"Okay, okay," Richards said. "We determined the mass of the fuel tank, and therefore of the fuel in it. The tank contains a degenerate gas...." "What?" "A degenerate gas," Richards repeated. "The stuff must weigh several tons per spoonful." Dr. Petchkovich, the astronomer, frowned puzzledly. "Wait a minute. Degenerate gases are found only in the cores of certain types of stars ... are you saying that this magnetic field they've put around the fuel tank is strong enough to create a pressure similar to the weight of a star?" "Take a look at the chart," Richards said, pointing to the viewscreen. "If you know of any other type of substance with a density like that, I'll eat it." There was a brief conversation, then Dr. Bennett said, "All right, Pat. Is that all?" "Hell no," Richards said, his cat-like grin returning. "There's more." He tapped a button on the viewscreen control panel, and another chart came up on the screen. * * * * * "We know the power output of the generator. That was simply obtained, since the one unit powers all the machinery in the buildings out there. So we calculated all the known methods for obtaining power from a degenerate gas, and checked them against the amount of fuel the system has used up so far...." Lee interrupted. "How do you know how much fuel has been used if you can't get into the tank?" Richards' grin broadened. "Oh, that's easy, Dr. Lee. We know how much a degenerate gas should weigh, per unit volume. We know the size of the tank, and therefore how much it can hold, when full. So we can estimate how full the tank is simply by measuring its mass and comparing it to the mass it would have if it were full." "Doesn't the chemical composition of the gas have any effect on the mass? Wouldn't uranium be heavier than hydrogen?" "Yes, but not much. A factor of a hundred. You'll see in a minute that it's not enough to matter at this stage of the game." Lee nodded and the physicist went on. "Well, anyway, you can check out our math in the report we'll issue later this month. But it turns out that the only possible energy source for this gadget is total annihilation of the gas particles into energy." "Total annihilation? How?" "That's a good question. I don't think we'll be able to answer it until we can start taking the damned machine apart." He flicked a new graph on the screen. "But, we can calculate how long the thing has been running, on the basis of the fuel it's used up, and the energy rates we've assumed...." A slow wave of astonishment crept through the small room as, one by one, they grasped the significance of the curving lines on the graph. "That's right," Richards said. "Unless our rough calculations are completely off the beam, which I doubt, the damned thing has been operating continuously for something like ten-to-the-fifth or ten-to-the-sixth Earth years." A hundred thousand to a million years.