Fal Sivas reached up and laid a hand almost affectionately upon the spherical object to which he had called my attention. "This," he said, "is the brain."

Then he called my attention to two spots, one in the exact center of each crystal of the forward ports. I had not noticed them at first, but now I saw that they were ground differently from the balance of the crystals.

"These lenses," explained Fal Sivas, "focus upon this aperture in the lower part of the brain," and he called my attention to a small hole at the base of the sphere, "that they may transmit to the brain what the eyes of the ship see. The brain then functions mechanically precisely as the human brain does, except with greater accuracy."

"It is incredible!" I exclaimed.

"But, nevertheless, true," he replied. "In one respect, however, the brain lacks human power. It cannot originate thoughts. Perhaps that is just as well, for could it, I might have loosed upon myself and Barsoom an insensate monster that could wreak incalculable havoc before it could be destroyed, for this ship is equipped with high-power radium rifles which the brain has the power to discharge with far more deadly accuracy than may be achieved by man."

"I saw no rifles," I said.

"No," he replied. "They are encased in the bulkheads, and nothing of them is visible except small round holes in the hull of the ship. But, as I was saying, the one weakness of the mechanical brain is the very thing that makes it so effective for the use of man. Before it can function, it must be charged by human thought-waves. In other words, I must project into the mechanism the originating thoughts that are the food for its functioning.

"For example, I charge it with the thought that it is to rise straight up ten feet, pause there for a couple of seconds, and then come to rest again upon its scaffolding.

"To carry the idea into a more complex domain, I might impart to it the actuating thought that it is to travel to Thuria, seek a suitable landing place, and come to the ground. I could carry this idea even further, warning it that if it were attacked it should repel its enemies with rifle fire and maneuver so as to avoid disaster, returning immediately to Barsoom, rather than suffer destruction.

"It is also equipped with cameras, with which I could instruct it to take pictures while it was on the surface of Thuria."

"And you think it will do these things, Fal Sivas?" I asked.

He growled at me impatiently. "Of course it will. Just a few more days and I will have the last detail perfected. It is a minor matter of motor gearing with which I am not wholly satisfied."

"Perhaps I can help you there," I said. "I have learned several tricks in gearing during my long life in the air."

He became immediately interested and directed me to return to the floor of his hangar. He followed me down, and presently we were pouring over the drawings of his motor.