[Illustration: Path taken by aircraft headed so as to counteract drift.] When two or more beacon stations are available, and positions can be ascertained at least once an hour, observation on the surface of the ocean for drift, although desirable, is not absolutely necessary. The drift may be calculated with accuracy enough from the craft's position as found by the lines of bearing indicated in messages from the various beacon stations. Another method of employing the Wireless Direction Finder is for aircraft to send out signals to two or more beacon stations, which reply by advising the air navigator of his bearing in relation to themselves. This is, perhaps, the most accurate method. Its disadvantage lies in the fact that whereas the heavier and more robust apparatus needed for it can easily be employed in the stationary beacon stations, few aircraft will be able to support wireless sending apparatus of sufficient weight to carry over the long distances they must cover in trans-oceanic aërial travel. The greatest advantage of air navigation by means of wireless telegraphy is that it can be employed in any weather. Fogs and clouds do not make it inoperative, nor even less accurate. Another recommendation is that its use does not entail a knowledge of advanced mathematics, as required for navigation by astronomical observation. I believe firmly that the air navigator of the future will rely upon the Wireless Direction Finder as his mainstay, while using astronomical observation and the system of "Dead Reckoning" as checks upon the wireless bearings given him, and as second and third strings to his bow, in case the wireless receiving apparatus breaks down. CHAPTER X THE FUTURE OF TRANSATLANTIC FLIGHT Although three pioneer flights were made across the Atlantic during the summer of 1919, the year passed without bringing to light any immediate prospect of an air service between Europe and America. Nor does 1920 seem likely to produce such a development on a regular basis. Before a transatlantic airway is possible, much remains to be done--organization, capitalization, government support, the charting of air currents, the establishment of directional wireless stations, research after improvements in the available material. All this requires the spending of money; and for the moment neither governments nor private interests are enamored of investments with a large element of speculation. But, sooner or later, a London-New York service of aircraft must be established. Its advantages are too tremendous to be ignored for long. Prediction is ever dangerous; and, meantime, I am confining myself to a discussion of what can be done with the means and the knowledge already at the disposal of experts, provided their brains are allied to sufficient capital.