d flapping of the wings. This view
received authoritative support from a famous treatise written in the
seventeenth century by Giovanni Alfonso Borelli, an Italian professor of
mathematical and natural philosophy. Borelli, who held professorships at
the Universities of Florence and Pisa, and corresponded with many
members of the Royal Society, was an older man than Wilkins, but his
book on the movements of animals (_De Motu Animalium_), which included a
section on the flight of birds (_De Volatu_), was not published till
1680, when both he and Wilkins were dead. It was long held in high
esteem for its anatomical exposition of the action of flying, and some
of its main contentions cast a damp upon the hopes of man. The bones of
a bird, says Borelli, are thin tubes of exceeding hardness, much
lighter, and at the same time stronger, than the bones of a man. The
pectoral muscles, which move the wings, are massive and strong--more
than four times stronger, in proportion to the weight they have to move,
than the legs of a man. And he states his conclusion roundly--it is
impossible that man should ever achieve artificial flight by his own
strength. This view, dogmatically stated by one who was a good
mathematician and a good anatomist, became the orthodox view, and had an
enduring influence. All imitation of the birds by man, and further, all
schemes of navigating the air in a machine dynamically supported,
seemed, by Borelli's argument, to have been thrust back into the limbo
of vanities.

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