We are all familiar with the so-called “sweating” of a glass or pitcher, or a metal pipe containing cold water; this is another phase of the dew, and may be observed in the daytime.
A cool night in spring or autumn, after a hot day, we usually receive a more copious fall of dew, which gradually increases as the night becomes cooler. Should clouds gather, the precipitation of the dew at once ceases. Wherever a bush or bit of vegetation overhangs a spot, it has a similar effect to that of a cloud, and the dew does not collect at all, or not as copiously, in that spot.
In the tropics, and in certain countries where there are no rain clouds; where they rarely have rain for many months at a time, the dewfall is so heavy that it quite supplies the lack of rainfall. If it were not for this providential visitation of the dew all vegetable life must certainly perish, scorched and withered by the torrid heat.
20. Like a piece of bleached coral. Hoar frost discovered under a building
21. Tabular hoar frost
22. Tree form tabular hoar frost: grew in zero weather
In the East, in the region of Palestine, the dew frequently is so heavy that it closely resembles rain. Upon the great burning deserts alone the dew never falls; for the moment the dew vapours or molecules encounter the scorching breath which arises from the face of these barren seas of sand, they evaporate and are redissolved, dissipated and consumed by the heat. So it will be seen that the fixed molecules which compose vegetation alone have the power to attract and arrest the water molecules of the air with which they come in contact, and thus form, in combination, the dew.