“It’s a good deal better to be safe, than sorry, when you have girls under your care,” Dan Dalzell added.

The motor boat, a fast though a low-hulled craft, had been long out of sight up the river.  Presently there came a new turn to the wind.  Dan wet a forefinger and held it up to the breeze.

“I hope Foss has sense enough to run in somewhere and tie up until the coming squall blows over,” Dalzell remarked.

“Are we going to have a storm?” Belle asked quickly.

“Not rain, if that’s what you mean,” Darrin replied.  “But I believe the river is going to be pretty rough before long.”

Ere two minutes more had passed Dave suddenly rose and straightened himself.

“Look downstream, girls,” he cried.  “Do you see the big rollers coming?”

In truth the surface of the river was now beginning to behave in an unusual way.  Where, heretofore, the water had been choppy and whitecapped, the water now broke in longer, foam-crested waves.  Owing to the course of the wind the waves were rolling upstream.  Within five minutes from the time when Dave first called attention to the rougher water the waves had considerably increased in size.

“Oh, I’m glad I’m not out on the water,” shivered Laura.

“So am I,” Belle admitted candidly.

“Do you believe Tom Foss can bring his boat down against such waves!” Laura inquired.

“Oh, no doubt, he has had sense enough to run in somewhere and tie up,” predicted Midshipman Dan charitably.

“I hope so,” murmured Belle.  “But Tom is an awfully stubborn fellow.”

Toot! too-oo-oot! sounded a whistle up the river.

“By ginger, there comes Foss’s boat now!” muttered Dan, standing up and staring.  “Why doesn’t the idiot make land?”

“He’s got his craft away on the other side of the river, looking for quieter water,” muttered Dave uneasily.

“Well, isn’t that right?” asked Belle.

“Right, yes, unless he makes the mistake of trying to cross the stream,” nodded Darrin.  “Then he’ll run his craft into the trough of the sea, and—­”

“Well, what?” demanded Belle as Dave paused.

“Then, when he’s in the trough, a big wave may roll his small boat over,” Dan finished for his comrade.

“Do you really think there’s danger of that?” demanded Laura, looking anxious.

“I don’t know,” murmured Dave.  “But I wish I had some way of signaling Foss, some way so that he could understand the signals.”

“What good would it do?” demanded Midshipman Dalzell, grimly.  “Tom would only laugh and say it was more old maidishness on the part of Navy men.”

“There—­confound the idiot!” suddenly blazed Dave Darrin.  “He is crossing.  Look at that boat wallow in the trough.  Jupiter!  There she goes over—­nearly!”

All four young people on the float held their breath for an instant.  The motor launch, after almost having turned turtle, righted itself.