Do make a barometer with a wide-mouthed bottle, and a piece of toy balloon rubber. By fastening a piece of rubber over the mouth of a wide-mouthed bottle, you will trap the air of the moment inside, with that exact pressure of the day. Lowering outside pressure or rising outside pressure will then expand or depress the rubber cover. By gluing a “pointer” (a long light sliver of wood or straw) to one side of the rubber cover, the pointer will move up or down according to weather pressure changes. This gadget must be kept from direct sunlight or other heat which might cause the air inside to expand or contract from heat or cold. Even if not very accurate, this homemade machine explains the action and mechanics of the modern aneroid barometer.