Enquire within upon everything

Because the weight on the surface of the mercury frequently leans against the side of the tube, and does not move freely. And, also, the mercury clings to the sides of the tube by capillary attraction; therefore, tapping on the face of the barometer sets the weight free, and overcomes the attraction which impedes the rise or fall of the mercury. 978. Why does the Fall of the Barometer denote the Approach of Rain? Because it shows that as the air cannot support the full weight of the column of mercury, the atmosphere must be thin with watery vapours. 979. Why does the Rise of the Barometer denote the Approach of Fine Weather? Because the external air, becoming dense, and free from highly elastic vapours, presses with increased force upon the mercury upon which the weight floats; that weight, therefore, sinks in the short tube as the mercury rises in the long one, and in sinking, turns the hand to Change, Fair, &e. 980. When does the Barometer stand highest? When there is a duration of frost, or when north-easterly winds prevail. 981. Why does the Barometer stand highest at these Times? Because the atmosphere is exceedingly dry and dense, and fully balances the weight of the column of mercury. 982. When does the Barometer stand lowest? When a thaw follows a long frost, or when south-west winds prevail. 983. Why does the Barometer stand lowest at these Times? Because much moisture exists in the air, by which it is rendered less dense and heavy. [1]