Physics of the Terrestrial Environment, Subtle Matter and Height of the Atmosphere. Eric Chassefiere. Читать онлайн. Newlib. NEWLIB.NET

Автор: Eric Chassefiere
Издательство: John Wiley & Sons Limited
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Жанр произведения: Биология
Год издания: 0
isbn: 9781119866152
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constitution, properties, uses, different states of the atmosphere.

      The entry ATMOSPHERE in the Lexicon depicts the atmosphere as “the lower part of the Region of the Air or Ether, with which our Earth is encompassed all round; and up into which the Vapours are carried, either by Reflection from the Sun’s Heat, or by being forced up by the Subterranean Fire”. The allusion to ether must be compared to Robert Hooke’s definition of air, as we can read in the entry AIR in the Lexicon, where it is said that Hooke “seems to think the Air to be nothing else but a kind of Tincture or Solution of Terrestrial and Aqueous Particles dissolved in, and agitated by the Ether; and these Particles he supposes to be of a Saline nature.” Thus, according to Hooke, air is a mixture of ether and vapors, and therefore it does not exist as such, other than by these vapors dissolved in ether. The definition of the atmosphere is therefore consistent, since indeed we can consider that the vapors rise in the ether, as much as in the atmosphere which is its mixture with the ether. The terms “Reflection from the Sun’s Heat” are not perfectly clear, but we can verify in the entry VAPORS that it is indeed the heat of the Sun that makes water and other bodies evaporate. After this definition, the author turns to the question of the effect of atmospheric pressure, as demonstrated by Boyle through various experiments. He cited the experiment of two polished marble slabs three inches in diameter, placed in contact with each other, and that in air, required a weight of 80 pounds to separate, while in a vacuum they separated effortlessly.

      The entry AIR in the Lexicon defines air as a diaphanous (transparent), compressible and expandable (thus elastic) fluid, “covering the Earth and Sea to a great height above the highest Mountains”. As in the Encyclopédie, the following are cited as an essential component of air: (i) vapors, in the broad sense of vapors and exhalations, (ii) subtle matter, which we can assume to come from celestial bodies, as well as magnetic vapors from the Earth, (iii) finally, air in the strict sense, which can be compared to the “elementary” air described in the Encyclopédie, and whose main property is elasticity, a property that air could be the only substance to possess, the elasticity of the other bodies being perhaps due only to the air they contain. This elasticity must be understood as the reaction of air to any compression exerted by the atmosphere which, being located on top of it, weighs on it, or by any other body. Boyle suggested that the same portion of air can take up to 520,000 times more space at some times or places than at others. James Gregory calculated that a globe of air with a diameter of one inch, if it is as rare as it must be, according to the law of expansion, at the distance of half an Earth’s diameter from the Earth, would fill the entire planetary region within the sphere of Saturn (which reconciles the potentially infinite vertical extension of the atmosphere with the absence of friction encountered by the planets in their motion around the Sun).

      Although English scientists recognized the presence of subtle matter in the atmosphere, notably magnetic matter (Edmond Halley used magnetic matter to explain the aurora borealis), they nevertheless gave them less prominence than their French counterparts, with the exception, however, of Hooke, who assumed that the atmosphere resulted from the dissolution of vapors in the ether. This point of view, explicitly judged too Cartesian by the author of the ETHER entry in the Lexicon, seemed rather marginal in the English community, whose general tendency, as we will see in the course of this chapter, was to minimize the possible role of subtle matter in favor of physical explanations that favor, in particular, the role of mechanical interactions between bodies.

      The words “vapors“ and “exhalations“ were widely used in the scientific literature of the 17th and 18th centuries, and their meaning needs to be clarified. The DUF-1690 provides the following definition of vapors:

      Subtle parts of a moist body, which form a kind of smoke that poor heat raises, and cannot dissipate. Clouds and fogs form vapors that rise from the Earth. Meteors are only flaming vapors.

      This definition clearly implies that vapors are an emanation of moderately heated wet bodies. The entry FUMÉE (SMOKE) in DUF-1690 provides a definition of smoke:

      Smoke is therefore a non-transparent substance that results more or less directly from the evaporation of moisture impregnating the body. In addition, “nitrous and sulphurous exhalations are the main matter of thunder, lightning, and various other meteors that are generated in the air” (Encyclopédie, 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,