in this shape. We remark how suitable and indispensable to the well-being of the creation it is, that the fluid should possess the property of assuming such a form under such circumstances.

The moisture which floats in the atmosphere is of most essential use to vegetable life.* The leaves of livi11g plants appear to act upon this vapour in its elastic form, and to absorb it. Some vegetables increase in weight from this cause when suspended in the atmosphere and uncon- nected with the soil, as the house-leek and the aloe. In very intense heats, and when the soil is dry, the life of plants seems to be preserved by the absorbent power of their leaves.” It follows from What has already been said, that, with an increasing heat of the atmosphere, an increasing quantity of vapour will rise into it, if supplied from any quarter. Hence it appears that aqueous vapour is most abundant in the atmosphere when it is most needed for the purposes of life; and that when other sources of moisture are cut ofl‘, this is most copious.

4. Clouds are produced by aqueous vapour when it returns to the state of water. This process is condensation, the reverse of evaporation. \Vhen vapour exists in the atmosphere, if in any manner the temperature becomes lower than the con- stituerzt tenzperatzzre, requisite for the maintei

* .011don. P219.