Dunark can, for long," and Seaton dashed toward the vessel, motioning the visitor back.

But misunderstanding the signal, Dunark came on. As he clambered heavily through the door he staggered as though under an enormous weight, and Sitar collapsed upon the frozen ground. Trying to help her, half-kneeling over her, Dunark struggled, his green skin paling to a yellowish tinge at the touch of the bitter and unexpected cold. Seaton leaped forward and gathered Sitar up in his mighty arms as though she were a child.

"Help Dunark back in, Mart," he directed crisply. "Hop in, girls—we've got to take these folks back up where they can live."

Seaton shut the door, and as everyone lay flat in the seats Crane, who had taken the controls, applied one notch of power and the huge vessel leaped upward. Miles of altitude were gained before Crane brought the cruiser to a stop and locked her in place with an anchoring attractor.

"There," he remarked calmly, "gravitation here is approximately the same as it is upon Osnome."

"Yes," put in Seaton, standing up and shedding clothing in all directions, "and I rise to remark that we'd better undress as far as the law allows—perhaps farther. I never did like Osnomian ideas of comfortable warmth, but we can endure it by peeling down to bedrock——"

Sitar jumped up happily, completely restored, and the three women threw their arms around each other.

"What a horrible, terrible, frightful world!" exclaimed Sitar, her eyes widening as she thought of her first experience with our earth. "Much as I love you, I shall never dare try to visit you again. I have never been able to understand why you Terrestrials wear what you call 'clothes,' nor why you are so terribly, brutally strong. Now I really know—I will feel the utterly cold and savage embrace of that awful earth of yours as long as I live!"

"Oh, it's not so bad, Sitar." Seaton, who was shaking both of Dunark's hands vigorously, assured her over his shoulder. "All depends on where you were raised. We like it that way, and Osnome gives us the pip. But you poor fish," turning again to Dunark, "with all my brains inside your skull, you should have known what you were letting yourself in for."

"That's true, after a fashion," Dunark admitted, "but your brain told me that Washington was hot. If I'd have thought to recalculate your actual Fahrenheit degrees into our loro ... but that figures only forty-seven and, while very cold, we could have endured it—wait a minute, I'm getting it. You have what you call 'seasons.' This, then, must be your 'winter.' Right?"

"Right the first time. That's the way your brain works behind my pan, too. I could figure anything out all right after it happened, but hardly ever beforehand—so I guess I can't blame you much, at that. But what I want to know is, how'd you get here? It would take more than my brains—you can't see our sun from anywhere near Osnome, even if you knew exactly where to look for it."

"Easy. Remember those wrecked instruments you threw out of Skylark I when we built Skylark II?" Having every minute detail of the configuration of Seaton's brain engraved upon his own, Dunark spoke English in Seaton's own characteristic careless fashion. Only when thinking deeply or discussing abstruse matter did Seaton employ the carefully selected and precise phrasing, which he knew so well how to use. "Well, none of them was beyond repair and the juice was still on most of them. One was an object-compass bearing on the Earth. We simply fixed the bearings, put on some minor improvements, and here we are."

"Let us all sit down and be comfortable," he continued, changing into the Kondalian tongue without a break, "and I will explain why we have come. We are in most desperate need of two things which you alone can supply—salt, and that strange metal, 'X'. Salt I know you have in great abundance, but I know that you have very little of the metal. You have only the one compass upon that planet?"

"That's all—one is all we set on it. However, we've got close to half a ton of the metal on hand—you can have all you want."

"Even if I took it all, which I would not like to do, that would be less than half enough. We must have at least one of your tons, and two tons would be better."

"Two tons! Holy cat! Are you going to plate a fleet of battle cruisers?"

"More than that. We must plate an area of copper of some ten thousand square miles—in fact, the very life of our entire race depends upon it."

"It's this way," he continued, as the four earth-beings stared at him in wonder. "Shortly after you left Osnome we were invaded by the inhabitants of the third planet of our fourteenth sun. Luckily for us they landed upon Mardonale, and in less than two days there was not a single Osnomian left alive upon that half of the planet. They wiped out our grand fleet in one brief engagement, and it was only the Kondal and a few more like her that enabled us to keep them from crossing the ocean. Even with our full force of these vessels, we cannot defeat them. Our regular Kondalian weapons were useless. We shot explosive copper charges against them of such size as to cause earthquakes all over Osnome, without seriously crippling their defenses. Their offensive weapons are almost irresistible—they have generators that burn arenak as though it were so much paper, and a series of deadly frequencies against which only a copper-driven ray screen is effective, and even that does not stand up long."

"How come you lasted till now, then?" asked Seaton.

"They have nothing like the Skylark, and no knowledge of intra-atomic energy. Therefore their space-ships are of the rocket type, and for that reason they can cross only at the exact time of conjunction, or whatever you call it—no, not conjunction, exactly, either, since the two planets do not revolve around the same sun: but when they are closest together. Our solar system is so complex, you know, that unless the trips are timed exactly, to the hour, the vessels will not be able to land upon Osnome, but will be drawn aside and be lost, if not actually drawn into the vast central sun. Although it may not have occurred to you, a little reflection will show that the inhabitants of all the central planets, such as Osnome, must perforce be absolutely ignorant of astronomy, and of all the wonders of outer space. Before your coming we knew nothing beyond our own solar system, and very little of that. We knew of the existence of only such of the closest planets as were brilliant enough to be seen in our continuous sunlight, and they were few. Immediately after your coming I gave your knowledge of astronomy to a group of our foremost physicists and mathematicians, and they have been working ceaselessly from space-ships—close enough so that observations could be recalculated to Osnome, and yet far enough away to afford perfect 'seeing,' as you call it."

"But I don't know any more about astronomy than a pig does about Sunday," protested Seaton.

"Your knowledge of details is, of course, incomplete," conceded Dunark, "but the detailed knowledge of the best of your Earthly astronomers would not help us a great deal, since we are so far removed from you in space. You, however, have a very clear and solid knowledge of the fundamentals of the science, and that is what we need, above all things."

"Well, maybe you're right, at that. I do know the general theory of the motions, and I studied some Celestial Mechanics. I'm awfully weak on advanced theory, though, as you'll find out when you get that far."

"Perhaps—but since our enemies have no knowledge of astronomy whatever, it is not surprising that their rocket-ships can be launched only at one particularly favorable time; for there are many planets and satellites, of which they can know nothing, to throw their vessels off the course.

"Some material essential to the operation of their war