As the weather warms up, the day of the second match of the Triwizard Tournament is getting closer.

The ice floes on the lake have melted, but the temperature is still frighteningly low.

Zhang Xu measured the temperature of the lake with a thermometer, and it was only 4 to 5 degrees Celsius. It is estimated that by the end of February, this temperature will not rise much.

Because of thermal expansion and contraction, the water that is heated and expanded will float on the surface of the water, and the deeper the water, the lower the temperature. Theoretically, the water temperature in the deepest part of the water will be maintained at about 4 degrees Celsius, where the water is at its densest.

The thermal conductivity of water is 26 times greater than that of air, and the average person can survive for about 60 minutes in water at 5 degrees Celsius and about 3 hours in water at 10 degrees Celsius.

The most important thing is that low temperatures will make people's hands and feet in the water numb, especially the palms and soles of people's feet, where there is no fat to keep warm, and it is most likely to cause heat loss.

In addition to this, strenuous exercise in the water can also exacerbate the loss of heat in the body.

During winter swimming, when the water temperature is maintained at 10-14 degrees Celsius, it is best for the average person to swim 100-500 meters in the water; When the water temperature is below 10 degrees Celsius, the swimming time should be very tightly controlled.

However, this is not enough time to participate in the competition.

So we had to find a way to stay active for a long time in the cold water.

On the lake, away from the castle and Durmstrang's sailboats, there is a bonfire.

Next to the campfire, a beautiful woman with long silver hair wrapped in a thick blanket in front of her, holding a glass of warm milk cocoa in her hand, is leaning against a furry giant panda to keep warm.

Fleur had just come out of the lake, and it was her first practice tonight, and she had been underwater for less than twenty minutes before she came to the surface.

Although Fleur wore a thick wetsuit, in the biting lake water, the help that the wetsuit could provide was not as great as Zhang Xu expected.

Zhang Xu and Furong, who have only dived in the Paracel Islands, do not know that under normal circumstances, they do not need to wear wetsuits when the water temperature is above 27 degrees Celsius, wet suits are required when the water temperature is below 20 degrees Celsius, and dry suits are required when the water temperature is below 10 degrees Celsius.

And the dry suit, which is suitable for use in cold water, has to be professionally trained to be used proficiently, and Fleur can't go to the training.

Therefore, Zhang Xu and Furong, who suffered a loss of no knowledge, can only find a way to solve the current problems together.

When Fleur recovered, she applied a "waterproof and moisture-proof" to her wetsuit, cast a bubble head charm on herself, and then walked towards the lake again.

Zhang Giant Panda turned back into a human form, filled the bonfire with a lot of firewood, and then placed an iron kettle next to the bonfire.

This time, half an hour later, Fleur came out of the water.

"How did you feel this time?" Zhang Xu asked.

While asking, Zhang Xu raised his wand, and a hot wind swirled around Furong, drying the newly landed Hibiscus.

"It's better than just now, but it still feels cold." Fleur replied.

Fleur rubbed her frozen hands together and sat down on the legs of the giant panda who had turned back into a leather sofa, and then put her hands close to the fire to keep warm.

"It would be nice to be able to hold a stove in the water." Fleur said as she warmed herself by the fire.

Furong's words caused Zhang Xu to think.

It's not without magic that can keep you warm, but in cold water, these magic can't be very good.

When a person is in the water, the gesture of waving the wand is easily deformed by the resistance of the water, and when chanting a spell, it is easier to pronounce it because of the water pouring into the mouth.

It's important to try to use simple spells underwater, because the simpler it is, the less likely it is to make mistakes.

Using magic to keep warm in the water not only requires a lot of mana, but also has to be spelled from time to time, which makes it easier to make mistakes.

After thinking about it for a while, Zhang Xu decided that magic was not enough to make up for it scientifically.

After changing back into a humanoid form from the black and white leather sofa, Zhang Xu took out a pack of warm babies from the treasure bag.

It took a lot of time for Zhang Xu to help Fleur open the wetsuit to warm the baby, and then it was her last practice in the water tonight.

Half an hour later, Fleur happily emerged from the water.

In the makeshift locker room conjured up with Transfiguration, Fleur changed into a wetsuit and put on a robe.

"How did you feel this time?"

Zhang Xu asked as he peeled off the skin of a hot roasted sweet potato and handed it to Hibiscus.

"I feel much better this time," Fleur said after taking the roasted sweet potato, "except for the palms and soles of her feet that are still a little cold, your body is not very cold anymore, and it is okay to stay underwater for an hour." ”

Zhang Xu nodded while nibbling on the roasted sweet potato.

"Now it's how to scout underwater." Zhang Xu said, "Some of the residents in the lake are not friendly, and it is best to avoid them. ”

"The water in the lake is not as clean as in the South China Sea, the visibility is very low, and the light is severely insufficient, so it is easy to be attacked." Zhang Xu said as he knocked open the mud shell on the outside of a chicken called Huaji.

"But if you use lighting underwater, will you attract enemies in the water?" Fleur asked, taking a fragrant chicken thigh.

"There's a risk, but other than that, it's a matter of voice, and I don't think you'll be able to learn the ropes of a dolphin in a short period of time." Zhang Xu said.

Fleur thought about it, and could only nod.

"Do you have a clue how to deal with the enemy underwater?" Zhang Xu asked.

"That's not a problem." Fleur replied confidently.

After eating and drinking by the campfire, the two put out the campfire with water and returned to Hogwarts Castle together.

Went into the water three times tonight, and it was cold enough for Hibiscus.

Although he had been roasting the fire by the bonfire for a while just now and had a hot supper, Zhang Xu still felt that Furong's hands were still very cold.

After entering the foyer of Hogwarts Castle, Zhang Xu took out the map of the living point and saw that Harry and Ron were both in the prefect's bathroom.

After the Warriors knew that Game 2 was in the water, everyone started to practice with it.

The prefectural bathroom naturally became Cedric and Ron's preference.

Zhang Xu also greeted Filch and asked him to ignore the actions of the two warriors.

So every time Zhang Xu and Furong went to the prefect's bathroom, they first used the live map to confirm whether there was anyone inside.

Zhang Xu, who planned to let Furong take a hot bath comfortably before going to bed, had to take her to the professor's bathroom.

After more than an hour, Fleur and Scarlett walked out of the professor's bathroom together, talking and laughing.

After sending off Scarlett, Fleur put down Zhang Xu, who was hanging upside down from the top of the corridor in front of the bathroom door.