A water barometer or storm glass is used to predict stormy weather. It works because of changes in atmospheric pressure. It is usually made with a glass container that has a sealed body and a narrow spout. The spout connects to the body below the water level, which should fill the body halfway. The top of the spout is above the water level and open. When air pressure sinks lower than when the body was sealed with water, the water level in the spout rises above the level in the body. This device can be filled using a combination of hot and cold water, and is best to fill on a good day when the local pressure reads 30 and above.
Submerse the barometer completely in the hot water until bubbles stop coming out of the spout.
Place a finger over the spout and move the barometer to the cold water.
Remove your finger to let the cold water be drawn into the spout.
Repeat Steps 1 through 3 until the water is about half an inch above the top of where the spout enters the bottle.
Let the water reach room temperature. This will take about an hour.
Tip the barometer over and let about half the water in the spout pour out.
Add food colouring through the spout, if desired.