The finger of the speed indicator whirled and marked forty miles an
hour ere the flying machine left the steel plank, and shot into the
air with the fearful force of the compressed air behind it.

Both Mark and Jack were well used to guiding aeroplanes and other air
machines. But this start from the ground was much different from the
easy, swooping flight of an airship as usually begun. Like an arrow
the _Snowbird_ was shot upward on a long slant. It was a moment
ere Mark got the controls to working. The propellers were, of course,
started with the first stroke of the motor.

But Mark Sampson was nervous; there was no denying that. At the instant
when the nose of the airship should have been raised, so as to clear
the tops of the forest trees and every building on the Henderson place,
Mark instead guided the rapidly flying _Snowbird_ far to the left.

It skimmed the corner of the stable by a fraction of a foot, and Jack
yelled:

"Look out!"

His cry made Mark even more nervous. The tall water-tank and windmill
were right in line. Before the young aviator could swerve the flying
machine to escape the vane upon the roof of the tower, and the long
arms of the mill, they were right upon these things!

The fast-shooting _Snowbird_ was jarred through all her members; but she
tore loose. And then, in erratic leaps and bounds, she kept on across
the fields and woods towards Easton, never rising very high, but
occasionally sinking so that she trailed across the treetops,