Bore a hole from the inside through the screw top of an aluminium pill tube about four inches long, and pour some water into the tube. Fix the tube in an empty sardine can into which you have fixed three candle stumps and place the can in water. If you light the candles the water soon boils, and the jet of steam escaping from the back drives the boat.Steam is formed in the boats boiler when the water boils. Because it expands sharply, it escapes at high pressure through the nozzle and causes a recoil. Do the experiment in calm weather!