constantly accumulating through evaporation from seas and oceans and from the earth's surface, would have to find some other means of returning to its source. One of these modes would be the deposition of dew, which is itself an illustration of the principle that vapour requires solid or liquid surfaces to condense upon; dew forms most readily and abundantly on grass, on account of the numerous centres of condensation this affords. Dew, however, is now formed only on clear cold nights after warm or moist days. The air near the surface is warm and contains much vapour, though below the point of saturation. But the innumerable points and extensive surfaces of grass radiate heat quickly, and becoming cool, lower the temperature of the adjacent air, which then reaches saturation point and condenses the contained atmosphere on the grass. Hence, if the atmosphere at the earth's surface became super-saturated with aqueous vapour, dew would be continuously deposited, especially on every form of vegetation, the result being that everything, including our clothing, would be constantly dripping wet. If there were absolutely no particles of solid matter in the upper atmosphere, all the moisture would be returned to the earth in the form of dense mists, and frequent and copious dews, which in forests would form torrents of rain by the rapid condensation on the leaves. But if we suppose that solid particles were occasionally carried higher up through violent winds or tornadoes, then on those occasions the super-saturated atmosphere would condense rapidly upon them, and while falling would gather almost all the moisture in the atmosphere in that locality, resulting in masses or sheets of water, which would be so ruinously destructive by the mere weight and impetus of their fall that it is doubtful whether they would not render the earth almost wholly uninhabitable.