The first steps were cautious enough. Slow enough, too. Cimon inspected his photochromes of Junior as taken from space with minute care. Under protest, he passed them among the others of the expedition, and more than a few groaned inwardly at the thought of having placed comfort before a chance to see the original of that.

Boris Vernadsky bent over his gas analyzer interminably, a symphony in loud clothes and soft grunts.

"We're about at sea level, I should judge," he said, "going by the value of g."

Then, because he was explaining himself to the rest of the group, he added negligently. "The gravitational constant, that is," which didn't help most of them.

He said, "The atmospheric pressure is just about eight hundred millimeters of mercury, which is about 5 per cent higher than on earth. And two hundred forty millimeters of that is oxygen as compared to only one hundred fifty on Earth. Not bad."

He seemed to be waiting for approval, but scientists found it best to comment as little as possible on data in another man's specialty.

He went on, "Nitrogen, of course. Dull, isn't it, the way nature repeats itself like a three-year-old who knows three lessons, period. Takes the fun away when it turns out that a water world always has an oxygen-nitrogen atmosphere. Makes the whole thing yawn-worthy."

"What else in the atmosphere?" asked Cimon irritably. "So far all we have is oxygen, nitrogen, and homely philosophy from kindly Uncle Boris."

Vernadsky hooked his arm over his seat and said, amiably enough, "What are you? Director or something?"

Cimon, to whom the directorship meant little more than the annoyance of preparing composite reports for the Bureau, flushed and said grimly, "What else in the atmosphere, Dr. Vernadsky?"

Vernadsky said, without looking at his notes, "Under 1 per cent and over a hundredth of 1 per cent: hydrogen, helium, and carbon dioxide in that order. Under a hundredth of 1 per cent and over a ten thousandth of 1 per cent: methane, argon, and neon in that order. Under a ten thousandth of 1 per cent and over a millionth of a per cent: radon, krypton, and xenon in that order.

"The figures aren't very informative. About all I can get out of them is that Junior is going to be a happy hunting ground for uranium, that it's low in potassium, and that it's no wonder it's such a lovely little double icecap of a world."

He did that deliberately, so that someone could ask him how he knew, and someone, with gratifying wonder, inevitably did.

Vernadsky smiled blandly and said, "Atmospheric radon is ten to a hundred times as high here as on Earth. So is helium. Both radon and helium are produced as by-products of the radioactive breakdown of uranium and thorium. Conclusion: Uranium and thorium minerals are ten to a hundred times as copious in Junior's crust as in Earth's.

"Argon, on the other hand, is over a hundred times as low as on Earth. Chances are Junior has none of the argon it originally started with. A planet of this type has only the argon which forms from the breakdown of K40, one of the potassium isotopes. Low argon; low potassium. Simple, kids."

One of the assembled groups asked. "What about the icecaps?"

Cimon, who knew the answer to that, asked, before Vernadsky could answer the other, "What's the carbon dioxide content exactly?"

"Zero point zero one six em em," said Vernadsky.

Cimon nodded, and vouchsafed nothing more.

"Well?" asked the inquirer impatiently.

"Carbon dioxide is only about half what it is on Earth, and it's the carbon dioxide that gives the hothouse effect. It lets the short waves of sunlight pass through to the planet's surface, but doesn't allow the long waves of planetary heat to radiate off. When carbon dioxide concentration goes up as a result of volcanic action, the planet heats up a bit and you have a carboniferous age, with oceans high and land surface at a minimum. When carbon dioxide goes down as a result of vegetation refusing to let a good thing alone, fattening up on the good old CO2 and losing its head about it, temperature drops, ice forms, a vicious cycle of glaciation starts, and voila-"

"Anything else in the atmosphere?" asked Cimon.

"Water vapor and dust. I suppose there are a few million air-borne spores of various virulent diseases per cubic centimeter in addition to that." He said it lightly enough, but there was a stir in the room. More than one of the bystanders looked as though he were holding his breath.

Vernadsky shrugged and said, "Don't worry about it for now. My analyzer washes out dust and spores quite thoroughly. But then, that's not my angle. I suggest Rodriguez grow his damn cultures under glass right away. Good thick glass."