There remained only the hope that some means might be found of buoying man up in the air, thereby leaving him free to apply his muscular and mechanical powers to the business of driving himself forward. Another celebrated treatise of the seventeenth century pointed the way to such a means. Francesco Lana, a member of the Society of Jesus in Rome, spent the greater part of his life in scientific research. He planned a large encyclopaedia, embodying all existing science, in so far as it was based on experiment and proof. Of this work only two volumes appeared during his lifetime; he died at Brescia in the year 1687. But long before he died, he had produced, in 1670, a preliminary sketch of his great work; and it is this earlier and shorter treatise which contains the two famous chapters on the Aerial Ship. The aerial ship is to be buoyed up in the air by being suspended from four globes, made of thin copper sheeting, each of them about twenty-five feet in diameter. From these globes the air is to be exhausted, so that each of them, being lighter than air, will support the weight of two or three men. The ship being thus floated can be propelled by oars and sails. Any modern reader, without asking for further specifications, can pronounce this design absurd. Lana was prevented by his vow of poverty from spending any money on experiment, so that he had to meet only argumentative objections, not those much more formidable obstacles, the ordeal of the inventor, which present themselves when a machine is theoretically perfect and will not work. The difficulties which he foresaw are real enough. The process of exhausting the air from the globes might, he thought, prove troublesome. The pressure of the atmosphere on the outer surface, it might be held, would crush or break the globes, to which he replied that that pressure would be equal on all sides, and would therefore rather strengthen the globes than break them. The ship, some might object, could not be propelled by oars; Lana thinks it could, but suggests, to comfort the objectors, that oars will rarely be necessary, for there will always be a wind. The weight of the machine and of the persons in it will fortunately prevent it from rising to heights where breathing becomes impossible. 'I do not foresee', says Lana, 'any other difficulties that could prevail against this invention, save one only, which to me seems the greatest of them all, and that is that God would never surely allow such a machine to be successful, since it would create many disturbances in the civil and political governments of mankind. Where is the man who can fail to see that no city would be proof against surprise, when the ship could at any time be steered over its squares, or even over the courtyards of dwelling-houses, and brought to earth for the landing of its crew?... Iron weights could be hurled to wreck ships at sea, or they could be set on fire by fireballs and bombs; nor ships alone, but houses, fortresses,