This activity has a slightly deferred payoff: The kids have to wait until the weather improves to see what the barometer does. The day after we set up ours, a sunny day following protracted bad weather, the girls came to breakfast and shrieked for me to come see the column of blue water in the neck of the bottle, an apparent contradiction of everything they have ever understood about gravity.

MATERIALS:
• Clear, straight-neck glass bottle (about 12 oz.)
• Clear glass jar (about 18 oz.)
• Food coloring
• Rubber band

STEP 1
Find a bottle with a straight neck and a jar that's tall enough for the bottle to sit in it upside down, without the neck touching the jar's bottom. One combination that works beautifully 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.

STEP 2
Fill the jar with enough water to come up just over the mouth of the bottle by an inch or so. Add a few drops of food coloring and tip the bottle and jar enough to let a few air bubbles escape from the bottle.

STEP 3
Slide the rubber band onto 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 by the kids 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.

STEP 4
To show your kids how the barometer works, try this demonstration: Take a large pot from your cupboard and fill it halfway with water. Ask your kids 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 let up. Explain that the air around them pushes against everything and presses down on the water in the jar, forcing the water up the mouth of the bottle. High pressure means air is pressed down toward the earth, where it warms up and stays clear, while low pressure lets air rise and cool, making the clouds that lead to rain.