What was I to do? I had been depending upon Fal Sivas, and now he had failed me.

"I cannot understand you," I said; "with your own arguments, you convinced me that it would be a simple thing to go to Thuria in your ship. What possible danger can confront us there that we may not overcome? We shall be veritable giants on Thuria. No creature that lives there could withstand us. With the stamp of a foot, we could crush the lives from the greatest beasts that Thuria could support."

I had been giving this matter considerable thought ever since there first appeared a likelihood that I might go to Thuria. I am no scientist, and my figures may not be accurate, but they are approximately true. I knew that the diameter of Thuria was supposed to be about seven miles, so that its volume could be only about two percent of that of, let us say, the Earth, that you may have a comparison that will be more understandable to you.

I estimated that if there were human beings on Thuria and they were proportioned to their environment as man on Earth is to his, they would be but about nine-and-a-half inches tall and weigh between four and five pounds; and that an earth-man transported to Mars would be able to jump 225 feet into the air, make a standing broad jump of 450 feet and a running broad jump of 725 feet, and that a strong man could lift a mass equivalent to a weight of 4 tons on earth.

Against such a Titan, the tiny creatures of Thuria would be helpless— provided, of course, that Thuria were inhabited.

I suggested all this to Fal Sivas, but he shook his head impatiently. "There is something that you do not know," he said. "Perhaps Gar Nal, himself, does not know it. There is a peculiar relationship between Barsoom and her moons that does not exist between any of the other planets in the solar system and their satellites. The suggestion was made by an obscure scientist thousands of years ago, and then it seemed to have been forgotten. I discovered it in an ancient manuscript that I came upon by accident. It is in the original handwriting of the investigator and may have had no distribution whatsoever.

"However, the idea intrigued me; and over a period of twenty years I sought either to prove or disprove it. Eventually, I proved it conclusively."

"And what is it?" I asked.

"There exists between Barsoom and her satellites a peculiar relation which I have called a compensatory adjustment of masses. For example, let us consider a mass travelling from Barsoom to Thuria. As it approaches the nearer moon, it varies directly as the influences of the planet and the satellite vary. The ratio of the mass to the mass of Barsoom at the surface of Barsoom, therefore, would be the same as the ratio of the mass to the mass of Thuria, at the surface of Thuria.