Once his affairs were finally settled and all his tasks delegated, Su Yan set off on his return journey to the capital.
It was the fourth day of the twelfth lunar month, a little later than he had planned. The winter roads were treacherous, and even with the protection of the Embroidered Uniform Guard, the journey would take at least fifteen or sixteen days. If all went well, he would arrive in the capital by the twentieth.
Fortunately, for the return trip, he had managed to switch to a more spacious carriage. The cabin was lined with thick carpets and warmed by a brazier, keeping the wind and snow at bay behind heavy curtains.
On his way to Shaanxi, the bumpy ride had nearly shaken him apart. The way back wasn’t much better—still slow, still jarring.
After ten days of braving the wind and snow, his accompanying Embroidered Uniform Guard reported that they were now only a few dozen li from the capital—by midday, they would arrive.
Su Yan sighed in relief, slumping limply against the cushions.
Carriages in this era were slow mainly because their wooden wheels relied on a simple axle system: a pair of iron rings, one large and one small, with a generous amount of grease in between for lubrication. The friction was too great, naturally limiting speed.
The bumpiness came from the lack of any suspension.
For the sake of his suffering backside and rattling bones, Su Yan had spent much of the journey pondering ways to improve the design—something like the modern rolling axle.
The principle was simple: instead of just greasing two iron rings, introduce small iron balls between them. Their rolling motion would reduce friction during energy transfer, significantly improving mechanical efficiency.
In fact, a rudimentary version of this technology had existed as early as the Yuan Dynasty. The astronomer Guo Shoujing had used a rolling bearing structure in his armillary sphere. But for some reason, no one had ever applied the concept to wheels.
When it came down to it, many scientific advancements were like thin paper screens—poke through them, and everything became clear, leading to one breakthrough after another. But if no one made that first push, progress could stall for centuries.
Once he returned to the capital, Su Yan planned to accelerate the establishment of the Heavenly Works Academy and toss the idea of rolling bearings to the brilliant but obscure craftsmen hidden among the common folk. Let them figure out the details.
After all, he wasn’t a science student—he only knew the broad strokes. The actual manufacturing, adjustments, and refinements would be the job of professionals. Even if the process was slow and the results imperfect, any improvement would be a huge step forward.
As for shock absorption, rubber tires would be best.
The Great Ming Empire didn’t produce rubber, but the region now known as Southeast Asia—then called Jiaozhi, a vassal state of Great Ming—was covered in rubber trees.
If he explained the usefulness of rubber to Emperor Jinglong, persuading Jiaozhi to include raw rubber in its annual tribute shouldn’t be too difficult, right?
As for how raw rubber was processed into durable material, Su Yan vaguely recalled something called “vulcanized rubber.” If he remembered correctly, early methods involved sulfur.
Sulfur was abundant in Great Ming—found everywhere, used by Taoists for alchemy, commoners for fireworks, and traditional medicine for treating skin conditions.
How much sulfur to add, at what temperature, for how long—Su Yan had no clue. But that was what craftsmen were for. They could experiment step by step.
If they could develop vulcanized rubber and produce rubber tires, who cared about elasticity, heat resistance, or tensile strength? They’d still be 200 years ahead of the West.
This is far more practical than medical penicillin and has a much broader range of applications. It can be used not only for civilian purposes but also in military industries. Just imagine—if military transport vehicles were equipped with rolling bearings and rubber tires, how many times more efficient would the transportation of supplies become?
“An army marches on its stomach.” To what extent does the speed of supply transport determine the outcome of a war?
The more Su Yan thought about it, the more excited he became. He clenched his fist and struck his palm, exclaiming, “It’s decided! The first research project of the Heavenly Works Academy after its establishment will be this!”
Outside the carriage, Jinghong Zhui was riding alongside. Hearing the outburst, he called through the curtain, “My lord, do you have any orders?”
Su Yan lifted the curtain. His face, flushed pink and white from the brazier’s heat, was immediately hit by the cold wind, making him shiver. “Nothing, I was just talking to myself… Hmm? What’s that smell?”
Jinghong Zhui glanced at the sparse wild plum trees lining the roadside. “Wintersweet.”
Su Yan took a deep breath. “The floral scent seems mixed with something else… a bit pungent…” Suddenly, inspiration struck him. “It’s sulfur! I was just thinking about sulfur, and now I smell it—quicker than Cao Cao’s arrival!”
Jinghong Zhui nodded. “Yes, I do smell some sulfur. There must be a hot spring nearby.”
Gao Shuo, who had been listening in, chimed in, “You’re right! This place is called ‘Hot Dragon Valley.’ The elders say there’s a fiery dragon underground, and whenever it turns over, a hot spring appears. Even in the harshest winter, the water never freezes. Look at those wintersweet blossoms in the valley—they bloom so well because of the warm air.”
Su Yan’s interest was piqued. “What’s the temperature like? Is it good for bathing?”
Gao Shuo, seemingly familiar with the capital’s Shuntian Prefecture, answered immediately, “Most of the springs here are boiling hot—you can cook eggs in them, and the sulfur smell is strong. But there are a few with moderate temperatures, including one with no strong odor, making it perfect for bathing. The locals call it ‘Plum Immortal Spring,’ believing that an immortal once bathed there. Occasionally, they offer tributes, but no one dares to enter, fearing divine retribution.”
Su Yan laughed. “I’m not afraid. If the immortal appears, I’ll pull a Cowherd trick and hide her celestial robe! Let’s go check it out.”
By now, it was evening, and they wouldn’t reach the next post station before nightfall. They had no choice but to camp in the wild and would reach the capital’s outskirts by midday the next day. Commander Longquan gave the order for the Embroidered Uniform Guard to set up camp and start cooking.
Su Yan, accompanied by Jinghong Zhui, Gao Shuo, Chu Yuan, and ten other Embroidered Uniform Guard, informed Longquan that they would be heading to the nearby valley for a soak.
Concerned for their safety, Longquan assigned dozens of elite guards to escort them.
Following Gao Shuo’s lead, they navigated the winding mountain paths for over half an hour before arriving at the “Plum Immortal Spring,” nestled within a mountain hollow.
The natural hot spring wasn’t large—Su Yan estimated it to be less than a hundred square meters. Beside the main pool were two smaller adjacent pools. Around the spring were gray rocks, some bearing the soot stains left by villagers burning incense. Lush vegetation surrounded the area, and a few gnarled ancient wintersweet trees, at least a hundred years old, stretched their branches over the spring, scattering pale yellow petals onto the steam-covered water.
Su Yan took an instant liking to the place.
Growing up in Minzhong, he had always enjoyed soaking in hot springs. After all, Fuzhou was an ancient city of hot springs, boasting over two hundred thermal wells. Since the Jin Dynasty, the city had been famous nationwide, inspiring countless poets and scholars to compose verses about its springs. It was said to be half a city of tea fragrance, half a city of hot springs.
He tested the water temperature with his hand, then turned to look at Chu Yuan and the others.
The Embroidered Uniform Guard immediately understood his intention. Chu Yuan smiled and said, “My lord, please enjoy your bath. We will set up a windscreen around the pool.”
Su Yan waved them off. “You don’t understand the joy of an outdoor soak. If you put up a screen, it ruins the whole experience.”
Gao Shuo suggested, “How about this? We retreat a hundred paces and secure the area to prevent villagers or wild animals from disturbing you.”
Su Yan nodded. “Two hundred… no, three hundred paces.” That would be about two hundred meters—enough for dense forest cover to block any view. He didn’t want to have to worry about being seen while soaking. They were all men, but he wasn’t an exhibitionist.
Chu Yuan took his orders and led the Embroidered Uniform Guard away, quickly disappearing into the woods.
Before leaving, Gao Shuo noticed that Jinghong Zhui remained standing near the rocks, showing no intention of leaving. Annoyed, he asked sarcastically, “Why are you still here, Guard Jinghong? Didn’t you hear Lord Su’s orders?”
Jinghong Zhui, arms crossed over his sword, faced away from the spring with an impassive expression. “I’m different.”
“Oh? And how are you different?”
“I am the lord’s personal guard.”
Gao Shuo sneered. “That’s a first! I’ve never heard of a personal guard standing by even when their master bathes. What’s next? Are you going to stand by his bedside on his wedding night to hold his robes for him?”
Jinghong Zhui couldn’t be bothered with verbal sparring. He shot Gao Shuo a sharp glare, radiating an invisible pressure that forced the man to instinctively step back. Gao Shuo’s chest tightened, his breath momentarily catching, but he gritted his teeth and refused to back down.
Meanwhile, Su Yan had already removed his outer robe, draping it over a large rock. Noticing their standoff, he called out, “Are you two still here? Planning to join me for a soak? Go ahead! There are two smaller pools—you can each take one.”
Put on the spot, Gao Shuo felt embarrassed and hurriedly gestured for Jinghong Zhui to leave. “Go on! Ever heard of propriety? There are dozens of eyes watching—if you don’t leave, what will people think about you and Lord Su?”
Let them think whatever they want. What does that have to do with me? Jinghong Zhui wanted to say that but held back for Su Yan’s sake. With reluctance, he turned to leave.
Before departing, he said to Su Yan, “If you need anything, just call me—I’ll hear you.” Three hundred paces was nothing to him. With his keen senses, he could even hear the faint rustling of fabric.
With the two gone, peace returned. Su Yan stripped off the rest of his clothing, untied his hair, and slid into the steaming water with a sigh of contentment.
Jinghong Zhui, heading in the opposite direction from Gao Shuo, stopped exactly three hundred paces away. He leaped onto a snow-covered black pine, settled into position, and meditated with his sword in hand.
Not long after, a faint flute sound, barely perceptible in the cold wind, reached his ears.
Unlike an ordinary flute, this sound was sharper and more piercing, like a crane’s cry, playing a strange, intermittent melody.
This unique timbre… It was the bone flute Jiugao!
Jinghong Zhui’s eyes snapped open, a flicker of surprise passing through his gaze. Him? What was he suddenly doing here?
Jinghong Zhui frowned, suspecting that the person had come for him. If he avoided meeting, the other party would most likely persist in approaching, and if a conflict broke out, it might truly disturb Lord Su.
Better to strike first and drive him away. Besides, with dozens of elite Embroidered Uniform Guard nearby, all highly skilled, there was more than enough protection for the lord.
The bone flute’s sound grew closer. Jinghong Zhui’s expression turned cold as he pressed off the ground with his foot, sword in hand, and flew toward the mountain ridge.
His figure flickered through the twilight like a ghostly wisp of smoke, an ephemeral shadow. In no time, he had left the valley where the Plum Immortal Spring was located and arrived at a protruding, fan-shaped boulder on the mountainside.
The boulder hung over a dark abyss below. Standing at its edge was a man in gray robes, facing away, playing a slender brown bone flute carved from a crane’s bone.
His clothing was plain, his figure unremarkable, and even his long hair was simply tied into a high ponytail with a thin hemp cord, lending him a slightly youthful air.
Sensing the presence behind him, he stopped playing the flute and turned to look at Jinghong Zhui. In a soft voice, he said, “Senior Brother.”
