Both the existence of Egypt itself, and its strange insulation in the midst of boundless tracts of dry and barren sand, depend upon certain remarkable results of the general laws of rain. What I mean is, that the water which is taken up by the atmosphere from the surface of the sea and of the land by evaporation, falls again, under certain circumstances, in showers of rain, the fre- quency and abundance of which vary very much in different portions of the earth. As a general principle, rains are much more frequent and abundant near the equator than in the temperate climes, and they grow less and less as we approach the poles. This might naturally have been expected; under the burning sun of the equator, the evaporation of water must necessarily go on with immensely greater rapidity than in the colder zones, and all the water which is taken up must, of course, again come down. It is not, however, wholly by the latitude of the region in which the evaporation takes place that the quantity of rain which falls from the atmosphere is determined.