“I HAVE been told,” said Emile, “that the Rhone empties its waters into the sea.”

“The Rhone does run into the sea,” returned his uncle. “It pours into it every second five million liters of water.”

“Receiving so much water continually, does not the sea end by overflowing, like a basin, when it is too full?”

“You are out in your reckoning, my dear child. The Rhone is not the only river that goes to the sea. In France alone there are the Garonne, Loire, Seine, and many less important ones. And that is only a very small part of the streams that flow into the sea. All the rivers in the world join it, absolutely all. The Amazon, in South America, is 1400 leagues long, and ten leagues wide at its mouth. What an immense quantity of water it must furnish!

“Imagine that all the streams in the world, small as well as large, the tiniest brooks no less than the enormous rivers, flow unceasingly into the sea. You know the little brook with the crabs. In certain places Emile can jump across it; scarcely anywhere is the water over his knees. Well, the brook goes to the sea exactly as the Amazon does; every second it casts its few liters of water into it; that is all it can do. But it does not dare, tiny little stream, to make the voyage alone and go and find the sea, the immense sea, all by itself. It meets company on the way, joins its thread of clear water to stronger streams which become rivers by joining their forces; the sea-going-river receives tributary streams, and the sea, in receiving the river, drinks the tiny brook.”

“All running waters,” said Jules, “brooks, torrents, streams, rivers, run into the sea without a break, and that takes place all over the world, so that every second the sea receives incalculable volumes of water. So I come back to Emile’s question: How is it that, continually receiving so much water, the sea does not overflow?”

“If, when full, a reservoir receives from a spring just as much as it lets out through some opening, can this reservoir overflow, even when water is always coming in?”

“Certainly not: losing as much as it receives, it must always keep the same level.”

“It is the same with the sea. It loses just as much as it gains, and therefore its level always remains the same. Brooks, torrents, streams, rivers, all run into the sea; but brooks, torrents, streams, and rivers also come from the sea. They carry back to the immense reservoir what they took from it, and not a drop more.”

“If the crab brook comes from the sea,” interposed Emile, “as you say, its water ought to be salt; but I know very well it is not, in the least.”

“Certainly it is not salt; but the brook does not come out of the sea as the water of a ditch comes from a reservoir. In coming from the sea, before becoming what it is, the brook has............