The Harbottle is a spherical glass container with a balloon stretched over its opening and a hole in the flattened base that is fitted with a rubber stopper.

See students be amazed when they observe that the balloon remains inflated inside the bottle even though it is not tied off or sealed.

Or fill the inflated balloon with water before removing the rubber stopper.

An excellent tool to introduce pressure to students and its applications to real life equipment (e.g. vacuum cleaners, pumps) and phenomena (flight, weather).