"Because in answering I will break the promise that I have made you,—the promise to say nothing about chemistry or physical science."
"Ah!" said Paul, becoming silent again.
Monsieur Roger glanced at his companion from the corner of his eye, knowing that his curiosity would soon awake again. At the end of the narrow, shady pathway they soon saw the red bricks of the château shining in the sun; but Paul had not yet renewed his question, and Monsieur Roger began to be a little uneasy,—for, if Paul held his tongue, it would show that his curiosity had vanished, and another occasion to revive it would be difficult to find.
Luckily, Paul decided to speak at the very moment when they reached the château.
"Then," said he, expressing the idea which was uppermost,—"Then it is physical science?"
Monsieur Roger asked, in an indifferent tone,—
"What is physical science?"
"Your method of measuring the tower."
"Yes, it is physical science, as you say. Consequently, you see very well that I cannot answer you."
"Ah, Monsieur Roger," said Paul, embarrassed, "you are laughing at me."