Today I have been working on a model of a Hero's Aeolipile. I found half a dozen of these bronze hemispheres as garden ornaments in my grandparents garden...they were promptly requisitioned for use the basis of a model of Hero's Aeolipile.
For those who don't know, the Aeolipile was an invention of Hero of Alexandria in the 1st Century AD. and is supposed to be the first steam engine ever. It comprises of a copper cauldron on-top of a fire, the steam produced is fed into the ball and is ejected pipes in the side, causing it to rotate. See this Wikipedia page for more information.