in the opposite direction; and prevents 0r much retards that continual flow of hot vapour into colder regions, by which a constant precipitation would take place in the latter situations.

If, in this state of things, the flow of the current of air, which blows from any colder place into a warmer region, be retarded or stopped, the aqueous vapours will now be able to make their way to the colder point, where they will be precipitated in clouds or showers.

Thus, in the lower part of the atmosphere, there are tendencies to a current of air in one direction, and a current of vapour in the opposite; and these tendencies exist in the average weather of places situated at a moderate distance from the equator. The air tends from the colder to the warmer parts, the vapour from the warmer to the colder.

The various distribution of land and sea, and many other causes, make these currents far from simple. But in general the air current pre- dominates, and keeps the skies clear and the moisture dissolved. Qccasional and irregular occurrences disturb this predomiiraiice; the mois- ture is then precipitated, the skies are clouded, and the clouds may descend in copious rains.

These alternations of fair weather a11d showers appear to be much more favourable to vegetable and animal life than any uniform course of weather could have been. To produce this