This may be apocryphal, but I've heard that the reason Galileo invented the telescope wasn't to look at the stars, but rather to look into the future. Supposedly he'd stand in the St. Mark's Sq. Bell Tower watching for foreign ships, and then use this information to arbitrage commodities.
The seas around Venice are all shoals with just a few approaches. And the air is pretty hazy. I think small boats would bring news of approaching ships before anyone could see them from St Mark's.
Apparently Galileo did demonstrate his telescope from the top of St Mark's, showing some Venetian senators that with it they could see the sails of distant ships. For that information to be valuable, though, it would have to be the first news to be had of them, and that seems unlikely.
