Page:Weather Facts and Predictions.djvu/13

 before the conclusion of a gale, sometimes even at its commencement, as the equilibrium begins to be restored.

Though the barometer falls lowest previous to high winds, yet heavy rains often cause a great depression.

Thunder and lightning are frequently preceded by a fall in the barometer, but an exception presents itself when the thunder-clouds come from the N.E.

Instances of fine weather, notwithstanding the barometer is low, occur from time to time, but they are always preludes to a duration of wind or rain, or both.

After any warm and calm weather a squall or storm with rain may follow; likewise at any time when the atmosphere is heated much above the usual temperature of the season, and when there is, or recently has been, much electric (or magnetic) disturbance in the atmosphere.

In examining the barometer for the purpose of forecasting the weather, the position of the mercury during previous days or hours should not be neglected, for an indication at any particular moment may be affected by causes operating at a distance and not visible to the observer whose barometer feels their effect. Or, as Admiral Fitzroy put it, "There may be heavy rain or violent winds beyond the horizon and the view of an observer, by which his instruments may be affected considerably, though no particular change of weather occurs in his immediate locality."

The longer a change of wind or weather is foretold before it occurs, the longer the