“It won’t take us long to sound the deep spots in this little harbor,” said the young skipper, as he dropped down once more into the bow of the shore boat.  “Row about, Hal, over the places where the submarine could go below out of sight.”

As Hal rowed, Skipper Jack industriously used the sounding-lead.

For twenty minutes nothing resulted from this exploration.  Then, all of a sudden, Benson shouted: 

“Back water, Hal!  Easy; rest on your oars.  Steady!”

Jack Benson raised the lead two or three feet, then let it down again, playing it up and down very much as a cod fisherman uses his line and hook.

“I’m hitting something, and it is hardly a rock, either,” declared young Benson.  “Pull around about three points to starboard, Hal, then steal barely forward.”

Again Benson played see-saw with his sounding-line over the boat’s gunwale.

“If my lead isn’t hitting the ‘Farnum,’” declared the young skipper, positively, “then it’s the ‘Farnum’s’ ghost.  Hold steady, now, Hal.”

Immediately afterward, Benson caused the lead fairly to dance a jig on whatever it touched at bottom.

“What’s the good of that, anyway?” demanded Jacob Farnum.

“You don’t think I’m doing this just for fun, do you, sir?” asked Captain Jack, with a smile.

“No; I know you generally have an object when you do anything unusual,” responded the shipbuilder, good-humoredly.

“You know, of course, sir, that noises sound with a good deal of exaggeration when you hear them under water?”

“Yes; of course.”

“You also know that all three of us have been practicing at telegraphy a good deal during the past few weeks, because every man who follows the sea ought to know how to send and receive wireless messages at need.”

“Yes; I know that, Benson.”

“Well, sir, I guess that the lead has been hitting the top of the ‘Farnum’s’ hull, and I’ve been tapping out the signal—­”

“The signal, ‘Come up—­rush!’” broke in Hal, with an odd smile.

“Right-o,” nodded Jack Benson.

“How on earth did you know what the signal was, Hastings?” demanded Mr. Farnum.

“Why, sir, I’ve been sitting so that I could see Jack’s arm.  I’ve been reading, from the motions of his right arm, the dots and dashes of the Morse telegraph alphabet.”

“You youngsters certainly get me, for the things you think of,” laughed the shipyard’s owner.

“And the ‘Farnum,’ or whatever it is, is coming up,” called Captain Jack, suddenly.  “I just felt my lead slide down over the top of her hull.  Hard-a-starboard, Hal, and row hard,” shouted young Benson, breathlessly.

Though Hastings obeyed immediately he was barely an instant too soon.  To his dismay, Mr. Farnum saw something dark, unwieldy, rising through the water.  It appeared to be coming up fairly under the stern of the shore boat, threatening to overturn the little craft and plunge them all into the icy water.