Enquire within upon everything by Robert Kemp Philp

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.