Materials Needed:

-Drinking straw (clear plastic)

-Narrow-neck glass bottle

-A rubber or cork stopper which fits in the neck of the bottle Instructions

1. Insert a drinking straw into the bottle.

2. Fill the bottle about half-way full of water.

3. Seal the neck of the bottle around the straw either with the rubber stopper or a cork.

4. Make sure the end of the straw is immersed in the water and that the water level in the straw is above the top of the bottle.

As the air pressure outside the bottle decreases, the trapped air inside the bottle will push the water up the straw. As the air pressure outside the bottle increases, it will push the water farther down the straw.

Please Note: You'll need to keep your barometer's temperature constant, since temperature will also affect the water level.