touched on bottom.

While this was going on, the long-legged stranger, wholly absorbed in
his own work, made some observations and some hurried calculations.
Then he pulled the drawing-board toward him, jotting down a point.

Jack Benson, standing stealthily, got a good look, for the first time,
at the top of that drawing board.

"A chart of the bay, of course," muttered Benson, savagely, between his
teeth. "The fellow is marking down the exact position of that mine!"

Still, the submarine boy did nothing to betray his own presence. He
watched and wondered. The thought struck him that this long-legged
one might be an officer of the Army, on observation duty like the
submarine boy himself.

"But that isn't right; I'm sure it isn't," decided young Benson, quickly.
"If they fellow were here on honest business, he wouldn't have sneaked
out here to get in position. Besides, I have a vague remembrance of
this fellow, and I don't connect him with anything honest!"

The Army tug, out on the bay, was now engaged in planting a second mine.
Again the slim stranger was all attention. When the crane began to
lower the mine, a second mark was made on the chart on the drawing
board.

Now, once more, the fellow lay at full length, watching intently off
over the bay. At his right hand lay drawing-board, the book and the
field-glasses.