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, threatening the whole party with death and the flying machine itself with destruction, at every jump.

CHAPTER II

MARK HANGS ON

Professor Henderson and his adopted sons—Jack Darrow and Mark Sampson—had been in many perilous situations together. Neither one nor the other was likely to display panic at the present juncture, although the flying Snowbird was playing a gigantic game of "leap-frog" through the air.

The professor had himself constructed many wonderful machines for transportation through the air, under the ground, and both on and beneath the sea; and in them he and his young comrades had voyaged afar.

Narrated in the first volume of this series, entitled, "Through the Air to the North Pole," was the bringing together of the two boys and the professor,—how the scientist and Washington White rescued Jack and Mark after a train wreck, took them to the professor's workshop, and made the lads his special care. In that workshop was built the Electric Monarch, in which flying ship the party actually passed over that point far beyond the Arctic Circle where the needle of the compass indicates the North Pole.

Later, in the submarine boat, the Porpoise, the professor, with his young assistants and others, voyaged under the sea to the South Pole, the details of which voyage are related in the second volume of the series, entitled "Under the Ocean to the South Pole."

In the third volume, "Five Thousand Miles Underground," is related the building of that strange craft, the Flying Mermaid, and how the voyagers journeyed to the center of the earth. The perils connected with this experience satisfied all of them, as far as adventure went, for some time. Jack and Mark prepared for, and entered, the Universal Electrical and Chemical College.

Before the first year of their college course was completed, however, Professor Henderson, in partnership with a brother scientist, Professor Santell Roumann, projected and carried through a marvelous campaign with the aid of Jack and Mark, which is narrated in our fourth volume, entitled, "Through Space to Mars." In this book is told how the projectile, Annihilator, was built and, the projectile being driven by the Etherium motor, the party was transported to the planet Mars.