Gary Beaudrie, age 13, of Louisville, Kentucky, for his question:

Which is the up and down of a river?

A river always flows downhill from its source. When fluid water is left to move freely it always flows down to seek its own level. From this we can assume that upstream is toward the source of a river and downstream is the opposite direction. The current flows from upstream and goes on its way downstream. Louisville stands by the magnificent Ohio, sweeping southwestward to empty its waters into the Mississippi. This direction is downstream. Upstream, against the current, takes you northeast to where the Allegheny and Monongahela rivers join to found the great Ohio near Pittsburgh.

It is not always easy to detect the gentle continental slopes that determine the course of our rivers. But as a rule, the direction of the flowing water points out the up and down of a stream. In deltas and wide river mouths, the changing tides do not

provide this information. But from there you usually know the general direction of the ocean    in which case, downstream is that a way. It is not hard to figure the up and down of a river    but Andy has never been about to tell which is up the street or down the street. He suspects that this depends on the personal opinion of who happens to be giving the directions.