the best fabric for the envelope of an airship--these and scores of other problems were systematically and patiently attacked. There were no theatrically quick results, but the work done laid a firm and broad base for all subsequent success. Hasty popular criticism is apt to measure the value of scientific advice by the tale of things done, and to overlook the credit that belongs to it for things prevented. The science of aeronautics in the year 1909 was in a very difficult and uncertain stage of its early development; any mistakes in laying the foundations of a national air force would not only have involved the nation in much useless expense, but would have imperilled the whole structure. Delay and caution are seldom popular, but they are often wise. Those who are stung by the accusation of sloth are likely to do something foolish in a hurry. Nothing is more remarkable in the history of our aeronautical development than its comparative freedom from costly mistakes. This freedom was attained by a happy conjunction of theory and practice, of the laboratory and the factory. The speculative conclusions of the merely theoretical man had to undergo the test of action in the rain and the wind. The notions and fancies of the merely practical man were subjected to the criticism of those who could tell him why he was wrong. The rapid growth in power and efficiency of the British air force owed much to the labours of those who befriended it before it was born, and who, when it was confronted with the organized science of all the German universities, endowed it with the means of rising to a position of vantage.