The Harbottle helps students to understand the meaning of fluid pressure and pressure reduction. Simply place a balloon into the opening of the glass Harbottle and stretch the mouth of the balloon over the mouth of the bottle. Blow into the balloon and, when it is fully inflated, stopper the bottom hole of the Harbottle. The balloon will stay inflated even though it is open to the atmosphere. Excellent teaching tool for discussion on pressure, vacuum, pumps, and weather. Includes Harbottle, balloon, rubber stopper, and complete included.