Salem Clock Shop - 1085 Broadway Street NE, Salem, OR 97301 - (503) 581-3803 Fax: (503) 581-3331
You can build a homemade bottle barometer and use it to help make accurate local weather forecasts.
Weather Glass Barometer
If you are constructing one of these during a spell of bad weather, you will have to wait until the weather improves to see how the barometer acts. Rising atmospheric pressure as a high moves in will press with more force on the surface of the water and push the column of water in the bottle to a higher level.
Clear glass jar (approx. 18 ounces)
straight-neck glass bottle (approx. 12 ounces)
Find a bottle with a straight neck and a jar that is tall enough for the bottle to sit in upside down without having the neck touch the jar's bottom. Also, the bottle must not fit so tightly as to form an air-tight seal. One combination that has been suggested is a Star brand white vinegar bottle and an 18-oz. peanut butter jar. Remove all labels, clean the bottle and jar, and invert the bottle into the jar.
Fill the jar with enough water to come up just over the mouth of the bottle by an inch or a little more. Add a few drops of food coloring. Tip the bottle and jar enough to let a little air escape from the bottle so that the liquid is now up in the neck of the bottle and level with the water in the jar.
Slide the rubber band onto the outside of the jar and position it at the same level as the water. Set the barometer in a spot out of direct sunlight, where it can be observed but won't get knocked over. As the water rises and falls in the neck of the bottle, use the rubber band to mark the new level.
To show other people how the barometer works, there is this demonstration; find a pot or dishpan in your kitchen and fill it with water. Ask those interested to press down on the surface of the water with their hands, to see how the level of the water rises and then falls when they press down or let up. Explain that the air around them presses against everything and likewise presses down on the water in the jar, forcing the water up the neck of the bottle when atmospheric air pressure rises. Below is a simple diagram of the basic forces involved.