“An easie way to procure Fire speedily. Take a round Glasse, and fill it with faire Water, and set it against the Sunne, so that it may stand fast: then take something that is very dry, and hold it neere the Glasse, (betweene the glasse and the Sun) and it will set the thing so holden on fire: (which is very strange to behold), the rather because fire which is an hot and dry Element, is procured out of water, which is a colde and moist Element.”
The Booke of Pretty Conceits
This is a great trick if you can get the angle just right. If not, though, you’ll still end up with a nice glass of lukewarm water. Win!
How to Put Out a Fire, twelfth century, here.