The doctor, who was easily the most musical of the four men, sang in a cheerful baritone:
"The owl and the pussy-cat went to sea In a beautiful, pea-green boat."
The geologist, who had held down the lower end of a quartet in his university days, growled an accompaniment under his breath as he blithely peeled the potatoes. Occasionally a high-pitched note or two came from the direction of the engineer; he could not spare much wind while clambering about the machinery, oil-can in hand. The architect, alone, ignored the famous tune.
"What I can't understand, Smith," he insisted, "is how you draw the electricity from the ether into this car without blasting us all to cinders."
The engineer squinted through an opal glass shutter into one of the tunnels, through which the anti-gravitation current was pouring. "If you didn't know any more about buildings than you do about machinery, Jackson," he grunted, because of his squatting position, "I'd hate to live in one of your houses!"
The architect smiled grimly. "You're living in one of 'em right now, Smith," said he; "that is, if you call this car a house."
Smith straightened up. He was an unimportant-looking man, of medium height and build, and bearing a mild, good-humored expression. Nobody would ever look at him twice, would ever guess that his skull concealed an unusually complete knowledge of electricity, mechanisms, and such practical matters.
"I told you yesterday, Jackson," he said, "that the air surrounding the earth is chock full of electricity. And—"
"And that the higher we go, the more juice," added the other, remembering. "As much as to say that it is the atmosphere, then, that protects the earth from the surrounding voltage."
The engineer nodded. "Occasionally it breaks through, anyhow, in the form of lightning. Now, in order to control that current, and prevent it from turning this machine, and us, into ashes, all we do is to pass the juice through a cylinder of highly compressed air, fixed in this wall. By varying the pressure and dampness within the cylinder, we can regulate the flow."
The builder nodded rapidly. "All right. But why doesn't the electricity affect the walls themselves? I thought they were made of steel."
The engineer glanced through the dead-light at the reddish disk of the Earth, hazy and indistinct at a distance of forty million miles. "It isn't steel; it's a non-magnetic alloy. Besides, there's a layer of crystalline sulphur between the alloy and the vacuum space."
"The vacuum is what keeps out the cold, isn't it?" Jackson knew, but he asked in order to learn more.
"Keeps out the sun's heat, too. The outer shell is pretty blamed hot on that side, just as hot as it is cold on the shady side." Smith seated himself beside a huge electrical machine, a rotary converter which he next indicated with a jerk of his thumb. "But you don't want to forget that the juice outside is no use to us, the way it is. We have to change it.
"It's neither positive nor negative; it's just neutral. So we separate it into two parts; and all we have to do, when we want to get away from the earth or any other magnetic-sphere, is to aim a bunch of positive current at the corresponding pole of the planet, or negative current at the other pole. Like poles repel, you know."
"Listens easy," commented Jackson. "Too easy."
"Well, it isn't exactly as simple as all that. Takes a lot of apparatus, all told," and the engineer looked about the room, his glance resting fondly on his beloved machinery.
The big room, fifty feet square, was almost filled with machines; some reached nearly to the ceiling, the same distance above. In fact, the interior of the "cube," as that form of sky-car was known, had very little waste space. The living quarters of the four men who occupied it had to be fitted in wherever there happened to be room. The architect's own berth was sandwiched in between two huge dynamos.
He was thinking hard. "I see now why you have such a lot of adjustments for those tunnels," meaning the six square tubes which opened into the ether through the six walls of the room. "You've got to point the juice pretty accurately."
"I should say so." Smith led the way to a window, and the two shaded their eyes from the lights within while they gazed at the ashy glow of Mercury, toward which they were traveling. "I've got to adjust the current so as to point exactly toward his northern half." Smith might have added that a continual stream of repelling current was still directed toward the earth, and another toward the sun, away over to their right; both to prevent being drawn off their course.
"And how fast are we going?"
"Four or five times as fast as mother earth: between eighty and ninety miles per second. It's easy to get up speed out here, of course, where there's no air resistance."
Another voice broke in. The geologist had finished his potatoes, and a savory smell was already issuing from the frying pan. Years spent in the wilderness had made the geologist a good cook, and doubly welcome as a member of the expedition.
"We ought to get there tomorrow, then," he said eagerly. Indoor life did not appeal to him, even under such exciting circumstances. He peered at Mercury through his binoculars. "Beginning to show up fine now."
The builder improved upon Van Emmon's example by setting up the car's biggest telescope, a four-inch tube of unusual excellence. All three pronounced the planet, which was three-fourths "full" as they viewed it, as having pretty much the appearance of the moon.
"Wonder why there's always been so much mystery about Mercury?" pondered the architect invitingly. "Looks as though the big five-foot telescope on Mt. Wilson would have shown everything."
"Ask doc," suggested Smith, diplomatically. Jackson turned and hailed the little man on the other side of the car. He looked up absently from the scientific apparatus with which he had been making a test of the room's chemically purified air, then he stepped to the oxygen tanks and closed the flow a trifle, referring to his figures in the severely exact manner of his craft. He crossed to the group.
"Mercury is so close to the sun," he answered the architect's question, "he's always been hard to observe. For a long time the astronomers couldn't even agree that he always keeps the same face toward the sun, like the moon toward the earth."
"Then his day is as long as his year?"
"Eighty-eight of our days; yes."
"Continual sunlight! He can't be inhabited, then?" The architect knew very little about the planets. He had been included in the party because, along with his professional knowledge, he possessed remarkable ability as an amateur antiquarian. He knew as much about the doings of the ancients as the average man knows of baseball.
Dr. Kinney shook his head. "Not at present, certainly."
Instantly Jackson was alert. "Then perhaps there were people there at one time!"
"Why not?" the doctor put it lightly. "There's little or no atmosphere there now, of course, but that's not saying there never has been. Even if he is such a little planet—less than three thousand, smaller than the moon—he must have had plenty of air and water at one time, the same as the Earth."
"What's become of the air?" Van Emmon wanted to know. Kinney eyed him in reproach. He said:
"You ought to know. Mercury has only two-fifths as much gravitation as the earth; a man weighing a hundred and fifty back home would be only a sixty-pounder there. And you can't expect stuff as light as air to stay forever on a planet with no more pull than that, when the sun is on the job only thirty-six millions miles away."
"About a third as far as from the Earth to the sun," commented the engineer. "By George, it must be hot!"
"On the sunlit side, yes," said Kinney. "On the dark side it is as cold as space itself—four hundred and sixty below, Fahrenheit."
They considered this in silence for some minutes. The builder went to another window and looked at Venus, at that time about sixty million miles distant, on the far side of the sun. They were intending to visit "Earth's twin sister" on their return. After a while he came back to the group, ready with another question:
"If Mercury ever was inhabited, then his day wasn't as long as it is now, was it?"
"No," said the doctor. "In all probability he once had a day the same length as ours. Mercury is a comparatively old planet, you know; being smaller, he cooled off earlier than the earth, and has been more affected by the pull of the sun. But it's been a mighty long time since he had a day like ours; before the earth was cool enough to live on, probably."
"But since Mercury was made out of the same batch of material—" prompted the geologist.
"No reason, then, why life shouldn't have existed there in the past!" exclaimed the architect, his eyes sparkling with the instinct of the born antiquarian. He glanced up eagerly as the doctor coughed apologetically and said:
"Don't forget that, even if Mercury is part baked and part frozen, there must be a region in between which is neither." He picked up a small globe from the table and ran a finger completely around it from pole to pole. "So. There must be a narrow band of country where the sun is only partly above the horizon, and where the climate is temperate."
"Then—" the architect almost shouted in his excitement, an excitement only slightly greater than that of the other two—"then, if there were people on Mercury at one time—"
The doctor nodded gravely. "There may be some there now!"