A BOY’S BAROMETER.
Take a common vial, or small bottle, cut off the rim by using the hot poker as directed above. Let the vial now be nearly filled with common rain water, and applying the finger to its mouth, turn it quickly upside down: on removing the finger it will be found that only a few drops will escape. Without a cork or stopper of any kind, the water will be retained within the bottle by the pressure of the external air, the weight of the air without the vial being so much greater than the small quantity within it. Now let a bit of tape be tied round the middle of the bottle, to which the two ends of a string may be attached, so as to form a loop to hang on a nail; let it be thus suspended in a perpendicular manner, with the mouth downward: and this is the barometer.
When the weather is fair, or inclined to be so, the water will be level at its lower surface, or perhaps concave, like an individual butter plate turned upside down; but when disposed to be stormy, a drop will appear at the mouth, which will enlarge till it falls, and then another drop, so long as the humidity of the atmosphere continues.
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