The water-filled glass barometer was invented in the 17th century and used to predict bad weather. It's also called a storm glass. The typical storm glass looks like an exaggerated teapot; it's a hollow glass globe or other rounded shape with a long spout attached. To set up the barometer, water is drawn into it in good weather. The air in the globe is effectively sealed off from the air outside by the water, so the air pressure within the globe stays constant. If the outside air pressure barometer changes drastically, the water level in the tube rises or falls.
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Things you need
- Two plastic dishpans
- Food colouring
Fill one dishpan with enough hot water to completely submerge the barometer. Don't make it too hot; you'll be putting your hands into it.
Fill the other dishpan with the same amount of cold water.
Submerge the barometer in the hot water. Hold it there until bubbles are no longer coming out.
Seal off the spout with your finger and move the barometer to the cold water. Release your finger from the spout. Water will then be drawn into the barometer from the spout.
Repeat these steps until there is enough water in the barometer to make the spout fill up halfway with water.
Remove the barometer from the water and dry it off. Add several drops of food colouring and move the barometer around gently to mix in the colouring.
Tips and warnings
- For best results, make sure you fill your barometer on a day when the local barometric pressure is 30 or above.
- Don't put your barometer on furniture that can be damaged by water; during extreme weather changes the water may spill out of the spout.
- The water barometer is sensitive to changes in temperature as well as air pressure; it works best when the temperature doesn't change much. So its accuracy is limited to situations where there are large pressure changes such as when a strong weather system passes through.
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