EXHALAISONS (EXHALATIONS)). The moderate heat that raises this smoke cannot dissipate it, but it is added in DUF-1727 that “the Sun, through its heat, attracts the vapors; resolves, dissipates the vapors”, suggesting that these vapors can change from their smoke form to the form of a transparent substance by the action of the Sun. The Encyclopédie, in its entry VAPEURS (VAPORS), specifies this notion of elevation of a liquid body in the form of vapor:
It is the assembly of an infinite number of small bubbles of water or other liquid matter, filled with air rarefied by heat and elevated by their lightness to a certain height in the atmosphere, after which they fall back, either as rain, dew, snow, etc. The masses formed from this assembly, which float in the air, are what are called clouds.
“Bubbles of water”, as defined in the Encyclopédie in the entry BULLES (BUBBLES), are “small balls of water with air inside”, also known as “water bottles”. An explanation of the mechanism of the water bubble formation is given in the entry BOUTEILLE (BOTTLE):
Bottles or bubbles of water are expandable or compressible; in other words, they take up more or less space, depending on whether the air they contain is more or less heated, or more or less compressed: they are round, because the enclosed air also acts inside them in all directions. The coat that covers them is formed by the smallest particles of the fluid; and since these particles are very thin, and make very little resistance, the bottle will soon burst if the air expands. The mechanism of these small bottles is the same as the mechanism of those that children form with soap by blowing at the end of a wand.
Thus, these water bubbles are the air bubbles covered with a thin film of water that form on the surface of the water when an air bubble that is formed below the surface comes into contact with it before bursting, and subsequently releasing the air they contain into the atmosphere. The author of the entry makes no mention of the fact that these bubbles may come from the water particles themselves transformed into vapor, and not from the air contained in the water, as stated in the entry ÉBULLITION (BOILING) of the Encyclopédie already cited. He continues:
When a liquor is put under the container of the pneumatic machine, and the air starts to be pumped out, bottles or bubbles similar to those produced by rain rise to the surface of the liquor. These bottles are formed by the air in the liquor, which being less compressed when the air in the container begins to be pumped out, is released from between the particles of the fluid, and rises to the surface.
The same happens to a fluid that boils violently, because the air contained in it, being rarefied by the heat, seeks to expand and get out into the open, and promptly escapes to the surface of the fluid, where it forms bottles.
The author of the Encyclopédie’s entry VAPEURS (VAPORS) therefore assumes a boiling-type mechanism for their formation, during which the air bubbles, surrounded by their membrane of water, emerging on the surface of the water, rise (without bursting), because of their lightness, “to a certain height in the atmosphere”. The entry VAPORS in the Lexicon gives an almost identical definition: “Watry Exhalations raised up either by the Heat of the Sun, the Subterraneal, or any other accidental Heat, Fire.” It dwells at length on the process of raising these vapors by referring to the work of Edmond Halley in England and Guillaume Homberg in France. For Halley, “if an Atom of Water be expanded into a Shell or Bubble, whose Diameter will be ten times as great as before, such an Atom will be Specifically lighter [less dense] than Air, and will rise so long as that Flatus [the effervescent principle] or warm Spirit which first separated it from the Mass of Water, will continue to distend it to the same degree. But then that Warmth declining, and the Air growing cooler, and withal Specifically lighter; these Vapors will top at a certain Region of the Air, or else descend.” According to Halley, aqueous vapors dissolved in the air, in the same way that salt is in water, are more abundant during the day, because the Sun heats the air and increases its dissolving power, and are discharged at night in dew, because of the cooling of the atmosphere which is no longer illuminated by the Sun.
The results of Homberg’s experiments on water evaporation are then briefly presented. For him:
the Fiery or Æthereal Matter first puts the small Particles of the Water into an Agitation, and then mingles itself with it; which Mixture is what we call Vapors; this being Specifically lighter than Air, will rise in it, till it come to such an height, as that the Air is there of the same Relative Gravity with itself, and there it will swim about, till by the Motion of Winds, or other Causes, its Constitution is broken, and so the Watry Parts uniting together in greater Drops, it descends in Dew, or Rain.
The author notes the similarity between Halley’s and Homberg’s conclusions, the “flatus” of one being the “ethereal matter” of the other. But Homberg also conducted experiments of evaporation under a vacuum from a wet soil, which show that water evaporates even in a vacuum, without the help of air, since water drops form on the inner wall of the container emptied of its air (Homberg 1693). He concluded that air did not participate in the first ascensional phase of the water bubbles, since the water was projected onto the walls by the agitation of the ethereal matter. Thus, it must be assumed that the mechanism for the rise and stabilization of the water bubbles, due to their specific lightness relative to the ambient air, only occurred during the second phase.
This representation of evaporation, that is, the formation of steam, is dictated by the only directly observable form of evaporation, that is, boiling. The resulting emanations of humid bodies are again referred to as smoke, which is consistent with the conception of a cloud of particles (water bubbles) rising in the atmosphere. On the contrary, the Encyclopédie’s entry ÉVAPORATION (EVAPORATION), as we will see, concludes that a transparent vapor is being formed, which may not be air. Some scholars, as the author of the entry VAPEURS (VAPORS) says, also use vapor to refer to the fumes sent out by dry bodies, such as sulfur, but Newton and a few others used exhalations in this case. Here is how exhalations are defined in the DUF-1690:
In dogmatic terms, it is particularly said of the dry bodies and small atoms that the Earth continually pushes into the air, or that the stars attract. Vapors rise from the waters, and exhalations from the Earth: these are fatty, oleaginous and sulfurous parts that serve as matter for lightning and some other meteors.
DUF-1727 adds to “dry bodies or atoms”, “those sulfurous particles that have been separated from earthly bodies by the heat of the Sun or by the agitation of subtle matter.” The Encyclopédie defines exhalations as “smoke or vapor that is exhaled or comes out of a body and spreads in the air”, and clearly distinguishes between vapors and exhalations:
The words “exhalation” and “vapor” are usually taken interchangeably, but the authors themselves distinguish between them. They refer to as vapors the wet fumes that rise from water and other liquid bodies; and exhalations, the dry fumes that come from solid bodies, such as soil, fire, minerals, sulfur, salts, etc., which are not in contact with the air.
The exhalations, taken in the latter direction, are dry corpuscles or flows, which rise from hard, earthly bodies, either by the heat of the Sun, or by the agitation of the air, or by some other cause.
The entry EXHALATION in the Lexicon, very briefly, provides a similar definition: “whatever is raised up from the Surface of the Earth or Water by means of the heat of the Sun, that of the Subterraneal Fire, etc. such as Vapours, Mists, Fogs, etc.” It should be noted that vapors are considered here as a special case of exhalations, and that no distinction of the type proposed by the Encyclopédie is made between vapors and exhalations.
The action by which we cause the humidity of the bodies to exhale is evaporation, says the DUF-1690 in the entry EVAPORATION. For example, “Salt is formed by the evaporation of moisture, either by the heat of the sun, as in salt marshes; or by means of fire, as in places where there are salt wells.”
