But no one had an answer to that.

Van Emmon said he would give all he was worth to explore the Sanusian mountains long enough to learn their geology.  He said that the rocks ought to produce some new mineral forms, due to the peculiar condition of strain they would be subjected to.

“I’m not sure,” said he thoughtfully, “but I shouldn’t be surprised if there’s an enormous amount of carbon there.  Maybe diamonds are as plentiful as coal is here.”

At the word “diamonds” Smith glanced covertly at Billie’s left hand.  But she had hidden it in the folds of her skirt.  Next moment the doctor warned them to be quiet; Somat and Rolla were talking again.

He was telling her about his world.  She learned that his people, who had never concerned themselves with her side of the planet, had progressed enormously beyond the Sanusians.  Rolla did not understand all that he told her; but the people on the earth gathered, in one way or another, that civilization had proceeded about as far as that of the year 1915 in Europe.  All this, while fellow humans only a few thousand miles away, not only failed to make any progress at all, but lived on, century after century, the absolute slave of a race of bees!

But it was a fact.  The ancient city in which Rolla found herself had been, only a generation before, a flourishing metropolis, the capital of a powerful nation.  There had been two such nations on that side of the planet, and the most violent rivalry had existed between them.

“However,” Somat told Rolla, “’twas not this rivalry which wrought their downfall, except indirectly.  The last great war between them was terrible, but not disastrous.  Either could have survived that.

“But know you that the ruler of one of the nations, in order to carry on this war—­which was a war of commerce (never mind what that means)—­in order to carry it on was obliged to make great concessions to his people.  In the other nation, the ruler oppressed the workers, instead, and drove them mad with his cruelty.  So that, not long after the end of the war, there was a great rebellion among the people who had been so long oppressed, and their government was overthrown.”

Back on the earth the four investigators reflected on this in amazement.  The case was wonderfully like that of Russia after the great war.  Perhaps—­

“Immediately the other nation forced its soldiers to fight the victorious rebels.  But at home the workers had tasted of power.  Many refused to work at all; and one day, behold, there were two rebellions instead of one!  And within a very short time the whole world was governed by—­the working class!”

So this was what the Venusians had meant when they wrote that Sanus was ruled by the workers!

“What became of these rebellions?” Rolla asked, little understanding what it meant, but curious anyhow.