The airship when completed was not unlike a huge bird with wings outstretched. The body of the bird consisted of the car and engine. The wings were planes of lath strengthened with aluminium, and capable of being inclined at any desired angle by the simple movement of a switch in the car. A large rectangular plane projecting from the rear of the car acted as a rudder, principally for lateral movement, motion upwards and downwards being provided for either by the inclination of the larger planes or by the special screws actuated by the engine. The latter drove two sets of propellers: one fore and aft, giving a horizontal movement, the other below and above the car, giving a vertical movement. Either set of propellers could be thrown out of gear when desired. Tom would have been glad to dispense with the vertical propellers if he could have done so, but he found that the whole force of his engine was necessary to raise the airship from a position of rest. He had not sufficient motive power to enable him to use such an adjustment of oblique propellers as would have ensured simultaneous horizontal and vertical movement. Mr. Greatorex at once promoted the fortunate young chemist who had discovered the virtues of the Schlagintwert powder, and swore him to secrecy. The parts of Tom’s machine were made to his order by various firms, the work being distributed so that no one firm should be in possession of the complete apparatus; and a few weeks before Herr Schwab’s visit, an aeroplane capable of sustaining the weight of several men was finished, and in it Tom made daily trips about the field. He tested it so frequently that he used considerable quantities of the powder, and it was not surprising that the curiosity of Schlagintwerts was aroused by the large orders that came from one small place for an article that cost a good deal more than its weight in gold. Tom was, however, not yet satisfied with his machine. For one thing he had found it impossible as yet to return to earth with any exactitude at a fixed spot. It was a matter of the nice adjustment of the horizontal with the vertical motion, and after repeated failures Tom comforted himself with the thought that it must be only after long practice that an engine driver could pull his locomotive up to a nicety. Obviously much more practice must be required when the task was infinitely more difficult. Further, in spite of the jacket around the turbine, the heat generated was still too great to allow of travelling any great distance in safety, and the prospective usefulness of the aeroplane was discounted accordingly. It was Mr. Greatorex who suggested a possible way out of the difficulty. “Why not have two engines instead of one?” he said. “If one breaks down—why, there’s the other.” “It means more weight,” said Tom ruefully, “and therefore less speed and less carrying capacity.”