Meantime the boat slowly drifted down the stream.  The water was here deep and comparatively still, and the boys amused themselves with looking over the sides into the depths of the water.  They glided noiselessly along over various objects,—­now a great flat rock, now a sunken tree, and now a bed of yellow sand.  Every now and then, Forester would order the oars out, and make the oarsmen give way for a few strokes, so as to give the boat what they called steerage way, that is, way through the water, so that holding the paddle in one position or the other would steer it.  In this way Forester guided the boat in the right direction, keeping it pretty near the middle of the stream.

This mill-stream, as has already been stated, emptied into the river, and the boat was now rapidly approaching the place of junction.  In a few minutes more the river came into view.  The boys could see it at some distance before them, running with great rapidity by a rocky point of land which formed one side of the mouth of the brook.

“Now, boys,” said Forester, “is it safe for us to go out into that current?”

“Yes,” said Marco, “by all means,—­let us go.”

“Perhaps we shall upset in the rips,” said some of the boys.

“No matter if we do,” said Marco; “it is not deep in the rips, and of course there is no danger.”

“That is in our favor certainly,” said Forester.  “Whenever the current sets strong, there it is sure to be shallow, so that if we upset we should not be drowned; and where it is deep, so as to make it dangerous for us to get in, it is always still, and thus there is no danger of upsetting.”

“What is the reason of that?” said one of the boys.

“The reason is given in this way,” said Forester, “in the college mathematics.  The velocity of a stream is inversely as the area of the section.”

The boys did not understand such mathematical phraseology as this, and so Forester clothed his explanation in different language.  He said that where the stream was shallow or narrow, the current must be more rapid, in order to get all the water through in so small a space, but where it is deep, it may move slowly.

Forester landed his crew upon the rocky point, where they had a very pleasant view up and down the river.  He proposed to them to have their luncheon there, and to this they agreed.  So they went back to the edge of the rocks, where there was a little grove of trees, and they sat down upon a log which had been worn smooth by the action of the water in floods, and bleached by the sun.

There were plenty of dry sticks and slabs lying about upon the shore, which Forester ordered the crew to collect in order to build a fire.  It was not cold, and they had no need of a fire for any purposes of cooking, but a fire would look cheerful and pleasant, and they accordingly made one.  Forester had some matches in his pocket.  Two of the crew brought the basket from the boat, and when they had opened it, they found an abundant store of provisions.  There was a dozen or more of round cakes, and a large apple-pie, which, as there were just eight of them, gave forty-five degrees to each one.  There was also a jug of milk, and a silver mug, which Forester’s mother had lent them for the excursion, to drink out of.