captive dirigible balloon driven by a pair of oscillating wings. As late as 1904 Mr. Thomas Moy, in a paper read to the Aeronautical Society of Great Britain, maintained that the greatest hindrances to the solution of the problem of mechanical flight have always been the balloon and the airscrew. Mr. William Cochrane, in a paper read a few months earlier, laid it down that the airscrew must give place to a more efficient form of propulsion. Utterances like these help to explain the fervour with which Santos Dumont, in the book called _My Airships_ (1904), defends the rotary principle, which is the life of machines. Like the Wrights, he believed in practice, and was a skilled and experienced balloonist before he attempted to navigate an airship. His first airship was almost absurdly small; it had little more than six thousand feet of cubic capacity, was cigar-shaped, and was driven by a three and a half horse-power petrol motor. The others followed in rapid succession. M. Deutsch de la Meurthe had offered a prize of a hundred thousand francs for the first airship that should rise from the Aero Club ground at St. Cloud and voyage round the Eiffel Tower, returning within half an hour to its starting-point. On the 19th of October 1901 the prize was won by Santos Dumont in the sixth of his airships. The ship had over twenty-two thousand feet of cubic capacity; its length was more than five times its diameter; and it was driven by a twelve horse-power petrol motor. It travelled six and three-quarter miles within the half-hour, part of the journey being accomplished against a wind of about twelve miles an hour. This achievement quickened interest in airships and gained a European fame for Santos Dumont. His later airships were modelled on the egg rather than the cigar; the smallest of these was so perfectly under control that he was able, he says, to navigate it by night through the streets of Paris.