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.

"You were about right in assuming that an inhabitant of Thuria, if such exists, if he were of the same proportion to Thuria as you are to Barsoom, would be about eight sofs tall; and consequently, if my theory is correct, and I have no reason to doubt it, were you to travel from Barsoom to Thuria you would be but eight sofs tall when you reached the surface of the moon."

"Preposterous!" I exclaimed.

He flushed angrily. "You are nothing but an ignorant assassin," he cried. "How dare you question the knowledge of Fal Sivas? But enough of this; return to your quarters. I must get on with my work."

"I am going to Thuria," I said; "and if you won't go with me, I shall go alone."

He had turned back to enter his little laboratory, but I had followed him and was close behind him.

"Go away from here," he said; "keep out, or I will have you killed."

Just then I heard a cry from the room behind him, and a woman's voice calling, "Vandor! Vandor, save me!"

Fal Sivas went livid and tried to dash into the room and close the door in my face, but I was too quick for him. I leaped to the door and pushed him aside as I stepped in.

A terrible sight met my eyes. On marble slabs, raised about four feet from the floor, several women were securely strapped, so that they could not move a limb or raise their heads. There were four of them. Portions of the skulls of three had been removed, but they were still conscious. I could see their frightened, horrified eyes turn toward us.

I turned upon Fal Sivas. "What is the meaning of this?" I cried. "What hellish business are you up to?"

"Get out! Get out!" he screamed. "How dare you invade the holy precincts of science? Who are you, dog, worm, to question what Fal Sivas does; to interfere with the work of a brain the magnitude of which you cannot conceive? Get out! Get out! or I will have you killed."

"And who will kill me?" I demanded. "Put these poor creatures out of their misery, and then I will attend to you."

So great was either his rage or his terror, or both, that he trembled all over like a man with the palsy; and then, before I could stop him, he turned and darted from the room.

I knew that he had gone for help; that presently I should probably have all the inmates of his hellish abode upon me.

I might have pursued him, but I was afraid that something might happen here while I was gone, and so I turned back to the girl on the fourth slab. It was Zanda.

I stepped quickly to her side. I saw that she had not yet been subjected to Fal Sivas's horrid operation, and drawing my dagger I cut the bonds that held her.

She slipped from the table and threw her arms about my neck. "Oh, Vandor, Vandor," she cried, "now we must both die. They come! I hear them."

CHAPTER XIII. PURSUED

Heralding the approach of armed men was the clank of metal on metal. How many were coming, I did not know; but here I was with only my own sword between me and death and my back against the wall.

Zanda was without hope, but she remained cool and did not lose her head. In those few brief moments I could see that she was courageous.

"Give me your dagger, Vandor," she said.

"Why?" I asked.

"They will kill you, but Fal Sivas shall not have me nor these others to torture further."

"I am not dead, yet," I reminded her.

"I shall not kill myself until you are dead; but these others, there is no hope for them. They pray for merciful death. Let me put them out of their misery."

I winced at the thought, but I knew that she was right, and I handed her my dagger. It was a thing that I should have had to have done myself. It took much more courage than facing armed men, and I was glad to be relieved of the ghastly job.

Zanda was behind me now. I could not see what she was doing, and I never asked her what she did.

Our enemies had paused in the outer room. I could hear them whispering together.

Then Fal Sivas raised his voice and shouted to me.

"Come out of there and give yourself up," he screamed, "or we will come in and kill you."

I did not reply; I just stood there, waiting. Presently Zanda came close to me and whispered, "There is a door on the opposite side of this room, hidden behind a large screen. If you wait here, Fal Sivas will send men to that door; and they will attack you from in front and behind."

"I shall not wait, then," I said, moving toward the door leading into the outer room where I had heard my enemies whispering.

Zanda laid a hand upon my arm, "Just a moment, Vandor," she said. "You remain where you are, facing the door; and I will go to it and swing it open suddenly. Then they cannot take you by surprise, as they could if you were to open it."

The door was hinged so that it swung in, and thus Zanda would be protected as she drew it inward and stepped behind it.

Zanda stepped forward and grasped the handle while I stood directly in front of the door and a few paces from it, my long sword in my hand.

As she opened the door, a sword flashed inward in a terrific cut that would have split my skull had I been there.

The man who wielded the sword was Hamas. Just behind him, I saw Phystal and another armed man, while in the rear was Fal Sivas.

Now the old inventor commenced to scream at them and urge them on; but they held back, for only one man could pass through the doorway at a time; and none of them seemed to relish the idea of being the first. In fact, Hamas had leaped back immediately following his cut; and now his voice joined with that of Fal Sivas in exhorting the other two to enter the laboratory and destroy me.

"On, men!" cried Hamas. "We are three, and he is only one. Onward, you, Phystal! Kill the calot!"

"In with you, yourself, Hamas," growled Phystal.

"Go in! Go in and get him!" shrieked Fal Sivas. "Go in, you cowards." But no one came in; they just stood there, each urging the other to be first.

I did not relish this waste of time, and for two reasons. In the first place, I could not abide the thought of even a moment's unnecessary delay in starting out upon my quest for Dejah Thoris; and, secondly, there was always the danger that reinforcements might arrive. Therefore, if they would not come in to me, I would have to go out to them.

And I did go out to them, and so suddenly that it threw them into confusion.

Hamas and Phystal, in their efforts to avoid me, fell back upon the man behind them. He was only a slave, but he was a brave man-the bravest of the four that faced me.