(2) The notion that the Sun exerted some centripetal force on the planets was now becoming pretty well accepted, but by asking for data on the interactions of moon and sea, and of Jupiter and Saturn, Isaac was as much as saying that these were all of a piece, that everything attracted everything – that the influences on (say) Saturn of the Sun, of Jupiter, and of Titan (the moon of Saturn that Huygens had discovered) were different only insofar as they came from different directions and had different magnitudes. Like the diverse goods piled up in some Amsterdam merchant's warehouse, they might come from many places and have different values, but in the end all that mattered was how much gold they could fetch on the Damplatz. The gold that paid for a pound of Malabar pepper was melted and fused with the gold that paid for a boat-load of North Sea herring, and all of it was simply gold, bearing no trace or smell of the fish or the spice that had fetched it. In the case of Cœlestial Dynamics, the gold – the universal medium of exchange, to which everything was reduced – was force. The force exerted on Saturn by the Sun was no different from that exerted by Titan. In the end, the two forces were added together to make a vector, a combined resultant force bearing no trace of its origins. It was a powerful kind of alchemy because it took the motions of heavenly bodies down from inaccessible realms and brought them within reach of men who had mastered the occult arts of geometry and algebra. Powers and mysteries that had been the exclusive province of Gods, Isaac was now arrogating to himself.