A golf ball cannon is an object that is closely related to the spud gun, potato gun and tennis ball cannon. It uses a propellant such as hair spray, compressed air, or acetylene.
The difference between a golf-ball cannon and a spud gun is that it is an automatic weapon. It uses gravity and the explosive force of each shot to launch the golf ball a great distance. The gas flow into the resevoir is continuous normally, and the impact of a falling golf-ball causes the gas-flow to cut, and fires up an igniter. The ignition re-opens the gas flow and causes a new golf ball to drop. I'm very bad at ascii art, so I won't include a diagram.
As far as I know, these guns only exist in the Detour area of Carroll County, Maryland. Two of them are truck-mounted, so if you want to see one just look for the '79 Ford Ranger that looks like it came out of a Mad Max movie.