“Then you travelled east by north about a fifteenth of a mile and we shall put down half an inch on the chart. Then you turned northeast. How long did you go on?”

“Exactly a minute. The next entry is ‘Nine. West northwest.’ ”

“Then you travelled about the seventh of a mile in a northeasterly direction and we draw a line an inch long at an angle of forty-five degrees to the right of the north and south line. From the end of that we carry a line at an angle of fifty-six and a quarter degrees to the left of the north and south line, and so on. The method is perfectly simple, you see.”

“Perfectly; I quite understand it now.”