The principle of hot air balloon is very simple, and there are only two difficulties in making it, one is the combustion device, and the other is the air bag.

The first point is that in the absence of a pressure vessel to provide gaseous fuel, relying on firewood or charcoal alone to heat the air is not only inefficient, but also cannot fly far due to fuel limitations. This is also the reason why the principle of hot air balloons was discovered very early in history, but it was the hydrogen balloon that was first put into use in actual combat. So Roland simply gave up the burning device and let Anna light the fire.

The difficulty of the airbag is its tightness, but for Roland, who has learned from the experience of his predecessors, this problem is easy to solve - just use a laminated fabric. The outermost layer of the airbag is made of hard-wearing canvas lined with a bovine intestine membrane, and the inner layer is made of lightweight gauze, so that it can be sewn together to prevent air leakage and at the same time not afraid of bird pecking.

Roland stretched out the bottom of the airbag and let Anna spew black fire into it at a temperature close to that of a normal flame, and the airbag slowly swelled up, looking like a winter melon full of wrinkles. Considering that the hot air balloon needs to carry two people into the air, the diameter of the airbag is five meters at its widest point, and the intestinal membrane of twelve cows is used, and the sewing work is nearly a week. If it weren't for the lord who ruled over a place, he might not be able to afford such a big toy.

"Does it fly with the buoyancy provided by the hot air?" asked Anna, "I remember mentioning in the book that hot air always rises upwards. ”

"That's right, it's a common natural phenomenon for hot air to rise and cold air to sink. In terms of particle theory, the hotter air balls move more intensively, have a strong ability to diffuse around, and the density becomes smaller as the volume expands. For the air that has not changed in the surrounding area, it is equivalent to becoming lighter, so it will rise. ”

After Roland finished explaining the principle, he found that except for Anna, who showed an expression of "I see", the other three were at a loss, which made him secretly sigh at the importance of talent.

When the airbag was fully inflated and floated upwards, the towing rope was slowly straightened, and Roland was the first to flip into the gondola, and then took over Anna as she climbed.

"I'm still a little worried," Nightingale said uneasily, "or you let me go up and give it a try." ”

"Trust me, nothing will happen," Roland smiled lightly, "and even if something happens, there's still lightning." ”

"I'll catch them, don't worry. Lightning patted his chest.

"And I'm goo!" said Maisie, patting her chest like lightning.

With a jolt, the hot air balloon pulls the gondola off the ground and gradually climbs upward. It didn't take long for the two of them to cross the top of the castle, and the whole picture of the town was presented to them.

Such a scene is not unfamiliar to Roland, after all, he is also a person who has seen skyscrapers, but in Anna's eyes, it is a completely new experience from the previous perspective. She leaned on the side of the hanging basket and looked out, one hand firmly grasping Roland's arm, looking excited and nervous.

This is the first time Roland has seen her show such a look, probably people who have never been far from the ground, when they fly into the sky for the first time, they will have a slight fear of heights.

After a while, the hemp rope used to hold the hot air balloon under the gondola was pulled to the limit, and the ascent stopped. The hemp rope is about 50 meters long, which is the height of a later 15 or 6 storey building. Roland tells Anna to reduce her firepower, and the balloon eventually hovers in the air.

At first, Lightning was still standing by the hanging basket, but when he saw that the basket was stable, he was relieved and played a game of chasing with Maisie around the hot air balloon.

From here, you can clearly see the roof of the castle, the town under construction, the Chishui River flowing from west to east, and the verdant farmland along the river.

"How does it feel?"

It wasn't until Anna retracted her head that Roland asked with a smile.

"Thank you for the gift," she said excitedly, "so I can fly so high." ”

"It can be higher," Roland sat down against the side wall of the rattan gondola, "If the hemp rope below is longer, it will be no problem to fly ten times the distance, but the higher you go, the more complicated the airflow becomes, and the safety will be difficult to guarantee." And this is only a rudimentary flying machine, and when a piston machine is built, ordinary people can fly faster and higher than birds, and then ...... back," he looked up at the blue sky, "People can even fly out of this world and go to the boundless space." ”

"......" Anna held her breath, her eyes sparkling with something about to come out.

"I can't guarantee that I'll fly out of the world," Roland laughed at her appearance, "but building a piston machine that allows ordinary people to fly like birds should still be able to do it in their lifetime." "In fact, with Anna, there is no bottleneck in processing capacity, and the current shortcomings lie in material properties. Inferior pig iron can be used to make steam engines, wrought iron can be used to make cannons, and steel runner firearms smelted from black fire are not a big problem, but internal combustion engines may require high-quality cast iron, cast steel, or aluminum. "It's all thanks to you that Frontier Town is what it is now, Miss Anna. ”

Hearing this, Anna was stunned. After a while, she leaned over and whispered, "My mother died in a fire, but instead of being buried in smoke and fire, I became a witch. For a long time, I thought that my awakening was the cause of the fire, and I hated myself as a witch. When I was imprisoned in prison, I thought that this might lead to liberation, but you rescued me from prison and taught me how to use my powers...... It didn't occur to me that flames could be so useful in addition to incineration and suffering. Anna paused, "I should be very satisfied to meet you, but now I find that my mind has changed, and sometimes I feel uncomfortable in my heart, and I want more." ”

She climbed up to Roland's shoulder, "Even then, do you want to hire me?"

Her lake-blue eyes sparkled and her breath blew on her face, and there was a tickling sensation. Through the thin clothes, he could feel the soft body and pounding heartbeat of the other party. Despite this, she did not avoid the direct gaze of her gaze - when there was no nightingale, she was always enthusiastic and proactive.

"There's ...... outside"

Before Roland could finish speaking, Anna had already sealed his lips.

After parting, he gasped softly, "I want to hire you, all the time." Miss Anna. ”

"Hmm. ”

This time, he took the initiative to lower his head and lean against her.

......

"Hey, wait," Maisie chased the lightning for a moment, then suddenly stopped in the air and looked at the empty hanging basket, "They're gone!"

"Huh?" Lightning glanced over, "they're just sitting down." ”

"Won't you be able to see the scenery outside?"

"The scenery can be seen at any time, but there are not many opportunities like this. ”

"Chance?" Maisie shook her wings and landed on Lightning's shoulder, "I don't understand Goo, do you want to go see them?"

"That's not going to work," Lightning said, wrapping his arms around the pigeon, "it's a sacred ritual that can't be interrupted." ”

"Goh?"

"Anyway, as you will see, at times like this, as long as you don't see it, that's what my father, the greatest explorer of all, told me. Lightning threw out Maisie and said, "Now run, I'll chase you!" )