Apart from these two experimenters, there is little to record in the matter either of experiment or study until the seventeenth century. Francis Bacon, it is true, wrote about flying in his _Sylva Sylvarum_, and mentioned the subject in the _New Atlantis_, but, except for the insight that he showed even in superficial mention of any specific subject, he does not appear to have made attempt at serious investigation. ‘Spreading of Feathers, thin and close and in great breadth will likewise bear up a great Weight,’ says Francis, ‘being even laid without Tilting upon the sides.’ But a lesser genius could have told as much, even in that age, and though the great Sir Francis is sometimes adduced as one of the early students of the problems of flight, his writings will not sustain the reputation. The seventeenth century, however, gives us three names, those of Borelli, Lana, and Robert Hooke, all of which take definite place in the history of flight. Borelli ranks as one of the great figures in the study of aeronautical problems, in spite of erroneous deductions through which he arrived at a purely negative conclusion with regard to the possibility of human flight. Borelli was a versatile genius. Born in 1608, he was practically contemporary with Francesco Lana, and there is evidence that he either knew or was in correspondence with many prominent members of the Royal Society of Great Britain, more especially with John Collins, Dr Wallis, and Henry Oldenburgh, the then Secretary of the Society. He was author of a long list of scientific essays, two of which only are responsible for his fame, viz., _Theorice Medicæarum Planetarum_, published in Florence, and the better known posthumous _De Motu Animalium_. The first of these two is an astronomical study in which Borelli gives evidence of an instinctive knowledge of gravitation, though no definite expression is given of this. The second work, _De Motu Animalium_, deals with the mechanical action of the limbs of birds and animals and with a theory of the action of the internal organs. A section of the first part of this work, called _De Volatu_, is a study of bird flight; it is quite independent of Da Vinci’s earlier work, which had been forgotten and remained unnoticed until near on the beginning of practical flight. Marey, in his work, _La Machine Animale_, credits Borelli with the first correct idea of the mechanism of flight. He says: ‘Therefore we must be allowed to render to the genius of Borelli the justice which is due to him, and only claim for ourselves the merit of having furnished the experimental demonstration of a truth already suspected.’ In fact, all subsequent studies on this subject concur in making Borelli the first investigator who illustrated the purely mechanical theory of the action of a bird’s wings.