THERE were two branches of the Hydraulic: one followed the course of the Miami, from some unknown point to the northward, on the level of its high bank, and joined the other where it emptied into the river just above the bridge. This last came down what had been a street, and it must have been very pretty to have these two swift streams of clear water rushing through the little town, under the culverts, and between the stone walls of its banks. But what a boy mainly cares for in a thing is _use_, and the boys tried to make some use of the Hydraulic, since it was there to find what they could do with it. Of course they were aware of the mills dotted along its course, and they knew that it ran them; but I do not believe any of them thought that it was built merely to run flour-mills and saw-mills and cotton-mills. They did what they could to find out its real use, but they could make very little of it. The current was so rapid that it would not freeze in winter, and in summer they could not go in swimming in it by day, because it was so public, and at night the Basin had more attractions. There was danger of cutting your feet on the broken glass and crockery which people threw into the Hydraulic, and though the edges of the culverts were good for jumping off of, the boys did not find them of much practical value. Sometimes you could catch sunfish in the Hydraulic, but it was generally too swift, and the only thing you could depend upon was catching crawfish. These abounded so that if you dropped a string with a bit of meat on it into the water anywhere, you could pull it up again with two or three crawfish hanging to it. The boys could not begin to use them all for bait, which was the only use their Creator seemed to have designed them for; but they had vaguely understood that people somewhere ate them, or something like them, though they had never known even the name of lobsters; and they always intended to get their mothers to have them cooked for them. None of them ever did.