The Reason Why / A Careful Collection of Many Hundreds of Reasons for Things Which, Though Generally Believed, Are Imperfectly Understood

by Robert Kemp Philp

Fig. 20.—BAROMETER.

Fig. 21.—TUBE OF BAROMETER, WHEEL, AND PULLEY.

695. Why does the hand of the weather dial change its position when the column of mercury rises or falls?

Because a weight, which floats upon the open surface of the mercury, is attached to a string, having a nearly equal weight at the other extremity; the string is laid over a revolving pivot to which the hand is fixed, and the friction of the string turns the hand, as the mercury rises or falls.

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"Thou visitest the earth, and waterest it: thou greatly enrichest it with the river of God, which is full of water: thou preparest them corn, when thou hast so provided for it."—Psalm lxv.