By this time the boys were all lying prone around the big map, their feet radiating in every direction from it, like light-rays from a star. “See here,” said Ed; “here’s the Tennessee River. It’s a mere tributary of the Ohio, yet it is about two-thirds as long as the main river. Its head waters are in Virginia, North Carolina, and South Carolina. It starts out through Tennessee and tries, in a stupid sort of fashion, to find its way to the Gulf of Mexico through Alabama. But it gets discouraged by the mountains down there, turns back, throws a dash of water into the face of the state of Mississippi, returns to Tennessee and travels north clear across that state and Kentucky, and finally in despair gives up its effort to find the sea and turns the job over to the Ohio. Look at it on the map!” “And as if it thought the Tennessee had more than it could do to drain so great a region,” said Phil, studying the map, “the Cumberland also went into the business and after pretty nearly paralleling its sister river for a great many hundreds of miles, fell into the Ohio only a few miles above the mouth of the Tennessee. The two together are longer than the Ohio itself.” “Very decidedly,” said Ed. “And then there are all the other tributaries of the Ohio,--look at them on the map. Together they again exceed its total length.” The boys looked at the map and saw that it was so. Then Ed resumed:-- “But, after all, the Ohio and all its tributaries combined amount to a very small part of the great system. The lower Mississippi itself from Cairo to the mouth is almost exactly as long as the Ohio. Then there are the upper Mississippi,--stretching clear up into Minnesota,--the Illinois, the Wisconsin, etc., the Missouri and its vast tributaries flowing from the Rocky Mountains, the Arkansas, the Red River, the Ouachita, the White, the St. Francis, the Yazoo, the Tallahatchie, the Sunflower, the Yalobusha--and a score of others, to say nothing of the vast bayous that connect with the wonderful river down South. Here they all are on the map. Look!” The next fifteen minutes were given up to a study of the map, interested fingers tracing out the rivers, and a continual chatter contributing, after the manner of boys’ talk, to the general stock of information. Presently Irv Strong spoke. He had never before in his life been silent so long. “I remember, at this stage of the proceedings, the wise remark of our honored teacher, Mrs. Dupont, that ‘eyes are excellent to see with, but one interpretative brain means more than many additional pairs of eyes.’” “What’s all that got to do with it?” asked Constant. “She was talking about Darwin and Spencer when she said that. What’s either of them got to do with this river?”