi del mare Oceano Occidentale” (1574). It is noteworthy that Patrizi does not even mention Sagri's tidal theory. In this Patrizi can be seen as an orthodox natural philosopher; to him it was still and only the scientist who had an access or a capability to the causes of the natural phenomena.