Yet strange vicissitudes and changes are the portion of those who follow the sea; which may also be applied to other voyagers of space, the sailors of the air.  One minute all seems fair, with the sun shining; another, and a white squall is dashing down upon the ship, to catch the crew unawares and perhaps smother them with its mighty foam-crested billows.

It was not half an hour later when something happened that was calculated to chill the hearts of those bold navigators, such as even close contact to the ice-floe and berg could never bring about.

At the time they had reached a point almost above the field of ice from the Arctic regions, and Jack was scrutinizing its full extent, commenting the while on many peculiar features that attracted his attention.

“It’s a Polar bear, all right, fellows,” he announced, “and believe me he’s some size in the bargain.  If I had a rifle along I wouldn’t mind dropping down there and rustling him.  But what ails you, Tom?  You seem bothered about something.  Gee! you’re as white as a ghost!”

Lieutenant Beverly leaned forward and clutched the pilot’s arm.

“Anything gone wrong with the motors, Tom?” he demanded hoarsely.

“I’ve just made a terrible discovery,” replied Tom, trying to control himself.  “The worst has happened, and I’m afraid we’re in for a bad time!”

CHAPTER XIX

A DESPERATE CHANCE

“Tell us the worst, Tom!” cried Beverly hoarsely.

Jack tried to echo the words, but his tongue seemed to stick to the roof of his mouth.  He knew his chum well enough to feel assured that no ordinary hovering peril could cause the other to look so ashen pale.  It must be a frightful catastrophe by which they were threatened, Jack realized.

“The feed pipe!  It must be choking up!  Latterly I’ve more than suspected the motors were doing poorer work than before!”

The others understood.  Under ordinary conditions they would decide on dropping to the ground for repairs; a task that might be carried out in a brief time, or consume hours, everything depending on the condition in which they found things.

But how utterly impossible to dream of doing anything like that now!  Jack looked down to where, in the declining light of the sun, he could see that limitless sea of billowy water.  How different indeed all might be were their airship a seaplane, capable of floating on the surface of the water and making a successful launch from it, just as a gull would do.

“I’ll take a look, Tom!” Lieutenant Beverly called out.  “Not that I doubt what you say, but all of us will have to put our heads together; we shall need all our wits if what you fear proves to be a fact.”

Tom was more than willing, in fact he would have himself insisted on the lieutenant or Jack doing this very thing.  Pilots differ in plenty of ways; and, as Beverly had said, one might hit on an answer to the problem that had entirely escaped the others.