'But so that it may be enabled to raise heavier weights and to lift men in the air, let us take double the quantity of copper, 1,232 square feet, equal to 308 lbs. of copper; with this double quantity of copper we could construct a vessel of not only double the capacity, but of four times the capacity of the first, for the reason shown by my fourth supposition. Consequently the air contained in such a vessel will be 718 lbs. 4 2/3 ounces, so that if the air be drawn out of the vessel it will be 410 lbs. 4 2/3 ounces lighter than the same volume of air, and, consequently, will be enabled to lift three men, or at least two, should they weigh more than eight pesi each. It is thus manifest that the larger the ball or vessel is made, the thicker and more solid can the sheets of copper be made, because, although the weight will increase, the capacity of the vessel will increase to a greater extent and with it the weight of the air therein, so that it will always be capable to lift a heavier weight. From this it can be easily seen how it is possible to construct a machine which, fashioned like unto a ship, will float on the air.' With four globes of these dimensions Lana proposed to make an aerial ship of the fashion shown in his quaint illustration. He is careful to point out a method by which the supporting globes for the aerial ship may be entirely emptied of air; (this is to be done by connecting to each globe a tube of copper which is 'at least a length of 47 modern Roman palm).' A small tap is to close this tube at the end nearest the globe, and then vessel and tube are to be filled with water, after which the tube is to be immersed in water and the tap opened, allowing the water to run out of the vessel, while no air enters. The tap is then closed before the lower end of the tube is removed from the water, leaving no air at all in the globe or sphere. Propulsion of this airship was to be accomplished by means of sails, and also by oars. Lana antedated the modern propeller, and realised that the air would offer enough resistance to oars or paddle to impart motion to any vessel floating in it and propelled by these means, although he did not realise the amount of pressure on the air which would be necessary to accomplish propulsion. As a matter of fact, he foresaw and provided against practically all the difficulties that would be encountered in the working, as well as the making, of the aerial ship, finally coming up against what his religious training made an insuperable objection. This, again, is best told in his own words:-- 'Other difficulties I do not foresee that could prevail against this invention, save one only, which to me seems the greatest of them all, and that is that God would surely never allow such a machine to be successful, since it would create many disturbances in the civil and political governments of mankind.'