"The liner has gone the way of the first two," he replied: "and the yarn about the pillar of fire was not so far wrong after all."

"You saw the same thing?" asked George incredulously.

"Yes, and so did Jack. There came some beams of light from the sky; then the pillar of fire and the roaring you heard, after which the vessels were gone and our electrical system paralyzed."

"Holy smoke!" e.j.a.c.u.l.a.t.ed George. "What to do now?"

As he spoke, the _Pioneer_ came out of the spin, and we were able to resume our positions in the seats. None of us was strapped in, and we had been clinging to whatever was handiest to keep from being tossed about in the cabin. Hart wiped his forehead and growled out an oath. The instrument board was still illuminated, for its tiny lamps were supplied with current from the storage battery. But the main lights of the cabin and the ignition system refused to function. We were gliding now, but losing alt.i.tude rapidly, having already dropped to the lower limits of level five.

"Can't you use the rocket tubes?" I inquired hesitatingly.

"They are fired in the same manner as the motor," replied Hart; "but we might try an emergency connection from the storage battery, which is ordinarily used only in starting and for the panel lights."

George was already fussing with the connections in a small junction box from which he had removed the cover. Meanwhile, the black waters of Lake Erie were rushing upward to meet us, and the needle of the altimeter registered twelve thousand feet.

"Here's the trouble!" shouted George, triumphantly holding up a small object he had removed from the junction box. "Ignition fuse is blown."

"Probably by some radiations from the cone of light and the column that destroyed the liner. Lucky we were no closer," were Hart's muttered comments.

George produced a spare fuse and inserted it in its proper place. The cabin lights glowed instantly and the motor started at once.

"Well, I'm going up after the generators of this mysterious force that is destroying our cross-country ships and killing our people," a.s.serted Hart. "The rays came from high above, but the _Pioneer_ can go as high as anything that ever flew--_higher_."

He snapped a switch and a beam of light that rivalled the so-called pillar of fire bored far into the night, dimming the stars by its brilliance. Again his fingers strayed to the rows of white keys and the rocket tubes shrieked in response to his pressure. This time I was prepared for the shock of acceleration, but the action was maintained for several seconds and I found the pressure against my back growing painful. Then it was relieved, and I glanced at the altimeter. Its needle had reached the end of the scale, which was graduated to eighty thousand feet!

"Good Lord!" I exclaimed. "Do you mean to tell me that we are more than sixteen miles in the air?"

"Nearly thirty," replied Hart, pointing to another dial which I had not seen. This one was graduated in miles above sea-level, and its needle wavered between the twenty-nine and thirty mark!

Again Hart pressed the rocket b.u.t.tons, and we shot still higher into the heavens. Thirty, forty, fifty miles registered the meter, and still we climbed.

"Great Scott!" blurted a voice I knew was my own, though I had no consciousness of willing the speech. "At this rate we'll reach the moon!"

"We could, if we wished," was Hart's astounding reply; "I wish you wouldn't say too much about it when we return. We have oxygen to breathe and an air-tight vessel to retain it. With the fuel we are using, we could easily do it, provided a sufficient supply were available.

However, the _Pioneer_ does not have large enough storage tanks as yet, and, of course, we cannot now replenish our supply with sufficient rapidity, for the atmosphere has become very rare indeed--where we are.

My ultimate object, though, in building the _Pioneer_, was to construct a vessel that is capable of a trip to the moon."

"You think you could reach a great enough velocity to escape the gravitational pull of the earth?" I asked, marveling more and more at the temerity and resourcefulness of my science-minded friend.

"Absolutely," he replied. "The speed required is less than seven miles a second, and I have calculated that the _Pioneer_ can do no less than twenty."

Mentally I multiplied by sixty. I could hardly credit the result. Twelve hundred miles a minute!

"But, how about the acceleration?" I ventured. "Could the human body stand up under the strain?"

"That is the one problem remaining," he replied; "and I am now working on a method of neutralizing it. From the latest results of our experiments, George and I are certain of its feasibility."

The _Pioneer_ was now losing alt.i.tude once more, and Hart played the beam of the searchlight in all directions as we descended. He and George watched through one of the floor ports and I followed suit. We were falling, unhampered by air resistance, and our bodies were practically weightless with reference to the _Pioneer_. It was a strange sensation: there was the feeling of exhilaration one experiences when inhaling the first whiff of nitrous oxide in the dentist's chair--a feeling of absolute detachment and care-free confidence in the ultimate result of our precipitous descent.

I found considerable amus.e.m.e.nt in pushing myself from side to side of the cabin with a mere touch of a finger. There was no up nor down, and sometimes it seemed to me that we were drifting sideways, sometimes that we fell upward rather than downward. Hart and George were unconcerned.

Evidently they were quite accustomed to the sensations. They bent their every energy toward discovering what had caused the disaster to the SF-22 and its convoy.

For several hours we cruised about on the strangest search ever made in the air. Alternately shooting skyward to unconscionable alt.i.tudes and dropping to levels five and six to replenish our fuel supply, we covered the greater portion of the United States before the night was over. But the powerful searchlight of the _Pioneer_ failed to disclose anything that might be remotely connected with the disappearance of the SF-22.

For me it was a never-to-be-forgotten experience. Lightning dashes from coast to coast which required but a few minutes of time--circling many miles above New York or Washington or Savannah in broad daylight with the sun low on the up-curved horizon; then shooting westward into the darkness and skirting the Pacific coast less than fifteen minutes later, but with four hours' actual time difference. s.p.a.ce and time were almost one.

Hart had not provided the _Pioneer_ with a radio or television transmitter, but there was an excellent receiver, and, through its agency we learned that the world was in a veritable uproar over the latest visitation of the mysterious terror of the sixth air level. All commercial traffic in levels four, five and six was ordered discontinued, and the government air control stations were flashing long messages in code, the import of which could but be guessed. Vision flashes showed immense gatherings at the large airports and in the public squares of the great cities, where the general populace become more and more excited and terrified by the awful possibilities pictured by various prominent speakers.

The governments of all foreign powers made haste to disclaim responsibility for the air attacks or for any attempt at making war on the United States. News broadcasts failed to mention Hart Jones or the _Pioneer_, since the mission had been kept secret. The phenomenon of the rays and the roaring column of light had been observed from many points on this occasion and there was no longer any doubt as to the nature of the terror as visible to the eye, though theories as to the action and source of the rays conflicted greatly and formed the basis of much heated discussion.

Eventually the advancing dawn reached San Francisco, and with its advent Hart decided to make a landing in that city so that my bonds could be delivered.

Jones was apparently a very much mystified and discouraged man. "Jack,"

he said, "it seems to me that this thing is but the beginning of some tremendous campaign that is being waged against our country by a clever and powerful enemy. And I feel that our work in connection with the unraveling of the mystery and overcoming the enemy or enemies is but begun. It's a cinch that the thing is organized by human minds and is not any sort of a freak of the elements. Our work is cut out for us, all right, and I wish you would stick to George and me through the mess.

Will you?"

"Sure," I agreed, readily enough. "After these bonds are delivered I am free for a month."

"Ha! Ha!" cackled George, without mirth. "A month! We're doggoned lucky if we get to the bottom of this in a year."

"Nonsense!" snapped Hart, who was considerably upset by the failure to locate the source of the disastrous rays. "There is nothing supernatural about this, and anything that can be explained on a scientific basis can be run to earth in short order. These rays are man-made and, as such, can be accounted for by man. Our greatest scientists must be put to work on the problem at once--in fact, they have quite probably been called in by the government already."

He was maneuvering the _Pioneer_ to a landing on the broad field of the San Francisco airport. Hundreds of idle planes of all sizes lined the field, and, unmindful of the earliness the hour, a great crowd was collected in expectation of sensational reports from the occupants of arriving ships. The unusual construction of the _Pioneer_ attracted considerable attention and it was with difficulty that the police kept back the crowd when she rolled to a stop near the office of the local government supervisor. We hustled inside and were greeted by that official with open arms.

"Glory be!" he exclaimed. "Hart Jones and the _Pioneer_. Every airport in the land has been on the lookout for you all night. It was feared you had been lost with the SF-22 and the others. Code messages to the supervisors of all districts advised of your mission, though it has been kept out of the general news, as has the message from the enemy."

"Message from the enemy!" gasped Hart, George and I, echoing the words like parrots.

"Yes. A demand that the United States surrender, and a threat to descend into the lower levels if the demand is not complied with in twenty-four hours!"

"Who is this enemy?" asked Hart, "and where?"

"Who they are is not known," replied the official gravely; "and as to the location, the War Department is puzzled. Direction finders throughout the country took readings on the position of their radio transmitter and these readings differed widely in result. But the consensus of opinion is that the messages originate somewhere out in s.p.a.ce, probably between fifty and one hundred thousand miles from our earth."

"Great guns!" Hart glanced at George and me, where we stood with stupidly hanging jaws. "And what does the government want of me now?"