Health on the island. Illness of Harry. Fever. Determining temperature. Making a thermometer. Substitutes for glass and mercury. How Fahrenheit scale is determined. Centigrade scale. Testing the thermometer. Determining fever. Danger point. Why a coiled pipe tries to straighten out under pressure. Medicine for fever. Rains and rising Cataract River. Decision to explore sea coast to the east. Yoking up the yaks. Gathering samples of plants and flowers. The beach. Following the shore line. Discovering the boat which had disappeared from the Falls in South River. Surprising find of strange oars and unfamiliar rope in the boat. Harry and George decide to sail the boat around the cliff point to the Cataract River. The Professor takes the team home. Sighting an object on the cliffs. Going ashore at the foot of the cliffs for an examination. Ascending the cliffs. Discovering the wrecked remains of their life-boat. Consternation when their boat is washed away from the shore. Getting the wreck of the life-boat down to the water. The watching and waiting Professor. The boys launch the life-boat and float to the mainland. Meeting the Professor. Explanations.

Theory that their island is near some other inhabited island. The mysterious occurrences of the fire in the forest; the lights across the river. The disappearance of their boat. The removal of the flagpole and flag; the arrows; the hole in the hillside; the finding of the boat with unfamiliar oars and rope on it. Conclude to make another boat. Unsanitary arrangement of their kitchen. Purifying means employed. Different purifying agents. Primary electric battery. The cell; how made. The electrodes. Clay. The positive and the negative elements. How connected up. The battery. Making wire. How electricity flows. Rate of flow. Volts and amperes. Pressure and quantity. Drawing out the wire. Tools for drawing the wire. Friction. Molecules and atoms. Accomplishments of "Baby." Climbing trees and finding nuts. George as cook. Making puddings. "Baby's" aid. Finding eggs of prairie chicken. Planning a surprise for the Professor. The birthday party. George's cakes to celebrate the event. Harry's gong. The missing cakes. "Baby" the thief. The feast. Why laughter is infectious. Odors. Beautiful perfumes wafted to long distances. Bad odors destroyed. Why. Oxygen as a purifying agent.

The Cataract water. Common oak chips as purifiers. Tannic acid. Bitter almonds. Universal purification of water. The Bible method. Albumen impurities in water. Electric battery. The electrode. How the cells were made. Object of plurality of cells. Volts, amperes and watts, and their definitions. A new boat determined on. Determining size of the boat. Recovering their life-boat. Visit to Observation Hill. Hunting for the lost flagpole and flag. Wreckage of a ship's boat discovered. The Professor sent for. Ascertain it is not part of their wrecked boat. Gathering up portions of the boat. Amazing discovery of skull and skeleton. Methods of determining age. Condition of the skull and teeth. Carrying the remains to the Cataract. The funeral. The seven ages in the growth of man. Sadness. The skeleton at the feast. Why is death necessary. One of the many reasons.

The endive. Chicory. The principle in the plant. The root. Curious manner of preparing it. A surprise for Harry. Making clay crocks. How to glaze or vitrify them. The use of salt in the process. A potter's wheel. Uses of the wheel. Its antiquity. Inspecting the electric battery. How it is connected up. Peculiarities in designating parts of the battery. Making the first spark. Necessary requirements for making a lighting plant. The arc light. What arc is and means. The incandescent light. Why the filament in bulb does not readily burn out. Oxygen as a supporter of combustion. Carbon, how made. Essential of the invention of the arc light. Determine again to explore cave. The lamps, spears and other equipment. Exciting discovery of a sail. Signaling the ship. The ship disappears. Discouragement. Determine to make a large flag and erect a new flagpole. Visiting the cave. Exploring it. Mounting one of the lamps on ledge for safety. Water not found where it was on previous visit. Discovery of a large domed chamber. Bringing forward the light on the ledge. Entering the chamber. Disappearance of the light from the ledge. The outlet of the chamber. Searching for the lost light. Determine to chart the cave. Steps taken. Surveying methods. Substitutes for paper and pencil. Soot. The base, the angle, and the projecting lines. How the side walls were charted.

An eventful day. Accounting for the disappearance of the water in the cave. The animal in the cave. Subterranean connection with the sea. Starting to make the large flag. Regulation flag determined on. The stripes and their colors, and how arranged. Their significance. The blue field and how studded. Its proportional size. How the yellow ramie cloth was made white. The bleaching process. Chloride of lime. The red color. The madder plant. Its powerful dyeing qualities. Coffee. The surprise party for Harry. Chicory leaves as a salad. Exhilarative substances and beverages. The cocoa leaf. Betel-nut. Pepper plants. Thorn apples. The ledum and hop. Narcotic fungus. "Baby's" experiment with the red dye test sample. Test samples in dyeing. Color-metric tests in analyzing chemicals. Reagents. The meaning and their use. Bitter-sweet. Blue dye. Copper and lime as coloring substance. The completed flag. A hunting trip for the pole. Making a trailer. A pole fifty feet long determined on. Tethering the yaks at the river. Searching for pole. The shell-bark hickory. The giant ant-killer. His peculiarities. Weight of hickory. Weight of the pole. Problem to convey it to the river. Determine to get the yaks. Swimming them across the river. The Professor absent on their return. Searching for the Professor. A shot heard. Going in the direction of the shot. Another shot from vicinity of the team. Returning in the direction of last shot. Find the Professor with team on way to river. How they made a circle without knowing it. A lesson in judgment.