This machine was designed to harness steam power to project missiles from a cannon. No gunpowder was required.
The copper cannon on wheels could easily be moved over the battlefield. Once in place, the breech of the cannon is heated to a high temperature, water is poured into it, and the resulting steam pressure forces the cannon ball out of the barrel. There would have been a loud explosion, with great clouds of steam.
The idea was inspired from the works of Greek mathematician Archimedes.