All inventors profit, or should profit, by the experience of others, whether such experience be gained by success or failure. It was found that Santos-Dumont's air-ship lost a considerable amount of gas when driven through the air, and on several occasions the whole craft was in great danger of collapse. To keep the envelope inflated as tightly as possible Mr. Spencer, by a clever contrivance, made it possible to force air into the balloon to replace the escaped gas. The first Spencer air-ship was built for experimental purposes. It was able to lift only one person of light weight, and was thus a great contrast to the modern dirigible which carries a crew of thirty or forty people. Mr. Spencer made several exhibition flights in his little craft at the Crystal Palace, and so successful were they that he determined to construct a much larger craft. The second Spencer air-ship, first launched in 1903, was nearly 100 feet long. There was one very important distinction between this and other air-ships built at that time: the propeller was placed in front of the craft, instead of at the rear, as is the case in most air-ships. Thus the craft was pulled through the air much after the manner of an aeroplane. In the autumn of 1903 great enthusiasm was aroused in London by the announcement that Mr. Spencer proposed to fly from the Crystal Palace round the dome of St. Paul's Cathedral and back to his starting-place. This was a much longer journey than that made by Santos-Dumont when he won the Deutsch prize. Tens of thousands of London's citizens turned out to witness the novel sight of a giant air-ship hovering over the heart of their city, and it was at once seen what enormous possibilities there were in the employment of such craft in time of war. The writer remembers well moving among the dense crowds and hearing everywhere such remarks as these: "What would happen if a few bombs were thrown over the side of the air-ship?" "Will there be air-fleets in future, manned by the soldiers or sailors?" Indeed the uppermost thought in people's minds was not so much the possibility of Mr. Spencer being able to complete his journey successfully--nearly everyone recognized that air-ship construction had now advanced so far that it was only a matter of time for an ideal craft to be built--but that the coming of the air-ship was an affair of grave international importance.