cheap material; for the probabilities were, the substance would be cheaply producible. Each aerial vessel should carry three or four times the number of separate fans and machinery necessary to obtain buoyancy. The same substances probably could be used to procure buoyancy in the improbable event of all the machines breaking down. Supposing, as he suspected would be the case, that the resultant gas of the decomposition was lighter than air, a hollow case of a strong elastic fabric could be fastened to the whole of the outside exposed surface of the machine; and this could be rapidly inflated by the use of the same material. The movement of a button should be sufficient to produce decomposition, and as a consequence to charge the whole of this casing with gas lighter than the air. As the heat attending the decomposition subsided the elastic fabric would sufficiently collapse. The danger then would not be so much of descending too rapidly through the atmosphere as of remaining in it; a difficulty, however, which a system of valves would easily overcome. The Institution offered twenty-five thousand pounds for a discovery on the lines indicated; and the Government offered seventy-five thousand pounds more on the condition that they should have the right to purchase the invention and preserve it as a secret, they supplying the material for civil purposes, but retaining absolute control over it for military purposes. This proviso was inserted because of the opinion of the writer that the effects he looked for might not so much depend on the chemical composition of the substances as on their molecular conditions, and that these might defy the efforts of analysts. If he was wrong, and the nature of the compound could be ascertained by analysis, the Government need not buy the invention; they could leave the discoverer to enjoy its advantages by patenting it, and share with other nations the uses that could be made of it for purposes of warfare.