compressed it to about 600 atmospheres. There is no better shield against high-energy neutrons; they bounce off the light molecules and slow down to a speed which makes them perfectly harmless laggards which don't travel far before decaying into hydrogen themselves. This, as well as the direct radiation of the pile, turned the room hot—some 500 degrees.

So what was more natural than that the same hydrogen should be circulated through pipes of chrome-vanadium steel, which is relatively impenetrable even at such temperatures, and heat the domes?

There was, of course, considerable loss of energy as the compressed gas seeped through the Hill and back into the satellite's atmosphere. But the pumps maintained the pressure. It was not the most efficient system which could have been devised; it would have been ludicrous on Earth. But on Triton, terminal of nowhere, men had necessarily sacrificed some engineering excellence to the stiff requirements of transportation and labor.

And after all, it had worked without a hitch for many years on Saturn's largest moon. It had worked for two years on Neptune's—

Samuel Vesey drummed on his desk with nervous fingers. His dark countenance was already haggard, the eyes sunken and feverish.

"Yes," he said. "Yes, it was news to me."

Jahangir put down the counter. The office was very quiet for a while.

"Don't spread the word," said Vesey. "We'll confine it to the engineers. Conditions are bad enough without a riot breaking loose. We can take several days of this radiation without harm, but you know how some people are about it."

"You've not been very candid so far," snapped Catherine. "Just exactly what have you learned?"

Jahangir shrugged. There was a white frost rimming his beard. "There've been no bulletins because there's no news," he replied. "We checked the pile. It's still putting out as it should. The neutron flux density is the same as ever. It's the gas there and in our pipes which has gotten cold and ... radioactive."

"Have you looked directly in the pile room—actually entered?" demanded Alemán.

Jahangir lifted his shoulders again. "My dear old chap," he murmured. "At a temperature of 500 and a pressure of 600?" After a moment, he frowned. "I do have some men modifying a trac so it could be driven in 

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