"The water is very low this morning," said Forester, "and they have to proceed very carefully, or else they will get aground."
"What makes the water so low now?" asked Marco.
"There are two reasons," replied Forester. "It is late in the summer, and the streams and springs are all low; so that there is but little water to come down from the country above. Then, besides, the tide is low this morning in the sea, and that causes what water there is in the bed of the river to run off into the sea."
"Is not there any tide in the river?" asked Marco.
"No," said Forester, "I suppose there is not, strictly speaking. That is, the moon, which attracts the waters of the ocean, and makes them rise and fall in succession, produces no sensible effect upon the waters of a river. But then the rise and fall of the sea itself causes all rivers to rise and fall near their mouths, and as far up as the influence of the sea extends. You see, in fact, that it must be so."
"Not exactly," said Marco.
"Why, when the water in the sea," continued Forester, "at the mouth of the river is very low, the water in the river can flow off more readily, and this makes the water fall in the river itself. On the other hand, when the water in the sea is high, the water cannot run out from the river, and so it rises. Sometimes, in fact, the sea rises so much that the water from the sea flows up into the river, and makes it salt for a considerable distance from its mouth."
"I wonder whether the water is salt here," said Marco.
"I don't know," said Forester.
"If we had a pail with a long rope to it," said Marco, "we could let it down and get some, and try it."