But it was only for a few minutes that they were in the worst danger. Soon, to their infinite relief, they had reached their "ceiling."  They were now 15,000 feet up--almost three miles,--and below them lay the vast sea of troubled cloudland, dark and forbidding, rolling tumultuously like an ocean of curdled ink.  It was a novel experience to be running in the clear air over all of this infernality of sounds and sights, while above them the blue, star-studded heavens looked down upon them calmly and peaceably.