speed was sinking very slowly, for the area of the absorbing fins was
not designed to absorb the sun's heat directly, and was very
inefficient. The sun was indeed sinking below their horizon; they were
just beginning to watch that curious phenomenon of seeing dawn backward,
when they first struck air dense enough to operate the power units
noticeably. Quickly the power was applied till the machines sank rapidly
to the warmer levels, the only governing factor being the tendency of
the glider to break loose from the grip of the magnet.

At fifty miles the generator was started, and the heaters in the car at
once became more active. There was no heat in the car below, but that
was unavoidable. They would try to bring it down to warm levels quickly.

"Whew, I'm glad we reached the air again, Dick. I didn't tell you
sooner, for it wouldn't have done any good, but that battery was about
gone! We had something like twenty amp-hours left! I'm giving the
recharge generator all she will take. We seem to have plenty of power
now."

"I knew the cells were low, but I had no idea they were as low as that!
I noticed that the magnet was weakening, but thought it was due to the
added air strain. I am going to put the thing into a nose dive and let
the glider go down itself. I know it would land correctly if it had a
chance. I am going to follow it, of course, and since we are over the
middle of Siberia we'd better start back."

The return trip was necessarily in the lower level of the atmosphere,
that the glider might be kept reasonably warm. At a height of but two
miles, in the turbulent atmosphere, the glider was brought slowly home.
It took them nearly twenty hours to go the short distance of twelve
thousand miles to San Francisco, the two men taking turns at the
controls. The air resistance of the glider forced them to go slowly;
they could not average much better than six hundred an hour despite the
fact that the speed of either machine alone was over twelve hundred
miles an hour.

At last the great skyscrapers of San Francisco appeared on their
horizon, and thousands of private planes started out to meet them.
Frantically Arcot warned them away, lest the air blast from their props
tear the glider from the magnet. At last, however, the Air Guard was
able to force them to a safe distance and clear a lane through one of
the lower levels of the city traffic. The great field of the
Transcontinental lines was packed with excited me