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. Later, because of some knowledge obtained from a Martian newspaper by Jack, they all made a trip to the moon in search of a field of diamonds, and their adventures as related in "Lost on the Moon" were of the most thrilling kind. The projectile brought them safely home again and they had now, for some months, been quietly pursuing their usual avocations.