Several of the children stifled sobs.

He abandoned his effort to write on the blackboard. He waved his hand, and a child came over to remove it from his chest. In a small voice, almost a whisper, he began to speak.

“Like our lessons yesterday and the day before, today’s lesson is meant for middle schoolers. It is not on your syllabus. Most of you will never have a chance to attend middle school, so I thought I would give you a taste of what it’s like to study a subject in greater depth. Yesterday, we read Lu Xun’s Diary of a Madman. You probably didn’t understand much of it, but I want you to read it a few more times, or, better yet, learn to recite it from memory. You’ll understand it when you’re older. Lu Xun was a remarkable man. Every Chinese person should read his books. I know all of you will in the future.”

He stopped speaking to rest for a moment and catch his breath. He looked at the flickering candle flame. Another passage of Lu Xun came to him. It wasn’t from Diary of a Madman, and it hadn’t been in his textbook. He had encountered it many years before, in his own incomplete, thumbed-through set of Lu Xun’s collected works. Since the first time he read it, he hadn’t forgotten a single word.

Imagine a windowless, iron room. Many people lie asleep inside. They will soon suffocate and die in their sleep. You shout, and a few hopeless sleepers awaken to a wretched fate that you are powerless to prevent. Have you done them a favor?

Unless you wake them up, what hope do they have of escape?

With the last of his strength, he continued his lecture.

“Today’s class is middle school physics. You may not have heard of physics before. It is the study of the principles of the physical world. It’s an extremely rich, deep field of knowledge.

“We will learn about Newton’s three laws. Newton was an important English scientist who lived a long time ago. He came up with three remarkable rules. These rules apply to everything in heaven and on Earth, from the sun and moon in the sky down to the water and air of our own planet. Nothing can escape Newton’s three truths. With them, we can calculate to the second when solar eclipses—when the ‘sun dog eats the sun,’ as our village elders say—will happen. Humans can fly to the moon using Newton’s three laws.

“The first law is as follows: A body at rest or moving in a straight line at a constant speed will maintain its velocity unless an outside force acts upon it.”

The children watched him silently in the candlelight. No one stirred.

“This means that if you took the grindstone from the mill and gave it a good push, it should keep rolling, all the way to the horizon. What are you laughing at, Baozhu? You’re right, that wouldn’t actually happen. That’s because a force called friction will bring the stone to a halt. There is nowhere in the world without friction.”