Tom took his model, and patiently expounded the mechanical principles on which he had worked. The upshot of this and other conversations was that Mr. Greatorex became first interested, then enthusiastic, and finally determined. He had a workshop erected on a large piece of waste ground nearly a mile and a half square on his estate, and gave Tom carte blanche to get what assistance and spend what money he pleased. Resolving to keep the matter a close secret until the experiments were concluded, he fenced in the enclosure, and gave strict orders that no one was to be admitted to it without Tom’s consent. Tom himself devised a simple means of defending the workshop from prying visitors. Whenever he left it, he set going a strong electric current through the door handle, which was a more effective protection than locks and bolts. Tom found, as soon as he came to enlarge his model into a practical working size, that none of the motors then on the market was sufficiently powerful in proportion to its weight to give him the necessary lifting force. The electric motor was out of the question, and an adaptation of the latest petrol engine as applied to motor-cars and launches seemed to offer the most likely solution. Even here, however, the march of invention had not gone far enough. The latest petrol motor, it is true, enabled Tom to keep the machine at a constant altitude when once it was in flight; but it failed to raise it from a position of rest. Some other method must be found, and he set his wits to work to discover it. The first condition of success was, he felt, the discovery of an explosive mixture far more powerful than that offered by petrol, and yet capable of being harnessed and controlled. He had the run of Mr. Greatorex’s chemical laboratories, and the benefit of the practical advice and assistance of the heads of the experimental staff. Scores of preparations were tried, and, for one reason or another, rejected. Where sufficient power was obtained, it was almost invariably found that the mixture was not stable or uniform in its effects. Several explosive mixtures were discovered quite powerful enough for the purpose; but, as Mr. Greatorex’s chief chemist pointed out, all of them were likely to blow the airship to smithereens in the event of any accident to the machinery.