Egypt has always been considered as physically the most remarkable country on the globe. It is a long and narrow valley of verdure and fruitfulness, completely insulated from the rest of the habitable world. It is more completely insulated, in fact, than any literal island could be, inasmuch as deserts are more impassable than seas. The very existence of Egypt is a most extraordinary phenomenon. If we could but soar with the wings of an eagle into the air, and look down upon the scene, so as to observe the operation of that grand and yet simple process by which this long and wonderful valley, teeming so profusely with animal and vegetable life, has been formed, and is annually revivified and renewed, in the midst of surrounding wastes of silence, desolation, and death, we should gaze upon it with never-ceasing admiration and pleasure. We have not the wings of the eagle, but the generalizations of science furnish us with a sort of substitute for them. The long series of patient, careful, and sagacious observations, which have been continued now for two thousand years, bring us results, by means of which, through our powers of mental conception, we may take a comprehensive survey of the whole scene, analogous, in some respects, to that which direct and actual vision would afford us, if we could look down upon it from the eagle's point of view. It is, however, somewhat humiliating to our pride of intellect to reflect that long-continued philosophical investigations and learned scientific research are, in such a case as this, after all, in some sense, only a sort of substitute for wings. A human mind connected with a pair of eagle's wings would have solved the mystery of Egypt in a week; whereas science, philosophy, and research, confined to the surface of the ground, have been occupied for twenty centuries in accomplishing the undertaking. It is found at last that 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. 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 frequency and copiousness 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 temperate climes, and they grow less and less so as we approach the poles. This might naturally have been expected; for, 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.