In time, no doubt, flying-machines of quite different types will be invented. Quite possibly the machines of the Wright model will become altogether obsolete. But this can have no possible effect upon the position that the Wright brothers themselves must always hold in the history of scientific progress. The men who fly from New York to San Francisco, or from New York to London, will be carrying out the work of the Dayton pioneers; and no future accomplishment of the heavier-than-air machine can possibly rank in historical importance with that first flight in the presence of witnesses made December 17, 1903. Then and there it was successfully demonstrated that the last difficulty, so far as joining theory and practice was concerned, had been mastered. Potentially, from that moment, the conquest of the air was complete; and the names of the conquerors as all the world knows, and as throughout the future all must remember, are Wilbur and Orville Wright. APPENDIX REFERENCE LIST AND NOTES CHAPTER II THE HIGHWAY OF THE WATERS (pp. 77-79). The _Great Eastern_. The quotation is from _Ancient and Modern Ships_, by Sir George C. V. Holmes, K.C.V.O., London, 1906. CHAPTER III SUBMARINE VESSELS (pp. 95, 98). The first submarine. As stated in the text the quotation is from a letter written to Thomas Jefferson by David Bushnell, and published in the _Transactions of the American Philosophical Society_ in 1789. (pp. 104-105). A successful diving boat. The quotation is from _The Naval History of the Civil War_, by Admiral Porter. CHAPTER IV THE STEAM LOCOMOTIVE (pp. 127, 128). George Stephenson's locomotive of 1825. The quotation is from _The History of the First Locomotive in America_, by William H. Brown, New York 1874. CHAPTER VI THE DEVELOPMENT OF ELECTRIC RAILWAYS (pp. 179-181). Early experimental railways. The quotation is from the article on "Street and Electric Railways," by Thomas Commerford Martin, in the Special Report of the U. S. Census Office on Street and Electric Railways, Washington, 1905. CHAPTER IX NAVIGATING THE AIR (p. 247). Henson's studies of the flying-machine. The quotation is from _Travels in Space_, by E. Seton Valentine and F. L. Tomlinson, New York, 1902. CHAPTER X THE TRIUMPH OF THE AEROPLANE (p. 275). How the air supports a heavier-than-air mechanism. The quotation is from an article on "The Flying Machine," by Professor S. P. Langley, in _McClure's Magazine_ for June, 1897. (p. 284). Langley's aerodrome. The description is from Professor Langley's own account in _McClure's Magazine_, above cited. (pp. 289, 290). Experiments of the Wright brothers. The quotation is from an article on "The Wright Brothers' Aeroplane," by Orville and Wilbur Wright, in _The Century Magazine_ for September, 1908.