Читать книгу Physics of the Terrestrial Environment, Subtle Matter and Height of the Atmosphere - Eric Chassefiere - Страница 16

What do the dictionaries of the time say about fire? The DUF-1690, in the entry FEU (FIRE), presents it as “a hot and dry element that is part of the composition of all natural bodies”, and this definition did not change in the 1727 edition. The Encyclopédie directly poses the question: “But is fire a particular matter? Or is it only the matter of bodies set in motion? This is what philosophers are divided on.” The entry points to many elements provided in the entries MATIÈRE (MATTER) and CHALEUR (HEAT). Fire is, according to the Cartesians, “the movement excited in the particles of bodies by the matter of the first element in which they swim”; according to Newton, “a heated body”; and according to others, such as Boerhaave, “a particular matter”. Pieter van Musschenbroek lent fire two specific characteristics, namely light and rarefaction (of bodies by fire). According to him, “wherever there is light, even without heat, there is fire.” He believed that it is to the matter of fire that we owe the increase in the weight of matters that burn out, as we have described. He considered that if electrical flows are fire, there are necessarily different kinds of fire. Concerning the weight of fire, we have seen that Boerhaave denied it because he attributed to the dense matter dissolved in the air the increase in weight of the calcined substances, while others, such as Lemery and Homberg, considered that this increase in weight was due to the matter of fire, which was therefore heavy. Is fire a fluid? If it has certain properties, it does not have the property of exerting pressure in all directions. The author of the entry opts for a “particular matter of fire, and present in all bodies”, as suggested by experiments on electricity. In so doing, he compares the matter of fire to electrical matter, a position that is held by Jean-Antoine Nollet, among others. After having reviewed various physical phenomena of fire, the importance of air for fire to be preserved is highlighted: “the experiment proves that fire is extinguished very quickly in the vacuum machine; and all the more quickly as the air is pumped out faster, and the container is smaller and better closed.” It is also necessary that the coarse parts of the food of the fire [“the bodies which serve to increase or maintain the fire”], such as smoke, be diverted from the fire, “a body remaining all the longer lit the less smoke it gives off, as can be seen in the wick and the peat coals.”

But it is in phosphorus that fire matter is present in the greatest quantities. The entry PHOSPHORE (PHOSPHORUS) in DUF-1690 describes phosphorus as “a matter that burns, or becomes luminous, without the need to approach a sensitive fire. It is natural, or artificial. [...] Natural phosphorus are materials that, without the help of art, at certain times become luminous, without ever having any detectable heat”, such as glowworms, or sugar when it is stored in a dark place. Natural phosphorus do not always glow, and never emit any heat. It is therefore an example of light that occurs without heat. “Artificial phosphorus are materials that become luminous by artifice, without needing to be lit by a sensitive fire.” Some artificial phosphorus burn and consume everything they come into contact with, such as animal oils produced by distillation (e.g. from urine); others have no heat, such as the Bologna stone, which, when heated beforehand, emits a faint glow in the dark. As the Encyclopédie says:

The general cause of the light of phosphorus is that the matter of fire or light is generally more abundant in this body than in others, so that the simple friction can put it into action, or that the simple action of the particles of fire or light spread in the air can awaken it. Phosphorus phenomena have much to do with electrical phenomena.

Five orders of phosphorus are described. The first order is that of bodies made into phosphorus “by the electric fluid that penetrates them”, such as glowworms, certain flies, the sting of the irritated viper, the eyes of certain live animals, certain live fish and shellfish, or even hair, or hair that has been rubbed vigorously. The second order is that of bodies that have become phosphorus “by shocks or rough rubbing that bring into play the fire contained in their interiors”, for example, stones that are rubbed vigorously against each other, or certain metal alloys that are roughly filed, or hardwoods and softwoods that are rubbed with great force. The third order is that of “bodies that have been exposed to the heat of the Sun or a violent fire, have absorbed light when they expanded, and then hold it back and let it out only little by little, or only when a soft warmth brings them closer to the state they were in when they admitted it”, bodies that today would be described as fluorescent, for example, the stone of Bologna, certain topaz, alabaster, gypsum, which the author considers that they “return the light as they received it; I mean colored, according to the color that was given to the fire that burned them.” The fourth order is that of the bodies made into phosphorus “by fermentation, dissolution, and everything that is produced by these actions, such as exhalations, effervescence, etc.” The fourth order is that of the bodies that have become phosphorus “by fermentation, dissolution, and all that is produced by them, such as exhalations, effervescence, etc.”, among which we can cite wet hay, flour, mine exhalations, meteors such as will-o’-the-wisp, falling stars, lightning or the aurora borealis. The fifth order includes “phosphorus produced by the union of a particular acid with phlogistics [i.e. elemental fire]”, such as nitrous acid, which, when ignited, forms a phosphorus, but which cannot be preserved by any known means.

These bodies, which can shine and even ignite without any external contribution in the form of heat, were considered an important class of luminous bodies at the beginning of the 18th century, as we will see with the mercurial phosphorus, that is, the glow produced by the mercury rubbing against the glass of the barometer, a phenomenon in this case of an electrical nature. The contribution of heat by friction, which characterizes certain phosphorus of the second order, and which falls into the category of mechanical heat-generating actions described by Boyle, is not recognized as such by the author of the article, for whom the origin of the light emission is internal to the phosphorus, due to a pre-existing content of igneous matter.