Enquire within upon everything

[NOR BREAK THE TIES OF FRIENDSHIP NEEDLESSLY.] 973. Hints on the Barometer. 974. Why does a Barometer indicate the Pressure of the Atmosphere? Because it consists of a tube containing quicksilver, closed at one end and open at the other, so that the pressure of air upon the open end balances the weight of the column of mercury (quicksilver); and when the pressure of the air upon the open surface of the mercury increases or decreases, the mercury rises or falls in response thereto. 975. Why is a Barometer called also a "Weather Glass"? Because changes in the weather are generally preceded by alterations in the atmospheric pressure. But we cannot perceive those changes as they gradually occur; the alteration in the height of the column of mercury, therefore, enables us to know that atmospheric changes are taking place, and by observation we are enabled to determine certain rules by which the state of the weather may be foretold with considerable probability. 976. Why docs 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. 977. Why does Tapping the Face of the Barometer sometimes cause the Hand to Move?