How to Test Barometric Pressure With a Bottle Half-Full of Water

You can make a homemade water glass to measure barometric pressure.

Barometers are weather instruments that respond to changes in atmospheric pressure (air pressure). They help predict the weather. The original 1643 barometer used a column of mercury that rose or fell to measure air pressure. The weather glass, also called a storm glass or Goethe's barometer, was developed at about the same time. A simpler and less expensive instrument, the water glass, was used by individuals such as farmers and sailors, who needed to know what the weather was going to do. Water glasses often resemble tea pots, but may appear as swans or other decorative shapes.

Things You'll Need

• Clear glass bottle with a narrow neck
• Rubber stopper to fit the neck of the bottle
• Drill
• Rigid, clear plastic tubing, about twice the height of the bottle
• Extra fine-tip permanent black marker
• Ruler
• Clear silicone sealant
• Food coloring (optional)

Instructions

1. Check the weather report. Find a day of average air pressure to construct the barometer to allow the water enough room to rise and fall in response to pressure changes.

2. Bore a hole, the diameter of the plastic tubing, through the stopper from top to bottom. Aim for a snug fit. Cork is not a suitable material for the stopper because it allows some air to pass through.

3. Fill the bottle halfway with water. Add drops of food coloring, if desired, until you obtain the color you want. The coloring is decorative, and will not affect the functioning of the barometer, although it will make the readings simpler to see.

4. Push the plastic tubing through the hole in the stopper. Insert the stopper into the mouth of the bottle. The bottom end of the tubing must be about two inches below the water level.

5. Mark a measuring scale on the plastic tubing above the stopper, so you can track changes in the water level.

6. Blow some bubbles into the water, through the plastic tubing, to increase the air pressure inside the bottle. This forces the water to rise up the tubing. When you take your mouth off the tubing, water will rise up the tube past the rubber stopper. If it does not, check for air leak and try again.

7. Seal with the silicone where the tubing meets the stopper and where the stopper meets the mouth of the bottle

8. Allow the barometer to stabilize. Observe and record the initial barometer reading. Changes in the readings mean a change in weather. Rising air pressure causes the water level to fall, indicating clear weather. Falling air pressure causes the water level to rise, indicating precipitation, or stormy weather. This is opposite a homemade mercury barometer. Steady readings mean the weather will hold.

References

• NASA: It's a Breeze, How Air Pressure Affects You
• Home Weather Stations Guide: Ever Wanted to Make Your Own Barometer?
• Home Weather Stations Guide: The Weather Glass, The Farmer's and Sailor's Barometer