He had found the home of the aged inventor to be a fourth-floor back flat, being merely two dark rooms upon an alley. Here, with his wife, a pleasant-faced old lady, he lived and labored.
“You see,” he had said, as he uncovered the engine with the dramatic movement of one who unveils a great work of art, “this engine of mine is different from all other internal-combustion engines. It doesn’t burn gasoline; it burns dust.”
“Dust!” Johnny had exclaimed.
“Dust!” the old man had smiled. “Watch it!”
He touched a lever. There followed a succession of rapid and sharp explosions. These increased in number per second until they became a prolonged purr, as the one in the “mule” had done. The engine was now revolving at full speed.
“You see?” the old man had smiled. “She runs—on dust!”
“On dust,” Johnny had repeated in a daze.
The old man had touched the lever and the engine had stopped.
“You think it strange,” the old man had smiled, motioning Johnny to a chair and taking one himself; “but, after all, is it so strange? The first internal-combustion engine, we have it on good authority, did not burn gasoline but a composition of gun powder and other substances. The greatest grain elevator in the world was destroyed by a dust explosion. Billions of fine particles of carbon dust gathered in the air space above the wheat. A spark touched it off. A tremendous explosion followed. There is unlimited power there. Why not harness it?
“You are looking,” he pointed at the engine, “upon the motor power of the future. It ran, as you saw a moment ago, on coal dust, a very finely powdered coal dust. A little is let in at a time. A slight ash is formed. This drops out at the top of the cylinder, as you will see the engine runs inverted. It was burning coal dust, but any carbon dust will do. Wood ground fine, wheat dust, peat dust, any carbon dust will drive it. Think what that means to the world-traveler of the future! No more disgusting waiting for gasoline; no more weary miles on foot. You land in the heart of Africa, India, Siberia. You have with you a small grinder like a wheat mill. It is run by batteries. You are out of fuel. You merely grind up a dry tree-trunk, a sack of wheat or a few pounds of coal, and you are away again.”