At the next IDC meeting, the chair produced a custom-made umbrella that looked just like the one in the fairy tales. The black umbrella had eight ribs, and at the end of each was a small stone sphere. In this era, umbrellas were no longer in common use. To avoid the rain, modern people used something called a rainshield, a device about the size of a flashlight that protected the user by blowing air up to form an invisible canopy. People certainly knew about umbrellas and saw them in movies, but few had experience with the real thing. Curious, they played with the chair’s umbrella, and noticed that, just like in the stories, the canopy could be kept open by spinning. Spinning faster or slower resulted in corresponding alarm sounds.
“This is really tiring,” someone complained as he spun the umbrella.
Everyone gained new respect for the princess’s wet nurse, who’d managed to spin the umbrella nonstop for a whole day.
AA took over the umbrella. Her hands weren’t as strong, and the canopy began to fall. They all heard the warning birdsong.
Cheng Xin had kept her eyes on the umbrella since the chair had opened it. Now she cried out to AA, “Don’t stop!”
AA spun faster, and the birdsong stopped.
“Faster,” said Cheng Xin.
AA put all her strength into spinning, and the wind chime began to play. Then Cheng Xin asked her to slow down, until the birdsong appeared. This went back and forth a few times.
“This is not an umbrella at all!” said Cheng Xin. “But I know what it is now.”
Bi Yunfeng, who stood to the side, nodded. “Me too.” Then he turned to Cao Bin. “Probably only the three of us can recognize this object.”
“Yes,” said an excited Cao. “But even in our time, this was rarely seen.”
Some of the attendees looked at these three individuals from the past; others looked at the umbrella. All were puzzled, but also expectant.
“It’s a centrifugal governor,” said Cheng Xin. “For steam engines.”
“What’s that? Some kind of control circuit?”
Bi Yunfeng shook his head. “The world wasn’t electrified back when this was invented.”
Cao Bin explained. “This was a device from the eighteenth century for regulating the speed of a steam engine. It’s made of two or four lever arms equipped with spherical masses at the ends and a central spindle with a sleeve—it looks just like this umbrella, except with fewer ribs. The steam engine’s operation rotates the spindle. When it spins too fast, the metal balls lift the lever arms due to centrifugal force, which pulls up on the sleeve and reduces the aperture of the throttle valve connected to the sleeve, thereby reducing the fluid entering the cylinder and the engine’s speed. Conversely, when it spins too slowly, the lever arms fall due to the weight of the metal balls—like an umbrella closing—and the sleeve is pushed down, increasing the aperture of the throttle valve and the speed of the engine…. This was one of the earliest industrial automatic control systems.”
Thus was the first level of the dual-layer metaphor in the umbrella decoded. But unlike the soap-propelled boat, the centrifugal governor didn’t seem to clearly point to anything. This second-layer metaphor could be interpreted in multiple ways, with two possibilities deemed most likely: negative-feedback automatic control and constant speed.
The interpreters began to look for the corresponding bearing coordinate for this dual-layer metaphor. Soon, they fixed on Prince Deep Water. The prince’s height didn’t change in the observers’ eyes regardless of distance. This could also be interpreted in multiple ways, with two possibilities being most obvious: a method of information transmission where the signal strength did not decay due to distance, or a physical quantity that remained constant regardless of the frame of reference used.
Taken together with the metaphorical meanings of the umbrella, the true meaning instantly emerged: a constant speed that did not change with the frame of reference.
Clearly, it referred to the speed of light.
Unexpectedly, the interpreters found yet another bearing coordinate for the metaphor of the umbrella.
