Stewart, Balfour, 1828-1887 · Toronto : James Campbell · leaf 52
l in telling us whenbad weather is at hand. When the barometer falls,that is to say, when the top of the column of mercurygets lower in the tube and especially when it fallsquickly, we may expect bad weather. On the otherhand, if the mercury remains steady and high we mayexpect a continuance of… … Fig. 17, you what is meant by a valve. A valve is just atightly fitting trap-door that closes a hole, and that canonly open in one way—upwards, for instance. Youhave, most of you, seen trap-doors in floors that openupwards, Now in the figure you see to the left a bell-jar full of air, which fits…
Physics
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