Robert paused and read the altimeter again. Eight thousand. He gripped the gyrostatic control, and carefully moved it to half speed.
The Sphere seemed to pause a moment, then they could detect its beginning to settle earthward as the neutralization of gravity was modified. Six thousand; five thousand; they were dropping steadily at a rate of nearly a thousand feet a minute.
Robert shoved the lever back to full speed and the Sphere’s downward momentum was quickly checked. With the disk safely throttled, the Sphere became as a rubber balloon. They merely drifted in midair.
Together they peered through the observation well in the floor. Through this they could plainly see the landscape, some three thousand feet below, sliding by sluggishly as they drifted with the light air current. From the side ports they could discern the big Palmer homestead and the laboratories about a mile and a half to the west of them. It was an ideal day for observation. The sky was cloudless, and the air of crystal clearness.
“Well, professor, shall we run back to our stall, or take a little sight-seeing jaunt?” queried Robert.
“Let’s see some of the country, by all means,” decided the professor, his face aglow with boyish excitement and anticipation.
“All right; here goes,” Robert sang out as he deflected the disk to a horizontal position, pointing due north.
The next instant he switched open the first shutter from the disk’s surface. There was a jerk, and the landscape suddenly began slipping away to the south with accelerating speed. Another click, and their speed was further increased. Once more the switch clicked, releasing the last shutter from over the disk. The Sphere seemed literally to leap ahead. A muffled roar without indicated the great speed at which they were rushing through the air.
Town after town flashed by beneath them with astonishing rapidity. The fact that they were flying at a comparatively low altitude made their speed seem terrific. Robert wisely decided to seek a safer height. He elevated the disk several degrees and the Sphere promptly soared higher. At eight thousand feet he checked its upward trend.
Far away to the east they could see a solitary big biplane bound in the same direction as they—probably a fast mail express; but it was quickly left behind, and lost from view in the afternoon haze.