This is bothering me way more than it should. Ever since I saw the following image: http://i.imgur.com/iUZsw3Cl.jpg?1 (This is a fraction of a set of pictures that contains other cool people with quotes that would be considered "ignorant" nowadays. All credit goes to the original author. I have no proof that the quotes are correct. Be aware that in the internet anything a person has ever said can be turned into something else and/or attributed to anyone. Original set of images) I've been wanting to come with a theoretical model to make it work. But I don't know what concepts of physics would be used to explain it. Of course nowadays I would go with electricity and it would be so easy. But assuming I'm living in those times and there are no turbines, no engines, or electricity how would I make a ship which in theory can move against the wind and currents by using fire? How does one harness the power of fire for this purpose? This is an old problem, and in this forum it may not be constructive at all because there are better solutions today. Still, I'm curious. It would be fun to understand.