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"I'll go take a look." Rong Xi spoke and headed over at once.

Qin Ke went with him, and Cheng Hao was unwilling to fall behind.

When the three arrived, all the craftsmen stopped working and bowed.

Rong Xi looked at the timber on the ground. It was indeed heavy. The craftsmen stood atop a raised platform and used pulleys to hoist the load; with such weight, it was only natural for the rope to snap.

Yet as he studied the pulley, he saw that it merely changed the direction of force and could not save effort.

The pulley was what later generations called a sheave.

Rong Xi suddenly asked, "Uncle Cheng, do the craftsmen have pulley blocks?"

"Pulley blocks?" Cheng Hao did not understand. "What are those?"

Rong Xi looked around, spotted a dead branch nearby, picked it up, and scratched a diagram into the ground.

"Uncle Cheng, common folk often use windlasses to draw water from wells, while craftsmen use pulleys to lift heavy objects. The principles behind them are no different, are they?"

Cheng Hao nodded seriously. "They are indeed the same."

All the craftsmen gathered around to listen to Rong Xi.

Rong Xi drew on the ground and continued, "A pulley only changes the direction of force; it cannot reduce the effort needed. But with pulley blocks, it may be possible."

A complete pulley-block system took shape on the ground. Though the crowd did not understand it at once, there was no shortage of clever minds among them.

Cheng Hao was quite gifted. He frowned as he studied the drawing on the ground, pondering for a long while. Then a flash of insight struck him, as though his Ren and Du meridians had suddenly opened. Light blazed in his eyes, and his beard trembled.

"Excellent! Truly