Monsieur Roger, understanding what was going on in the brain of his friend, took care not to disturb him. He waited, hoping for an answer. His hope was soon realized. As they reached the park, Paul, who, after thinking a great deal, had failed to solve the difficulty, said, all of a sudden,—

"Monsieur Roger!"

"What, my friend?"

"How did you measure the tower?"

Monsieur Roger looked at Paul, and, affecting a serious air, he said,—

"It is impossible, entirely impossible for me to answer."

"Impossible?" cried Paul, in surprise.

"Yes, impossible."

"Why, please?"