A simple mercury barometer

Seal single end of a glass tube about 80 cm in length by rotating it in a gas flame. The tube should be held as almost vertical as possible. Join a small funnel or thistle tube to the open end of your barometer tube with a short length of rubber tube. Pour mercury into the tube gradually. If air bubbles are trapped they may be separated by gently shaking the mercury in the tube up and down. Fill the tube to within 1 cm of the top. The last part is best filled by using a medicine dropper so that mercury will not be exhausted. Fill the tube until a little mercury extends above the tube level. Pour about two centimetres of mercury into a bottle or dish. Place your handle over the end of the tube and place the tube open end down in the jar of mercury. Take away the finger from the tube when it is under the surface of the mercury. When this tube is properly support it will serve as a mercury barometer. The height of the mercury among the levels in the jar and the tube calculates the air pressure in centimetres or inch of mercury.