This experiment has a drop of oil suspended in a capilliary tube that is open at the top end to the atmosphere keeping a constant pressure on the air below the drop. The water starts off hot and cools over time. It can be cooled quicker by adding cold water from the tap. The water needs to be stirred to maintain a constant temperature. The student takes readings of the length of the column of air beneath the oil drop (giving the volume of air) and the temperature using the digital thermometer.