He ends by saying that no city would be proof against surprise, while the aerial ship could set fire to vessels at sea, and destroy houses, fortresses, and cities by fire balls and bombs. In fact, at the end of his treatise on the subject, he furnishes a pretty complete resume of the activities of German Zeppelins. As already noted, Lana himself, owing to his vows of poverty, was unable to do more than put his suggestions on paper, which he did with a thoroughness that has procured him a place among the really great pioneers of flying. It was nearly 200 years before any attempt was made to realise his project; then, in 1843, M. Marey Monge set out to make the globes and the ship as Lana detailed them. Monge's experiments cost him the sum of 25,000 francs 75 centimes, which he expended purely from love of scientific investigation. He chose to make his globes of brass, about.004 in thickness, and weighing 1.465 lbs. to the square yard. Having made his sphere of this metal, he lined it with two thicknesses of tissue paper, varnished it with oil, and set to work to empty it of air. This, however, he never achieved, for such metal is incapable of sustaining the pressure of the outside air, as Lana, had he had the means to carry out experiments, would have ascertained. M. Monge's sphere could never be emptied of air sufficiently to rise from the earth; it ended in the melting-pot, ignominiously enough, and all that Monge got from his experiment was the value of the scrap metal and the satisfaction of knowing that Lana's theory could never be translated into practice. Robert Hooke is less conspicuous than either Borelli or Lana; his work, which came into the middle of the seventeenth century, consisted of various experiments with regard to flight, from which emerged 'a Module, which by the help of Springs and Wings, raised and sustained itself in the air.' This must be reckoned as the first model flying machine which actually flew, except for da Vinci's helicopters; Hooke's model appears to have been of the flapping-wing type--he attempted to copy the motion of birds, but found from study and experiment that human muscles were not sufficient to the task of lifting the human body. For that reason, he says, 'I applied my mind to contrive a way to make artificial muscles,' but in this he was, as he expresses it, 'frustrated of my expectations.' Hooke's claim to fame rests mainly on his successful model; the rest of his work is of too scrappy a nature to rank as a serious contribution to the study of flight.