Start with the upper flask mostly full and the lower flask empty. Pour 50 ml of water into the fountain dish to prime. As the water falls from the fountain dish to the lower flask, air pressure in the lower flask increases. The lower flask is connected to the upper flask by an air tube, increasing the pressure in the upper flask. This pressure forces water from the upper flask up to the fountain.
Fountain height is comparable to the distance of separation between the two flasks. This process will continue until the upper flask is empty. To reset, transfer the water from the lower flask to the upper flask, leaving out 50 ml to prime the fountain.