In  other  times man didn't have more heat than the one from the sun, because he didn't know another way to warm. Therefore, there were many areas  of  the  Earth  where  one  could  not  live,  and even in the places where it was possible, sometimes, there was too much heat by day and in summer, and too cold at night and in winter.  Now, he has learned  how  to  warm  enough to live in almost all parts. For that reason, he can live in very different places that would be  uninhabitable for any other alive being of certain size. The capacity that man has to be able to generate heat to warm himself, was  one  of  the  most  important  steps  to  make  possible  its  expansion for the whole planet Earth.

The first heat that made came from an open fire that burned on the earth, As I did already said in previous chapters. During many centuries, that was the only type of heat that he knew how to make; and it continues being a very pleasant way to warm in certain occasions, as, for example, when you camps to the bleakness, in a fresh night. But, for a lot of time, the man has stopped to live outdoors. When he lived in caverns, he accustomed to light a great blaze in the entrance. Besides moving away the wild animals, the fire projected some heat inside the cavern, benefitting to those that slept. The problem was that it could not light fire inside the cavern because the smoke would have suffocated the occupants.

When the man changed caverns for houses, he didn't have another means of heating them that lighting fire in the interior. But... what one could do with it? The best possible solution was to leave a great hole in the ceiling or in the wall so that the smoke went out. Then, in the year 1100 AD. more or less, something better was gotten. It was no longer necessary to choose among the icy rooms and those in that the smoke of the fire was suffocating. With a chimney on the home, you could be quite comfortable. Certainly, it was necessary an independent fire in each room and it is hard to maintain it afire. It was, also, easy that the house caught fire. And, in the best of the cases, it lost most of the achieved heat, because more than three fourth parts escaped by the chimney.

Still today, in the villages, most of the rooms warm with a chimney home. This is a very cheerful way to heat up a room. For that reason, in the modern houses, the chimney constitutes a beautiful ornamental detail that makes happy the atmosphere, making it kinder and more intimate. Even when one obtains the heat of the radiator of vapor, it is pleasing to contemplate the splendor and the embers of the chimney, like it should please the men of  many generations behind. However in a hermetic room, one could have the enough heat to be to pleasure and also to die at the little time for oxygen lack. Because every time that a person breathes, he takes some oxygen of the air and expels some Dioxide of Carbon: and when this has lasted a lot, that air poisons. Consequently the only way to continue living is to change the air of the room, and the only way continually to be well and to feel vigorous it is to take care that it changes quickly. Because the lungs not only need of the pure air; the skin needs it much more. In a heated up room and full with people, this moves nervously, because the air is dry and fetid. And it is pleasant to leave such an atmosphere, because the skin, stiller than the lungs, likes of the fresh, humid air and in movement. In any room of three meters for four, where there is a single person, it is necessary to change the air every hour. The more people be in there, the much more often the air should be changed. In the public rooms, where a lot of people concentrate during enough time, it is necessary to use special systems to renovate the air.

Therefore, it is not enough with closing a room and heating it. That would be too simple. It is necessary to leave it more or less open and, however, to heat it. Each heating system should also take care of the ventilation. The home and the stove make it with easiness. They send a lot of air corrupted by the chimney, while pure air enters for the existent cracks around the windows and the doors. The system of hot air can provide fresh air, if this very filtrate, but not humid. And the hot water and the vapor anything makes to change the air. That of a room heated up with vapor is often very fetid and very dry..., much drier that the one that one breathes in the middle of desert.  Certainly, you can achieve that the air of the housings is healthier and more pleasant just by leaving open a window. But a modern system of heating can make something better. It can provide ventilation, to purify the air and to add him humidity. This type of heating is called air condition
 

But the fire didn't only provide light and heat for the man, it also allowed to cook food in a different way, with fire the hard meat became tender and vegetables became soft. Feeding of the first men was transformed and the culinary art was born in those former cold caves that your ancestors inhabited.        Quickly, the man discovered that fire could help to chores as important as the production of boats and weapons, a lot of time must have passed so that the man discovered that fire fused metals, giving birth to an activity that revolutionized to the human society.

.It was this way that many mechanical engines arose, among those the vapor machine that gave beginning to the industrial revolution. The domain of the fire, allowed the man to understand the complex fields of the electricity and the magnetism, knowledge that it facilitated him the development of many industrial processes, highlighting the metallurgists.
 
One of the most impressive uses that the man gives to the fire is the show that  offer us the artificial fires. We will see like they work. With the heating, certain substances produce color, effect that the pyrotechnic (art of producing fireworks) takes advantage of. we Remember that the color of the Flame many times depends on the substances that burn in her. We have this way that a rocket lights by means of a connected wick with a cartridge propeller whose size determines the height until which will go up this rocket. While this pyrotechnic cartridge is burnt, it also exploits producing diverse effects of light and noise, that that in other words it is the essence of the pyrotechnics. Two of the most popular pyrotechnic figures, like they are the " sun " and the bomb of stars they are obtained with mounted paper capsules in disks that rotate respectively in the air, and capsules of aluminum flakes that burn in some seconds.
 

But what does it give the so characteristic shine to fireworks?  Well, as it is known, many classes of fireworks contain gunpowder; that it is used to throw them and that it also provides the brilliant light in their combustion. The brilliant light is due to a finely crushed metal that it is called magnesium and that it is blended with the gunpowder to obtain the final light that offer us the fireworks. There are many important data about the magnesium. Did you knew that this same metal was used in the lamps of the photographers? When it is pure, it is of a gray one silver and much lighter that the beautiful metals.

It is not found pure in the nature because it combines very easily with other elements to form many " compounds ". Until the pieces or tapes of magnesium will burn quickly if they are lit with a match, but if the metal melts with other, mainly the aluminum, gives an alloy of great resistance and very light that is used thoroughly in the production of airplanes, of film machines and of many other things in that little weight is required.