“But your supply of petrol? Where have you sufficient space for a supply that will last any considerable length of time?” “All round us.” The professor swept their surroundings with his sharp eyes. No receptacle was visible. Two full-size doors and several small ones appeared in the partitions; but nothing suggested a receptacle for a large supply of fuel. Then quite suddenly it dawned upon him that there was a vast amount of space unaccounted for between the partitions, floor and ceiling, and the _Sphere’s_ outside shell. His respect for Robert’s claims was growing. So far, at least, the young inventor seemed quite confident. “What is this?” asked the professor, indicating what resembled the breech of a dreadnaught’s gun protruding from the floor. Electric wires, dials, and other curious devices were connected to it. “That’s the Norrensen Tube, so named by my father after its inventor, an old friend of his, now deceased. It is capable of terrible destruction. It will produce a bolt of lightning rivaling the elements, which will strike up to twelve miles away--and it can be aimed with startling accuracy. I remember seeing a giant oak blasted into pulp with it in a test across a valley four miles wide, when I was a boy.” “But, how is it that the world has never heard of this remarkable invention?” “Norrensen was an eccentric character whom the world had wronged grievously. He insisted on conducting the tests with greatest secrecy. Overtaken suddenly by a fatal illness, he exacted a promise from my father to retain the secret of this weapon till his death.” “What a terrible weapon that would make in the hands of a man bent on destruction!” mused the professor. The compartment they were in looked to be about twelve by twenty-five feet, and some ten feet in height. There were three round ports at either of its rounded ends; these, being located below the bulge of the _Sphere’s_ greatest girth, enabled one to obtain a good view downward as well as outward. The straight sidewalls and ceiling were windowless, but a vertical well extending from the floor, beside the controls, to the outer shell, with heavy, circular glass panes at either end, enabled the operator to see out directly below. The compartment was flooded with soft, mellow light from a dozen frosted incandescent lamps. “Deducting for this compartment, two small storerooms, the cupboards, and the water and oxygen tanks,” Robert was saying, “the net capacity of the petrol reservoirs is more than 40,000 gallons. That and the full storage power of the batteries is sufficient to operate the high-speed, but delicately balanced gyrostats, more than fifty days and nights continuously.” “You say that gravity is completely neutralized?” “Almost entirely so, even with all reservoirs filled to capacity. The stability of the gyrostatic device is so powerful that weight becomes a negligible factor. If you will follow me I can prove this to you.”