It had begun to cloud up a little and this made it darker than ever.  After following the turn-pike for nearly two miles, Sam veered slightly to catch the railroad tracks and the gleam of the signal lights.

“I can follow the lights best of all!” he shouted, into Dick’s ear.  “It’s too dark to see the road.”

“All right, follow the railroad right to Ashton,” answered the oldest Rover boy, naming the town that was the railroad station for Brill College.

The cloudiness increased rapidly, and long before Ashton was gained it commenced to blow, gently at first, and then stronger and stronger.  Evidently a storm was in the air.

“We are going to catch it!” was Tom’s comment.

“Oh, I don’t think it will storm just yet,” returned Sam.

“Watch yourself, Sam!” cried Dick, warningly.  “If the wind gets too strong bring her down in the first field we come to.”

“I will,” was the answer.

They were now flying close to the railroad tracks.  Presently they saw a glare of light illuminate the rails and a long line of freight cars, drawn by a big locomotive, passed beneath them.

“Wish that was going our way—­ we could follow it with ease,” said Sam, as the train disappeared from view, leaving the landscape below darker than ever.

The youngest Rover boy now had to give the Dartaway all of his attention.  The breeze was coming in fitful gusts, sending the biplane first to one side and then to the other.  They struck a “bank,” and he had to use all his wit and courage to bring the flying machine to a level keel once more.

“Better go down!” cried Tom.  “This is getting dangerous.”

“Don’t go down here!” sang out Dick.  “There are woods on both sides of the track!”

Sam had been working the horizontal rudder, to bring the biplane down, but at Dick’s words he shifted again and they went up.

“I’ll tell you when we reach an open field,” went on the oldest Rover.  “Say, this sure is some blow!” he added.

Another fitful gust struck the Dartaway and for one brief moment it looked as if the biplane would be turned over.  Had this occurred the machine would have dropped like a shot and most likely all of the boys would have been killed.

But Sam was on guard, and worked his levers like lightning.  As quickly as she had tipped, the Dartaway righted herself, and then they shot upward on a long slant.

“Phew! that was some escape!” muttered Tom.  “Dick, can’t you see any open field where we can land?”

“Must be one ahead,” was the answer.  “I fancy——­”

Dick did not finish, for at that moment came a blast of air stronger than any that had gone before.  The Dartaway spun around, left the railroad tracks, made a semi-circle, and then came back again.  As it made the final turn there was a crack like that of a pistol.

“What was that?” cried Tom.  “Was it the engine?”