Mr. Lochridge stooped down and took from a case, containing many more, a stick of dark-brown material about four feet long by one inch in diameter, and handed it to Cobb for his inspection, saying: "That is lipthalite. These rods are placed in those tubes, and, by proper mechanism, pushed through into the field of an arc light situated in the generator. Gas is evolved in great quantities, but the composition burns only while in the field of the arc. Little heat is developed. The gas is delivered to the cylinders in the same manner as was steam in your day." "What is the volume of gas as compared with the solid base? and is it cheaper and as efficient as vapor of water?" "I expected that question, Mr. Cobb," returned Mr. Lochridge, "and will explain it. One cubic foot of water, as you know, produces nearly 1,700 cubic feet of steam; one cubic inch of gunpowder makes about 1,500 cubic inches of carbonic acid and nitrogen gases; while one cubic inch of lipthalite will evolve 500 cubic feet of lipthalene, a combination of nitrogen, carbonic acid, and other gases. The ratio between water and lipthalite, evolved into gas, is as 1 to 500. In other words, to operate the engines of this vessel at a given speed for one hour, requires, of coal and water, one and thirty-one tons respectively; while of lipthalite, twenty-three pounds. Leaving out the question of water, of which there is a plentiful supply surrounding the vessel, the gain in a twenty-four hours' run for lipthalite over coal is as 1 is to 96; or one ton of lipthalite is used where ninety-six tons of coal would have been required." "It is a wonderful discovery!" exclaimed Cobb, and a far-away, dreamy expression came into his eyes. For an instant his mind went back to the days, long years ago, when he had spent hours in his laboratory, at the Presidio, searching for this very same agent--the storage of great power in small volume--and his partial success in the discovery of meteorite. Then his thoughts led him to the remembrance that his new explosive had been sent to Washington. What had become of it? Lost, lost, years ago! "Do you comprehend the advance in science that has been made in a hundred years?" and Rawolle broke his reverie by gently touching him on the arm. "Can I help it? Could anyone have dreamed of such a power as this?" Yes. He had dreamed of it; and many, many times. But too modest to venture the knowledge that his thoughts and work had been centered on such a grand invention, he turned to Mr. Lochridge, and abruptly asked: "Is lipthalite turned into gas by explosion?" "By no means," quickly returned that gentleman; "by inflammation, and inflammation alone, and not very fast, either. In our generators, here, it is at the rate of about two hundred and fifty feet of these sticks per hour." "Strange that I should have worked on this very principle!" he said, half aloud; then turning to Lieutenant Sibley, he exclaimed: "You spoke of water cylinders; where are they?"