"Briefly, the terms of the contest are as follows: any type of machine or engine can be employed, and as many descents as are necessary to replenish fuel and stores. A start can be made from any place chosen by the competitor, but the machine must finish at the same spot within twenty days. Again, any route can be chosen, so that full advantage can be taken of existing air stations, but--and this is a vital point--in order to fairly circumnavigate the globe, competitors must pass within one degree of a position immediately opposite the starting-point. Do you follow me?"
"What is known in navigation as Great Circle Sailing," replied Bramsdean. "If a start is made somewhere on the 50th parallel North, the halfway time will be somewhere 50 degrees South, with a difference of 180 degrees of longitude."
"That's it," agreed Sir Reginald. "Now the difficulty arises where to find two suitable places answering to these conditions. With the exception of a small part of Cornwall the whole of Great Brita