Evening was approaching and Lagrange I was low in the sky. It had been a bright day, reasonably warm, and Boris Vernadsky felt pleased. He had made interesting measurements and his brilliantly colored sweater had showed fascinating changes from hour to hour as the suns' positions shifted.

Right now his shadow was a long red thing, with the lowest third of it gray, where the Lagrange II shadow coincided. He held out one arm and it cast two shadows. There was a smeared orange one some fifteen feet away and a denser blue one in the same direction but only five feet away. If he had time, he could work out a beautiful set of shadowgrams.

He was so pleased with the thought that he felt no resentment at seeing Mark Annuncio skirting his trail in the distance.

He put down his nucleometer and waved his hand. "Come here!"

The youngster approached diffidently. "Hello."

"Want something?"

"Just-just watching."

"Oh? Well, go ahead and watch. Do you know what I'm doing?"

Mark shook his head.

"This is a nucleometer," said Vernadsky. "You jab it into the ground like this. It's got a force-field generator at the top so it will penetrate any rock." He leaned on the nucleometer as he spoke, and it went two feet into the stony outcropping. "See?"

Mark's eyes shone, and Vernadsky felt pleased. The chemist said, "Along the sides of the uniped are microscopic atomic furnaces, each of which vaporizes about a million molecules or so in the surrounding rock and decomposes them into atoms. The atoms are then differentiated in terms of nuclear mass and charge and the results may be read off directly on the dials above. Do you follow all that?"

"I'm not sure. But it's a good thing to know."

Vernadsky smiled and said, "We end up with figures on the different elements in the crust. It's pretty much the same on all oxygen-water planets."

Mark said seriously, "The planet with the most silicon I know of is Lepta, with 32.765 per cent. Earth is only 24.862. That's by weight."

Vernadsky's smile faded. He said dryly, "You have the figures on all the planets, pal?"

"Oh no. I couldn't I don't think they've all been surveyed. Bischoon and Spenglov's Handbook of Planetary Crusts only lists figures for 21,854 planets. I know all those, of course."

Vernadsky, with a definite feeling of deflation, said, "Now Junior has a more even distribution of elements than is usually met up with. Oxygen is low. So far my average is a lousy 42.113. So is silicon, with 22.722. The heavy metals are ten to a hundred times as concentrated as on Earth. That's not just a local phenomenon, either, since Junior's over-all density is 5 per cent higher than Earth's."

Vernadsky wasn't sure why he was telling the kid all this. Partly, he felt, because it was good to find someone who would listen. A man gets lonely and frustrated when there is no one of his own field to talk to.

He went on, beginning to relish the lecture. "On the other hand, the lighter elements are also better distributed. The ocean solids aren't predominantly sodium chloride, as on Earth. Junior's oceans contain a respectable helping of magnesium salts. And take what they call the "rare lights." Those are the elements lithium, beryllium, and boron. They're lighter than carbon, all of them, but they are of very rare occurrence on Earth, and in fact, on all planets. Junior, on the other hand, is quite rich in them. The three of them total almost four tenths of a per cent of the crust as compared to about four thousandths on Earth."

Mark plucked at the other's sleeve. "Do you have a list of figures on all the elements? May I see?"

"I suppose so." He took a folded piece of paper out of his hip pocket.

He grinned as Mark took the sheet and said, "Don't publish those figures before I do."

Mark glanced at them once and returned the paper.

"Are you through?" asked Vernadsky in surprise.

"Oh yes," said Mark thoughtfully, "I have it all." He turned on his heel and walked away with no word of parting.

The last glimmer of Lagrange I faded below the horizon.

Vernadsky gazed after Mark and shrugged. He plucked his nucleometer out of the ground, and followed after, walking back toward the tents.