Find hollow glass flowers or watering bulbs. If the glass is completely sealed, break the stem so you can pour water in. Fill the hollow glass partially with water and invert its mouth into a planter that is filled with water. Don't rest the stem on the bottom of the bowl but leave it suspended. When you do this, you want the water level to be halfway up the stem, so you may have to fill and invert the flower a few times before the water level is right. Wrap fishing line around the head of flower. Tie the other end of the fishing line around a screw's head and screw it into the ceiling. As the air pressure fluctuates, the water will move up and down in the stem of your glass flower. Do this with several flowers and to make a barometer garden.
Find an old oil tin circular screw top and clean it with degreaser and water. Measure the diameter of the oil can's opening and get a rubber stopper that will fill the opening. Drill a hole through the center of the rubber stopper and run a glass straw through the stopper. Since glass straws are easy to break, protect your hand with a towel and dab a small amount of lubricant onto the glass straw so it will slip through the hole easily. Dye water dark brown or black and fill the oil tin with it. Insert the stopper into the screw top, twisting it in. The glass straw should reach into the water. With your mouth blow air into the straw. The air pressure inside the bottle will increase and push water up the straw. Blow more air until the water is at the desired height. When the air pressure increase, the water level in the straw will fall, and when the air pressure decreases the water will rise.
Color a surgical glove so that it looks like a hand. Stretch the opening of a surgical glove around the mouth of a mason jar or coffee can. Wrap a rubber band around the glove just below the mouth of the jar so it holds the glove tight and forms an air-tight seal. Slip a drinking straw up under that seal and blow into the drinking straw until the glove is completely blown up. Quickly remove the straw. Tape something between its fingers, like cigarette or pencil, or some other commonly held and lightweight item. Set the point of that item along a ruler that perpendicular to the ground. The object will move up and down as the air pressure changes.
Plant scarlet pimpernel's in your garden or planter. Known as the shepherd's weather glass and the poor man's barometer, when the atmospheric pressure changes and a storm approaches, this flower closes it petals, and reopens them when the pressure normalizes.