He flew on, his head phones still plugged in. Sounding endlessly he could hear the steady stroke of the Air Mail radio beacon sending a string of dashes—“dah, dah, dah, dah, dah, dah,” which tells the pilot when he is exactly on the line. Jimmy had small need of any such help this morning, for the air was so clear that he could see for miles in every direction. But he thought of the invaluable help this radio beacon must be to the mail pilots in the fog. The device had been perfected since Jimmy was a mail pilot. He had never carried mail under its guidance. But he was as well equipped to profit by it as any mail pilot was. More than once he had been helped in bad weather by this very same signal, as he flew along the mail route. In a sense he was helped now. A little breeze had been coming up, that blew across the line of flight. Jimmy was being blown to one side, without realizing it. Of course he would presently have noticed that fact anyway, and brought his ship back to the line, but the signal in his ears gave him prompt warning. No longer did he hear the steady beat: “dah, dah, dah, dah, dah, dah.” Instead, the head phones were saying: “dot dah, dot dah, dot dah, dot dah, dot dah.” The radio signal had changed to dot dash, dot dash. That told Jimmy that he was to the left of the line. He knew that if he had chanced to be on the right side of the line instead, the signals would have changed to dash dot, dash dot, and his head phones would have said: “dah dot, dah dot, dah dot, dah dot.” He nosed his ship a little into the wind, and presently he was right over the line once more, and the head phones again were singing: “dah, dah, dah, dah, dah, dah.” “Gee,” thought Jimmy, “if only they had had the radio beacon from the start, how very many tragedies the Air Mail would have been saved. It’s fine for the men who are carrying the mail now. They always know when they are on the line, even if it is so foggy they can’t see a thing. If it just weren’t for these old Pennsylvania mountains, flying the eastern leg of the Air Mail would be pie. But I guess this leg will always be a graveyard. Hello, here’s Ringtown. I’ve got to be thinking about getting down.” CHAPTER III Jimmy Meets an Old Friend—Johnnie Lee, of the Wireless Patrol