tarding effect of the current longer than she has the benefit of its
cooperation.

"For example," continued Mr. George, "suppose the distance from one
place to another, on a river flowing two miles an hour, is such that it
takes a steamer three hours to go down and four hours to come up. In
going down she would be aided how much?"

"Two miles an hour," said Rollo.

"And that makes how much for the whole time going down?" asked Mr.
George.

"Six miles," said Rollo.

"Now, it takes her _four_ hours to go up," said Mr. George. "How much
would she be kept back then by the current?"

"Why, two miles an hour for _four_ hours," said Rollo, "which would make
eight miles."

"Thus in the double voyage," said Mr. George, "the boat would be helped
_six_ miles and hindered _eight_, so that the current would on the whole
be a serious disadvantage. For a steamer, therefore, which is to be
navigated equally both ways, the current is an evil.

"But for that sort of navigation which goes only one way, it is a great
advantage. For instance, the rafts have to come down, but they never
have to go back again; and so they have the whole advantage of the
current in bringing them down, without any disadvantage to balance it.

"On the whole," said Mr. George, "I do not see but that the currents of
great rivers are an advantage, for there is always a much greater
quantity to come down than to go up. The heavy products that grow on the
borders of the rivers are to come down, while comparatively little in
quantity goes up. So the benefit, on the whole, which is produced by the
flow of the water, may be greater than the injury."

"What do they do with the rafts," said Rollo, "when they get them down
the river?"

"They break them up," said Mr. George, "and sell the timber in the
countries near the mouth of the river, where but little timber grows."

By this time, Mr. George and Rollo had finished eating the meats which
they had ordered for their dinner, and so the waiter came and took away
the plates, and brought the omelet and the coffee. With the coffee the
waiter brought two small plates and knives, and some very nice rolls and
butter. He also brought a plate containing several slices of a kind of
cake, _toasted_. This cake was very nice.

While Rollo was eating it he asked his uncle George whether, in case he
had gone down the river to Boppard, and had not got back until dark, he
should not have been anxious about him.

"No," sa