VII. THE WONDERFUL EYE OF THE SUBMARINE 129

VII. THE WONDERFUL EYE OF THE SUBMARINE 129

How the Eye of the Submarine Got Its Name.—The First Submarine Eye, or Periscope.—How to Make a Simple Periscope.—The Modern Lenticular Periscope.—How the Telescope Is Made.—The Latest Type of Periscope.—The Limited Use of the Periscope.—The New Enemy of the Submarine.

VIII. THE MARVELOUS TONGUE AND EARS OF THE SUBMARINE 143

The Tongue and Ears of a Submarine.—Kinds of Signaling Systems.—The Wigwag Way of Signaling.—The Flashlight System.—The Wireless Telegraph System.—Underwater Signaling Systems.—The Electric Current, or Conductivity System.

IX. THE CREW OF THE SUBMARINE 159

Conditions on Early Submarine Craft.—When Crews Were Hard to Sign.—What the Base-Ship Is For.—How Men Are Trained for Submarine Duty.—The Complement of a Submarine.—Breaking in Raw Recruits.—The Conditions in War Time.