The principle of a hot air balloon is simple, with only two main challenges in its construction: the combustion system and the balloon envelope.
The first limitation is that without a pressure vessel to supply gaseous fuel, relying solely on firewood or charcoal for air heating is not only inefficient but also restricted by fuel availability, preventing long-range flight. This explains why hot air balloon principles were discovered early in history, yet hydrogen balloons were the first to be deployed in practical applications. Thus, Roland opted to abandon the combustion device, entrusting Anna with the ignition and heating.
The challenge with airbags lies in their airtightness. However, for Roland, who drew on previous experience, this issue can be easily resolved by using laminated fabric. The outermost layer of the airbag is made of wear-resistant canvas, lined with a cowhide membrane in the middle, and the inner layer consists of lightweight gauze. This layered construction ensures airtightness during stitching while also providing protection against bird pecking.
Roland deflated the balloon's base, releasing Anna's jet of black fire—warm enough to rival ordinary flames. The balloon slowly swelled, resembling a wrinkled winter melon. Designed for two riders, it had a five-meter-wide diameter, requiring twelve cattle's gut membranes and nearly a week of stitching. Such a colossal creation would have been beyond the reach of any local lord.
"Does it rely on the buoyancy from hot air to fly?" Anna asked. "I remember the book mentioned that hot air always rises." "Exactly. Hot air rising and cold air sinking are common natural phenomena. From a particle theory perspective, hotter air particles move faster and expand more easily, increasing their density as they expand. To the surrounding air, this makes them appear lighter, causing them to rise." After explaining the principle, Roland noticed that while Anna nodded in understanding, the other three looked utterly confused. This made him secretly appreciate the importance of innate talent.
As the airbag fully inflated and rose, the tow rope was slowly straightened. Roland was the first to flip into the basket, then took over from Anna as she scrambled up.
"I'm still a bit worried," the Nightingale said anxiously. "Why don't you let me try first?" "Don't worry, nothing will happen," Roland replied with a relaxed smile. "And even if something does, there's Lightning." "I'll catch them," Lightning assured him, patting his chest.
"And me, too!" Maxie patted her chest, imitating the look of a lightning bolt.
With a gentle sway, the hot air balloon lifted the basket off the ground and ascended steadily. Soon, the two crossed the castle's peak, and the town's entire panorama unfolded before them.
To Roland, such a scene was nothing new—after all, he had seen skyscrapers before. But to Anna, it was a completely different experience. Leaning over the hanging basket, she peered out, her hand gripping Roland's arm tightly, her face a mix of excitement and nervousness.
This was the first time Roland had seen her display such divine grace. Perhaps those who've never left the ground would feel a slight fear of heights when flying for the first time.
Shortly afterward, the hemp rope securing the hot air balloon beneath the basket reached its maximum tension, halting the ascent. The rope, about fifty meters long—equivalent to the height of a modern fifteen-to sixteen-story building—was then used to suspend the balloon. Roland instructed Anna to reduce the heat output, and the balloon finally stabilized in mid-air.
At first, Lightning stayed glued to the basket, but once it stabilized, he relaxed and joined Maxie in a playful chase around the hot air balloon.
From this vantage point, the castle's roof looms large, the town bustles with construction work, the Chishui River flows eastward, and the emerald farmlands along its banks stretch as far as the eye can see.
"How are you feeling?" Roland asked with a smile, only when Anna pulled her head back.
"Thank you for the gift," she exclaimed excitedly, "I can actually fly this high too." "Even higher," Roland leaned against the wicker basket's side, "if the hemp rope below were longer, we could reach ten times this distance. But the air currents get more complex at higher altitudes, making safety harder to guarantee. And this is just a basic flying machine. Once piston engines are built, ordinary people will be able to fly faster and higher than birds. And beyond that..." He looked up at the azure sky. "People could even escape this world and venture into the boundless expanse of space." "..." Anna held her breath. Her eyes sparkled, as if something was about to burst forth.
"I can't guarantee I'll fly beyond the world," Roland chuckled at her appearance, "but creating piston engines that let ordinary people soar like birds should still be achievable in my lifetime." With Anna present, processing capabilities had no longer been a bottleneck. The current limitation lay in material performance. Inferior pig iron could suffice for steam engines, wrought iron for cannons, and steel smelted from black fire for revolver firearms posed no major issues. However, internal combustion engines would likely require high-quality cast iron, cast steel, or aluminum. "Border Town's current state is all thanks to you,' Miss Anna '," Roland said. Hearing this, Anna froze. After a long pause, she leaned back and murmured, "My mother died in a fire, but instead of perishing in the smoke and flames, I became a Witch. For a long time, I believed my awakening caused the fire and deeply despised being a Witch. While imprisoned, I thought this might bring liberation, but you rescued me from the jail and taught me how to wield my powers... I never imagined flames could serve so many purposes beyond destruction and pain." Anna paused. "I should have been profoundly grateful to meet you, but now I realize my thoughts have changed. Sometimes I feel suffocated, longing for more." She climbed onto Roland's shoulders. "Even so, would you still want to employ me?" Her sapphire eyes shimmered with a glistening radiance, and the breath she exhaled left a tingling sensation on her face. Through the thin fabric of her garment, he could sense the softness of her body and the rhythmic pounding of her heart. Despite this, she did not avert her gaze—without the nightingale, she remained perpetually passionate and proactive.
"Out there is..." Before Roland could finish, Anna had already silenced him.
After they parted, he let out a soft sigh. "I want to hire you, always. Miss Anna." "Hmm." This time, he lowered his head and leaned close to her.
...
"Wait, wait," Macei chased Lightning for a moment before abruptly stopping mid-air, gazing at the empty basket. "They're gone, huh?" "What?" Lightning glanced sideways. "They just sat down." "Then you can't see the view outside?" "The view is always there, but such opportunities are rare." "Opportunities?" Macei flapped her wings and landed on Lightning's shoulder. "I don't quite understand. Should I go see them?" "No way," Lightning snatched the pigeon. "This is a sacred God ritual—no interruptions allowed." "What?" "You'll see. In moments like these, pretend you don't see. That's what my father—the greatest explorer—taught me." Lightning tossed Macei aside and crossed her arms. "Now run! I'll chase you!"