Oilers holding oil cans and waste clambered in and out of the rotating masses of iron with astounding sureness and boldness. To graze one of the fly-wheels, or to step one inch within the unguarded circle of their revolution, was to receive a deadly blow. Here was the heart and soul of the vessel, the real modern miracle of strength, the like of which no age in the past has been able to produce. An iron soul, a steely heart. It was as if one were descending below earth into the glowing workshop of Vulcan of old, the lame god, who did not demonstrate the full skill of his divinity until our times. Still deeper down went the descent, to where, from numerous shovels handled by almost naked helots, coal was flying into the white heat under the boilers, into a row of gaping jaws of fire. Frederick felt as if he had reached the heart of a crater. It was a black shaft smelling of coal, slag, and burning things. Apparently it was lighted only by the constant opening of the furnace doors, spitting white heat. How was it possible for such a conflagration to be contained in the _Roland's_ interior without reducing the whole to ashes? What a conquest to fight such a sea of fire, to keep it in check, and carry it through sea and storm; to manage that it should carry itself three or six thousand miles in the ocean in fair weather or foul, hidden away and absolutely innocuous. Frederick panted for breath. The glowing heat of the abyss instantly brought the perspiration pouring out on his face and neck. He was so absorbed in the novelty of the impressions that he completely forgot he was surrounded by water about twenty feet under the surface of the sea. Suddenly, he became aware of Doctor Wilhelm's presence, and in the same instant saw a man entirely naked stretched out like a corpse, a white body on the black coal dust. The man had ceased to breathe. In a second Frederick, now wholly the physician, had Doctor Wilhelm's stethoscope in his hand and was listening to the man's heart. His mates, blackened with coal from head to foot, were ceaselessly at work in the engine's unremitting service, shovelling coal, opening the furnace doors, and slamming them shut. They scarcely cast a glance at their fallen comrade, and that only when they stopped to gulp a glass of beer or water. "It was hardly three minutes ago," said Doctor Wilhelm, "that he broke down. That man over there, the one who has just washed himself, is his successor."