, and finally, at a height of
fifteen thousand feet--the greatest height they had yet attained--they
went over them. The airplane encountered several "air pockets" in this
process, which might have been disastrous to them except for the
stabilizing effect of the automatic-pilot. As it was, the machine
pitched rather roughly in surviving them.

In sweeping past the last crag they had come very near to striking,
owing to a cloud which enwrapped it. Just in time Paul's sharp eyes
had seen the white bank of snow on the crag ahead, and he elevated his
craft enough to pass over. It was so cold up here, even in the cabin,
that the boys had to don their heavy coats.

Just as they turned the nose of their machine toward a lower level,
running at reduced speed, a huge bird with curving beak, which John
said was a condor, dashed from the crags after the airplane. It was
followed a moment later by five or six others. The great birds seemed
to resent the appearance of so strange a giant in the mountain
fastnesses where they had always held the supremacy of the air, all the
time darting angrily at it, flapping their long, black and white wings,
some of which had the immense span of fourteen feet, and croaking
hoarsely.

The boys laughed at first, but when the creatures commenced to come
closer, frequently hitting the windows with their sharp beaks, and
cracking two of them, they began to get really alarmed. Once the
propeller struck the tail of one bold and incautious condor, and
feathers flew in all directions; but after a quick circle he was back
again, madder than ever.

"Say, fellows," cried Paul; "we've got to do something with these birds
right away! First thing we know, one of them will get hit a squarer
blow with the propeller and smash it. Then we'll crash as sure as I'm
sitting here."

This peril was very imminent, as all could see.

John seized the shot-gun from its rack, and Tom one of the rifles.
These were loaded. Stationing themselves on either side of the cabin,
the young men drew down the windows in front of them, poked out their
weapons and watched for a chance to use them.

Tom's gun was the first to blaze away, but it is difficult to hit a
bird on the wing with a rifle, and he missed. A moment later, as a
condor dashed viciously toward his window, John fired, and the great
bird, mortally stricken, tumbled into the mists below.

Tom was more fortunate the next time. A condor, with a fluttering