Place the opening of the drum in front of the nozzle of the fog machine, and press the button on the control to fill the drum with fog. Aim the opening toward the class and upward, and give the rubber diaphragm a tap. A smoke ring will emerge from the opening. Such a smoke ring is shown above, at right. As long as there is still fog in the drum, whenever you tap, a smoke ring will emerge. These smoke rings typically travel 20 or 30 feet before they dissipate. A spotlight (not shown) allows you to illuminate the region through which you are sending the smoke rings, to make them easier to see.