The Story Book of Science  by Jean Henri Fabre


"T HE explanations of this morning account for the formation of clouds. A continual evaporation takes place on the surface of the damp earth as well as on the surface of the different sheets of water, lakes, ponds, marshes, streams, and above all the sea. The vapors formed rise into the air and remain invisible as long as the heat is sufficient. But since heat diminishes as the height increases, there comes a time when the vapors can no longer be kept in complete solution, and they condense into a mass of visible vapor, into a fog or cloud.

"When, after a chill encountered in the upper strata of the atmosphere, the cloud-mist reaches a certain degree of condensation, little drops of water form and fall in rain. At first very small, they increase in volume on the way by the union of other similar little drops. Their size on reaching us is proportioned to the height from which they fell, but never exceeds the limits suitable to the part rain is intended to play. If too large, the rain-drops would fall heavily on the plants they are to water, and would lay them flat on the ground, dead. And what would happen if the condensation of vapor, instead of taking place gradually, should be sudden? There would no longer descend from heaven rain-drops, but heavy columns of water, which, in their fall, would strip the trees of their branches, crush the harvests, and make the roofs of our houses fall in. But, far from taking this devastating form, rain falls in drops as if passed through a sieve placed by design in its passage to divide it and weaken the shock. On rare occasions, it is true, rain does reach us under so strange a disguise as to strike the ignorant with terror. Who would not be frightened when it rains blood or sulphur?"

"What do you say, Uncle?" interrupted Emile; "rains blood or sulphur? For my part, I should be dreadfully afraid."

"I too," said Claire.

"Is that true?" Jules asked, in his turn.

"True. You know well I only tell you true stories. There are rains of blood and sulphur, at least in appearance. It is proved that showers have been seen of which the drops left on the walls, roads, leaves of the trees, and clothes of passers-by, are red spots like blood. At other times, with the rain, there has fallen from the sky a fine dust, of a beautiful yellow, resembling sulphur. Did it really rain blood, sulphur? No. This so-called rain of blood or sulphur, causing foolish alarms, is ordinary rain stained with various sorts of dust raised from the ground by the wind. In the spring when, in mountainous countries, immense forests of fir-trees are in blossom, every breath of wind carries clouds of a fine yellow dust contained in the little flowers of the fir-tree. You can see a similar dust in all flowers, especially the lily."

"It is that dust that daubs your nose yellow when you smell a lily too close," declared Jules.

"Exactly. It is called pollen. Well, in falling at a distance, sometimes alone, sometimes accompanied by rain, the pollen gathered up from the forests by a breath of wind causes the so-called sulphur-rain."

"Your rain of blood or sulphur isn't at all terrifying," Claire remarked.

"Of course not; and yet whole populations have their hearts frozen with fear at the inoffensive fall of a whirlwind of pollen or red dust. They believe themselves visited with plagues, precursors of the end of the world. Ignorance is a pitiful thing, my dear children, and knowledge is a fine thing, even if it only served to deliver us from stupid terrors."

"In future," said Jules, stoutly, "it can rain sulphur or blood; if any one is afraid, it will not be I."

"There can also fall from the sky, with or without rain, various mineral substances, such as sand, for example, or powdered chalk, or dust from the roads. There is even mention of showers of small animals, caterpillars, insects, and very young toads. The marvelous feature of these rains disappears if one considers that a violent blast of wind can carry with it all light substances encountered in its course, and can transport them long distances before letting them fall again.

"At other times a rain of insects is due to something else besides transportation by the wind. Some kinds of grasshoppers, for example, gather together in immense swarms to go to another district when nutriment fails them. The emigrating band flies, as at a given signal, and passes through the air in the form of a great cloud that intercepts the daylight. The migration continues for days at a time, so numerous is the host. Then the voracious swarm alights, like a living storm, on the vegetation of some distant province. In a few hours grass, leaves of trees, grain, prairies—everything is browsed. The soil, as if ravaged by fire, hasn't a blade of grass left. Sometimes the people of Algeria die of hunger. The grasshopper has devoured their harvests.

"Volcanoes cause cinder-showers. Volcanic ashes is the name given to the calcined dust thrown up to a great height by volcanoes at the moment of their eruption. These powdered substances form enormous clouds, which produce in the daytime a darkness like that of the darkest nights, and which, falling to earth at a greater or less distance, stifle animals and plants under their showers of dust."