In effect, the periscope is a device which in the main is like a pipe; it can be pushed up through the top of the conning tower, through a special, water-proof cylinder, until the top of the periscope is a foot, or less, above the surface of the water.
The top of this instrument is fitted with lenses and mirrors. Down through the shaft of the periscope are other mirrors, which pass along any image reflected on the uppermost mirror of all. At the bottom of the periscope is the last mirror of the series, and, opening in upon this, there is an eyepiece fitted with a lens.
As Captain Jack Benson applied his right eye to the eyepiece he was able to see anything above the surface of the water that lay in any direction that the periscope was pointing.
"Right opposite Spruce Beach, as the chart showed!" chuckled the young commander. Under the magnifying effect of the eyepiece lens Benson could see the beach, the flag-bedecked hotels, and the moving masses of people on the shore. Yet, all this time, he was out at sea, more than a mile from the beach. The periscope itself, if seen from a boat an eighth of a mile away, would undoubtedly have been taken for a floating bottle.
"Let me have a peep," demanded Somers.
Eph looked briefly, then chuckled:
"Must be thousands of people over yonder, wondering what on earth has happened to us!"
"Do you make out the gunboat, at anchor to the north of the hotel section?" inquired Captain Jack.
"Oh, yes. Say, they'll have an awakening on that gray craft, won't they?"
"If we don't make any slip in our calculations," answered Benson, gravely.