He was very curious by this time, for he had been thinking about them and it had struck him that they were too much in earnest to simply be enjoying lark. But Harry and Dick, while they met his questions politely, refused to enlighten him.
"I'm sorry, sir," said Harry, when the old gentleman pressed him too hard. "But I really think we mustn't tell you why we're here. But if you would like to hear of it later, we'll be glad to come to see you and explain everything."
"Bless my soul!" said the old man. "When I was a boy we didn't think so much of ourselves, I can tell you! But then we didn't have any Boy Scouts, either!"
It was hard to tell from his manner whether that was intended for a compliment or not. But they waited no longer. In a trice they were on their motorcycles and off again. And when they drew near to the hilltop whence the signals had come, Harry stopped. For a moment he looked puzzled, then he smiled.
"I think I've got it!" he said. "They're clever enough to try to fool anyone who got on to their signalling. They would know what everyone would think—that they would be sending their messages to the East coast, because that is nearest to Germany. That's why they put their first station here. I'll bet they send the flashes zig-zagging all around, but that we'll find they all get east gradually. Now we'll circle around this one until we find out in what direction it is flashing, then we'll know what line we must follow. After that all we've got to do is to follow the line to some high hill or building, and we'll pick up the next station."
Their eyes were more accustomed to the work now, and they wasted very little time. This time, just as Harry had guessed, the flashes were being sent due east, and judging from the first case that the next station would be less than ten miles away, he decided to ride straight on for about that distance. He had a road map, and found that they could follow a straight line, except for one break. They did not go near the hilltop at all.
"I'd like to know what they're doing there," said Dick.
"So would I, but it's open country, and they're probably keeping a close lookout. They're really safer doing that in the open than on the roof of a house, out here in the country."
"Because they can hide the heliograph? It's portable, isn't it?"
"Yes. They could stow it away in a minute, if they were alarmed. I fancy we'll find them using hilltops now as much as they can."