Building a balloon barometer is pretty simple all you need is a wide mouth jar, a large balloon, a broom straw or pipe cleaner, glue, a rubber band, a smear of butter. Smear the butter around the rim of the jar, it helps create the airtight closure. Cut the neck off the balloon then stretch the belly of the balloon tight across the jar top and secure it with a rubber band. Make sure you have created an airtight closure around the rim and on the surface of the balloon. Now take the broom straw and glue it in the center of the rubber lid and on the very edge of the jar. The straw should extend at least 6 inches from the rim of the jar.
How It Works: As the weather patterns shift the air pressure around the jar changes but the air pressure in the jar remains the same. An increase in pressure outside pushes the balloon down forcing the end of the straw up While a decrease in pressure will cause the balloon to swell pushing the straw down.
Inspired from Cricket , the magazine for children Volume 3, number 2, October, 1975
(yes, I have a vintage collection of Cricket magazines!!! <3)