Not only the triangular, but also the quadrilateral version were known, used for centuries (mostly on smaller craft) in parallel with square sails.

I'm taking the temperature of the canal outside, pumping it through the heat exchange mechanism, it's turning through these amazing sails on the roof, and that, in turn, is falling softly onto the people in the restaurant, cooling them, or heating them, as the need may be.

And with the same dogged determination that my father had bred into me since I was such a child he taught me how to sail, knowing I could never see where I was going, I could never see the shore, and I couldn't see the sails, and I couldn't see the destination.

For almost three decades, John Francis has been a planetwalker, traveling the globe by foot and sail with a message of environmental respect and responsibility . A funny, thoughtful talk with occasional banjo.