The broad tires of these unique fliers are but rubber-like gas bags filled with the eighth Barsoomian ray, or ray of propulsion-that remarkable discovery of the Martians that has made possible the great fleets of mighty airships that render the red man of the outer world supreme. It is this ray which propels the inherent or reflected light of the planet off into space, and when confined gives to the Martian craft their airy buoyancy.

The ground fliers of Marentina contain just sufficient buoyancy in their automobile-like wheels to give the cars traction for steering purposes; and though the hind wheels are geared to the engine, and aid in driving the machine, the bulk of this work is carried by a small propeller at the stern.

I know of no more delightful sensation than that of riding in one of these luxuriously appointed cars which skim, light and airy as feathers, along the soft, mossy avenues of Marentina. They move with absolute noiselessness between borders of crimson sward and beneath arching trees gorgeous with the wondrous blooms that mark so many of the highly cultivated varieties of Barsoomian vegetation.

By the end of the third day the court barber-I can think of no other earthly appellation by which to describe him-had wrought so remarkable a transformation in both Thuvan Dihn and myself that our own wives would never have known us. Our skins were of the same lemon color as his own, and great, black beards and mustaches had been deftly affixed to our smooth faces. The trappings of warriors of Okar aided in the deception; and for wear beyond the hothouse cities we each had suits of the black– and yellow-striped orluk.

Talu gave us careful directions for the journey to Kadabra, the capital city of the Okar nation, which is the racial name of the yellow men. This good friend even accompanied us part way, and then, promising to aid us in any way that he found possible, bade us adieu.

On parting he slipped upon my finger a curiously wrought ring set with a dead-black, lusterless stone, which appeared more like a bit of bituminous coal than the priceless Barsoomian gem which in reality it is.

"There had been but three others cut from the mother stone," he said, "which is in my possession. These three are worn by nobles high in my confidence, all of whom have been sent on secret missions to the court of Salensus Oll.

"Should you come within fifty feet of any of these three you will feel a rapid, pricking sensation in the finger upon which you wear this ring. He who wears one of its mates will experience the same feeling; it is caused by an electrical action that takes place the moment two of these gems cut from the same mother stone come within the radius of each other's power. By it you will know that a friend is at hand upon whom you may depend for assistance in time of need.

"Should another wearer of one of these gems call upon you for aid do not deny him, and should death threaten you swallow the ring rather than let it fall into the hands of enemies. Guard it with your life, John Carter, for some day it may mean more than life to you."

With this parting admonition our good friend turned back toward Marentina, and we set our faces in the direction of the city of Kadabra and the court of Salensus Oll, Jeddak of Jeddaks.

That very evening we came within sight of the walled and glass-roofed city of Kadabra. It lies in a low depression near the pole, surrounded by rocky, snow-clad hills. From the pass through which we entered the valley we had a splendid view of this great city of the north. Its crystal domes sparkled in the brilliant sunlight gleaming above the frost-covered outer wall that circles the entire one hundred miles of its circumference.

At regular intervals great gates give entrance to the city; but even at the distance from which we looked upon the massive pile we could see that all were closed, and, in accordance with Talu's suggestion, we deferred attempting to enter the city until the following morning.

As he had said, we found numerous caves in the hillsides about us, and into one of these we crept for the night. Our warm orluk skins kept us perfectly comfortable, and it was only after a most refreshing sleep that we awoke shortly after daylight on the following morning.

Already the city was astir, and from several of the gates we saw parties of yellow men emerging. Following closely each detail of the instructions given us by our good friend of Marentina, we remained concealed for several hours until one party of some half dozen warriors had passed along the trail below our hiding place and entered the hills by way of the pass along which we had come the previous evening.

After giving them time to get well out of sight of our cave, Thuvan Dihn and I crept out and followed them, overtaking them when they were well into the hills.

When we had come almost to them I called aloud to their leader, when the whole party halted and turned toward us. The crucial test had come. Could we but deceive these men the rest would be comparatively easy.

"Kaor!" I cried as I came closer to them.

"Kaor!" responded the officer in charge of the party.

"We be from Illall," I continued, giving the name of the most remote city of Okar, which has little or no intercourse with Kadabra. "Only yesterday we arrived, and this morning the captain of the gate told us that you were setting out to hunt orluks, which is a sport we do not find in our own neighborhood. We have hastened after you to pray that you allow us to accompany you."

The officer was entirely deceived, and graciously permitted us to go with them for the day. The chance guess that they were bound upon an orluk hunt proved correct, and Talu had said that the chances were ten to one that such would be the mission of any party leaving Kadabra by the pass through which we entered the valley, since that way leads directly to the vast plains frequented by this elephantine beast of prey.

In so far as the hunt was concerned, the day was a failure, for we did not see a single orluk; but this proved more than fortunate for us, since the yellow men were so chagrined by their misfortune that they would not enter the city by the same gate by which they had left it in the morning, as it seemed that they had made great boasts to the captain of that gate about their skill at this dangerous sport.

We, therefore, approached Kadabra at a point several miles from that at which the party had quitted it in the morning, and so were relieved of the danger of embarrassing questions and explanations on the part of the gate captain, whom we had said had directed us to this particular hunting party.

We had come quite close to the city when my attention was attracted toward a tall, black shaft that reared its head several hundred feet into the air from what appeared to be a tangled mass of junk or wreckage, now partially snow-covered.

I did not dare venture an inquiry for fear of arousing suspicion by evident ignorance of something which as a yellow man I should have known; but before we reached the city gate I was to learn the purpose of that grim shaft and the meaning of the mighty accumulation beneath it.

We had come almost to the gate when one of the party called to his fellows, at the same time pointing toward the distant southern horizon. Following the direction he indicated, my eyes descried the hull of a large flier approaching rapidly from above the crest of the encircling hills.

"Still other fools who would solve the mysteries of the forbidden north," said the officer, half to himself. "Will they never cease their fatal curiosity?"

"Let us hope not," answered one of the warriors, "for then what should we do for slaves and sport?"

"True; but what stupid beasts they are to continue to come to a region from whence none of them ever has returned."

"Let us tarry and watch the end of this one," suggested one of the men.