. Captain Jack
Benson unlocking the door to the conning tower, was himself the first to
disappear down below. When he came back he carried a line to which was
attached a heavy sounding-lead.

"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, fo