"W HAT is needed to make the half-condensed vapor of clouds finish condensing and turn to water, falling in drops of rain? Very little: a slight cooling, a breath of cold air from some less heated region.
"As soon as it is cooled the fine aqueous dust of the clouds, similar to what we see rolling up in the form of fog, collects in very small drops which fall of their own weight.
"In passing through the dense mist below them these droplets condense on their surface a little of the vapor they meet with, so that they increase in size and become drops capable of growing still larger, until the very moment of their leaving the clouds. Finally they fall to the ground after attaining a size proportioned to the thickness of the cloud-layer through which they have passed.
"That is rain—one day a fine shower which hardly bends the blades of grass, another day a heavy downpour in big drops that patter on the foliage and the tiled roofs. That, I say, is rain which we all so eagerly desire when the country is suffering from drought.
"It rains beneath the clouds that are converted into water by being chilled; but elsewhere it does not rain, the sky is blue, and the sun shines. One can often see this uneven distribution of a rainfall. Has it not happened to you that, with the sky all blue overhead, you have seen in the distance something like a vast grayish curtain, vertically striped and reaching from the sky to the earth? That is a cloud turning into rain and pouring out its contents wherever it passes. It may even have reached you, driven in your direction by the wind. Then the blue sky has suddenly become somber, and you are caught in a shower.
"Clouds may be likened to immense celestial watering-pots that travel almost everywhere at the caprice of the winds that drive them. Every region they visit receives a shower; but any other, however near it may be, receives nothing so long as it does not lie under them. A rainfall may be local in extent and its limits so sharply defined that a few steps in one direction will expose you to a shower and a few steps in the other place you where not a drop falls. But local rains are not the only ones. There are some—and they often occur—that embrace enormous regions, several provinces at a time.
"While the rain is falling, as we may imagine it to fall, let us consider for a moment the marvelous journey accomplished by a single raindrop. Whence does it come? From the clouds floating there above our heads, perhaps one or two thousand meters high. It was up there when the thunder burst; it was present at the blinding flash of the lightning. But no sooner was it formed than, by the force of its own weight, it fell with dizzy speed from its lofty position. Behold it rebounding from a leaf and falling to the ground, where it soaks into the soil and adds to the moisture essential to the life of every plant. A head of lettuce, perhaps, in drinking it, will gain renewed vigor.
"It came from the clouds, and clouds are made of vapor held in the atmosphere. This in turn results from the evaporation of water, chiefly the water of the sea, by the heat of the sun. But of what sea? Who can say? Who could indicate precisely from what point of the broad ocean's surface the sun drew the vapor that was one day to form that drop? Was it from the blue waves of the Mediterranean, the smiling sea to the south of France? It is possible, if the cloud from which it fell was driven so far by the south wind. Or was it from the greenish waves of the ocean whose billows dash furiously against the cliffs of Normandy and the reefs of Brittany? Possibly, if the west wind drove hither the cloud that was to let it fall.
"It is possible, again, that the raindrop came from a far greater distance, perhaps from some gulf fringed with cocoanut-trees whereon perch green parrots with red tails; perhaps from some arm of the sea where the whale suckles its young; perhaps from the other end of the world. Yes, there are all these possibilities; and then what a journey to come to us and water a head of lettuce!
"This prodigious journey ended, is our drop of rain at last to find rest in the plant it has watered? By no means. Nothing remains at rest in this world, not even a drop of water. Everything is in motion, everything is busy, everything is forever beginning again the task already accomplished.
"The drop of water rises with the sap from the roots of the plant, ascends through the stalk, and reaches the leaves, where it evaporates. The heat of the sun reduces to vapor what it had for a moment relinquished to the earth as water. And so we have again the drop of water high in the heavens and transformed to an invisible state—once more given over to the caprices of wind and storm, which will carry it no one knows whither. One day or another it will become rain again, and there is no reason why it should not, sooner or later, water the cocoanut-tree from the neighborhood of which we supposed it to start.
"These journeys being repeated unceasingly, sometimes in one direction, sometimes in another, the raindrop cannot fail some day to rejoin the sea whence it originally came. All rain comes ultimately from the sea, and to the sea all rain finally returns."