The Experiment

One morning a few days later, Joseph once again put on a formal suit. He took Napoleon, dressed in his uniform, and climbed into a light two-wheeled carriage to attend that evening's experiment to measure the speed of light at Burton Castle, outside Paris.

Burton Castle belonged to the Orleans Family. It stood atop a small hill and was said to have been built in the twelfth century as a military fortress. By now, it had long since lost its military value. What was more, its defenses had been strengthened so much during its construction that it was almost entirely unsuitable for living in. As a result, the castle was now practically half-abandoned. It was, however, an excellent place for an experiment: it lay far from the city, with few residents nearby and almost no light pollution. From the castle's lofty tower, they could clearly see the fire reflected off a mirror some four or five leagues away (one league was about four kilometers). That was crucial for the evening's experiment.

The place was somewhat remote and a little too far from Paris for any public carriages to go there, so Joseph rented a light two-wheeled carriage for the trip.

The carriage traveled all morning, reaching the area near Burton Castle around three in the afternoon. At the foot of the hill where the castle stood was an estate belonging to the Orleans Family, and everyone who had come to take part in the experiment was gathered there. The carriage stopped at the estate's entrance, where a servant came over to inquire who they were. Joseph gave his name, and soon the estate's wrought-iron gates swung open. The carriage rolled along a stone-paved path and stopped in front of a large house with a distinct Baroque style. A servant opened the door, and Joseph and Napoleon climbed out. A powdered-wigged attendant then led them inside.

The attendant led them through the hall and out to a small garden at the back, where a little glass greenhouse stood. It was nothing special by later standards, but in this era, it was beyond the means of an ordinary household. Several people were sitting inside, drinking tea and admiring the roses in bloom. Joseph walked over and saw Condorcet, Lavoisier, Laplace, and Monge, but not their host, Duke Charles.

"Ah, Joseph, come over, come over..." As soon as he saw Joseph, Lavoisier beckoned him over. Joseph went up to them, greeted each in turn, then gave special thanks to Monge and Laplace for recommending him. Of course, to Napoleon, that thanks sounded like Joseph was thanking them for recommending his paper.

Joseph then introduced his brother. "This is my brother, Napoleon. He's studying at the Paris Military Academy. He's interested in science too, so I brought him along to broaden his horizons. By the way, why isn't His Grace here?"

"His Grace was here earlier, but a short while ago, His Majesty summoned him... We don't know what it was about," Lavoisier said. "But His Grace left his steward, Mr. Will, here to assist us. Everything is ready now, really. We're just waiting for nightfall."

Over the past few days, with the help of the Orleans Family, the people from the Academy of Sciences had precisely measured the straight-line distance from the watchtower at Burton Castle to the tops of two nearby, unnamed hills. To ensure a clear line of sight, they had cut down all the trees on those hilltops—after all, the hills also belonged to the Orleans Family.

Everything was ready; all that remained was for darkness to fall. With nothing else to do, they gathered to discuss various scientific questions. Monge and Laplace sat together, discussing the potential-function formulation of the gravitational force exerted by a celestial body on any point mass outside it. Napoleon joined them to listen, but that was all he did. Unlike Joseph, he couldn't even chime in with the occasional comment.

Just then, someone from the Orleans Family invited them to dinner. Since the experiment was about to begin, the meal was essentially a working dinner, and by the standards of the Orleans Family, it was hardly lavish. Even so, many of the dishes were things Joseph and Napoleon had never tasted before, such as slices of truffle between bread spread with foie gras, along with other things Joseph couldn't even identify as he ate them.

After the meal, they climbed back into the carriage and headed to the nearby castle. It wound its way up the twisting road and soon reached the foot of the castle.

Everyone got out. The sun in the west was already close to the horizon, growing bigger and redder by the moment.

The servants lit their lanterns and led the people from the Academy of Sciences into the old castle.

Castles were usually built with very thick stone walls and very small windows, often set deep inside, to ensure their defenses. As a result, they were poorly ventilated and lit. At dusk, of course, one needed lamps inside, but even at midday, castles were dark enough to require lighting. Little wonder that nobles rarely chose to live in them except in times of war. Now that advances in artillery had stripped these old fortresses of their military purpose, nobles were even less inclined to live in them. They were unwilling to pay even for their upkeep, so the castles generally fell into ruin. With their gloomy interiors that needed lighting even in daylight, and their crumbling, deserted halls, one after another became the setting for ghost stories. The castle they had entered now was no exception; it, too, was said to be haunted by a "castle ghost."

Joseph and Napoleon followed a servant carrying a lantern up the winding stone staircase. The servant lit the steps with his lantern and reminded them, "Sir, the castle is very damp, and moss grows on these stone steps. They're slippery, so be careful as you climb."

"Thank you. We'll be careful," Joseph replied, lowering his head to watch the steps beneath his feet.

Soon they reached the castle's highest watchtower. It was a small platform, a little over twenty meters long. At one end sat a pile of firewood, the logs soaked in whale oil. Once lit, this brazier would burn more brightly than an ordinary fire. In the dark, its flame could be clearly seen even from nine leagues away, or farther. At the other end of the platform stood a rotating octagonal mirror.

A telescope stood on the platform as well. Through it, they could see a set of mirrors already installed on the hilltop across the way.

"Have all the mirrors been adjusted?" Joseph asked.

"They have. They can reflect the light precisely onto the other face of the octagonal mirror," Monge answered in a low voice.

The sun sank lower and lower, then finally disappeared beneath the horizon, leaving only a faint lavender glow in the western sky. One star after another appeared in the darkening heavens, and before long the sky was strewn with jewel-bright stars.

When it had grown dark enough, Lavoisier said, "All right, we should be able to begin."

A servant used his torch to set the large fire alight. A firework then rose from the hilltop across the way, signaling that the people there could clearly see the fire on the castle.

After receiving the signal, everyone focused on the other face of the octagonal mirror. According to the experimental setup, light from the fire would strike one face of the rotating mirror, travel to the reflector on the other hill, and then bounce back. If, during that time, the octagonal mirror turned by exactly one face, they would be able to see the returning beam on its other face.

There was no reflection at all in that direction. The octagonal mirror spun faster and faster, but still they saw no firelight.

"Faster, faster," Joseph said, staring at the spinning mirror.

The octagonal mirror continued to accelerate. At last, the flickering firelight began to flash across the face everyone was watching.

"Hold it, hold the speed steady. Good, good! Quick, record the rotation speed!" Monge shouted.

An assistant hurriedly recorded the speed.

As soon as the figures were in, Joseph, Laplace, and Monge crowded together and began calculating by the light of the fire. Laplace got the answer first, then Monge worked it out too. Joseph, meanwhile, had only finished about two-thirds of his calculation by the time they were done.

"Ha ha, Joseph, your calculation skills aren't very good. You're so slow!" Monge burst out laughing.

Napoleon wore a grin of pure schadenfreude. From the look in his eyes, Joseph knew the fellow was thinking, My foolish brother, so you can be looked down on too.

Back in my previous life, I could've handled calculations this complicated with a single press of the Enter key. Who does this stuff by hand anymore? I'm already pretty impressive at this speed. Someone else might not even be halfway done by now. Joseph thought this as he answered with a wry smile, "I'm not very good at calculations. I can never do them quickly, and if I speed up even a little, I make mistakes. I can't help it."

The others all laughed.

Amid the laughter, Joseph finished his calculation too. The three of them compared their results, which were more or less the same. Joseph silently converted the figure into kilometers. The result was remarkably close to the speed of light measured by later generations.

"It's really that fast?" Laplace murmured. "If light really is a wave, what strange properties must the ether possess? It's hard to imagine! But if light is made of particles, how are double-slit interference and the bright spot of Bonaparte to be explained..."

"Let's be bold. What if the medium through which light travels isn't some kind of matter, as we usually assume, but space itself?" Napoleon suddenly said from beside them.

"Space itself? Light is actually a wave in space?" Condorcet immediately asked. "Ah, Napoleon, you have a philosophical mind. But as a scientific hypothesis, this idea very clearly lacks sufficient evidence. Science requires evidence, just like your brother's hypothesis, which at least has a mathematical model to support it. But this notion really is... What a pity. We have no usable method for studying space itself."

Napoleon's words gave Joseph quite a fright. He knew, of course, that although there was no such thing as a luminiferous ether, light wasn't a wave in space. Space could indeed undulate, but those undulations weren't light; they were gravitational waves.

This fellow... he's got quite an imagination. If I train him seriously, could I lead him astray and turn him into the emperor of physics? Joseph couldn't help thinking.