CHAPTER III.
SECOND DAY.
ON THE ATMOSPHERE.
Composition of Atmospheric Air — Atmosphere divided into three regions — Air a fluid — Its compressibility and elasticity — Weight and pressure — Equilibrium — Transparency — Wind — Causes of Wind — Variety of Winds — Velocity of Winds — Destructive Winds — Wind under the control of God — Wind a similitude of the Holy Spirit’s operations.
On the second day God made a space or expansion, surrounding the solid earth to a certain height, called the atmosphere. This word is derived from ἀτμός and σφαῖρα, and signifies a body of vapor in a spherical form. By this name we understand the “entire mass of air which encircles all parts of the terrestrial globe, which moves with it round the sun, which touches it in all parts, ascending to the tops of its mountains, penetrating into its cavities, and incessantly floating on its waters. It is a fluid which we inhale from the first to the last moment of our existence.” The Hebrew word רקיע rakiâ, from רקע rakâ, used by Moses, (and which our translators, by following the firmamentum of the Vulgate, which is a translation of the στερεωμα, of the Septuagint, have improperly rendered firmament,) signifies to spread out as the curtains of a tent or pavilion.[53] It corresponds with those beautiful words of Isaiah, “It is he that stretcheth out the heavens as a curtain, and spreadeth them out as a tent to dwell in.” “Thus,” as a learned and pious author justly observes, “the second great production of the Almighty was the element which is next in simplicity, purity, activity, and power, to the light, (or, rather fire,) and no doubt was also used by him as an agent in producing some subsequent effects.”[54]
It is particularly deserving notice, that, after the creation of caloric, the atmosphere was the next regular production. If heat had not previously existed, could the atmosphere have been formed? The Creator, having first impressed certain principles on matter, impregnating it with repelling forces and systematical attractions, proceeded with his work according to these radical and fixed laws. One of the general laws discovered by Dr. Black, and which is laid down as a chemical axiom, is, that “Whenever a body changes its state, it either combines with caloric, or separates from caloric.” “The most probable opinion concerning the nature of caloric,” says Mr. Dalton, “is that of its being an elastic fluid of great subtlety, whose particles repel one another, but are attracted by all other bodies. Every kind of matter has its peculiar affinity to heat, by which it requires a certain portion of the fluid, in order to be in equilibrium with other bodies at a certain temperature.”[55] It is now generally supposed, adds Mr. Parkes, that the air owes its elasticity to the caloric which it contains; and, that if it could be deprived entirely of this, it would lose its elastic form. The expansibility of the air is effected by the operation of caloric: for being rarefied by heat, it occupies a larger space than otherwise it would. It is extremely probable, says Lavoisier, that air is a fluid naturally existing in a state of vapor; or, as we may better express it, that our atmosphere is a compound of all the fluids which are susceptible of the vaporous or permanently elastic state, in the usual temperature, and under the common pressure.[56]
For the discovery of the composition of atmospheric air, we are indebted to Scheele, an able chemist, born 1742, at Stralsund, in Germany, who was a member of the Academy of Stockholm, and one of the Royal Society of Medicine at Paris, and whose laborious investigations of nature have perpetuated his memory. When the nature of atmospheric air began to be understood, it was imagined that it was a mere mixture of oxygen gas and nitrogen gas; and Mr. Dalton is still of this opinion: but, says Mr. Parkes, we have now abundant reason to believe that it is a mere chemical compound; that is, that the oxygen and nitrogen form atmospheric air by a chemical union. Atmospheric air is a chemical mixture of oxygen and nitrogen rendered aërial by the expansive power of caloric: it likewise contains a portion of carbonic acid gas, which was formerly calculated at one per cent.; but Mr. Dalton has lately demonstrated that it does not amount to more than one part in a thousand.[57] Carbonic acid gas is nearly twice as heavy as common air; hence it is evident that it must combine chemically with the atmosphere, or it would be found only near the surface of the earth. If it were merely mixed with atmospheric air, its gravity would prevent it from ascending to any great height: but it is found to exist in the atmosphere at the greatest heights, (though probably not in the same proportion) as well as near the surface of the earth; which is a proof that it is not a mere mixture, but that it is chemically combined with the air. There are about 22 parts of oxygen, and 78 of nitrogen, in every 100 measures of atmospheric air, or 23 of the former and 77 of the latter, if the calculation be made by weight.[58]
Antony de Marti observes, If a few hundredth parts of oxygen only were wanting in atmospheric air, fire would lose its strength, candles would not diffuse such complete light, and animals would with difficulty separate the necessary quantity of the vivifying oxygen. On the other hand, if the atmosphere were more charged with oxygen than nitrogen, animals indeed would acquire a more free respiration; but, let us consider the activity which fire would acquire by air of superior purity. We know that, on some occasions, the least spark excites the strongest flame in a combustible body, and which increases so much as to consume it in a few moments: candles then would be no sooner lighted than they would be destroyed, without answering any other purpose than that of dazzling us for a few moments: iron would be calcined, instead of acquiring from the fire that softness necessary for transforming it into its various instruments, and which it cannot receive in a more moderate heat. Nothing would be capable of checking the progress of this destructive element, which is nourished by vital air, if this aëriform substance were not abundantly mixed with mephitic air, which serves to restrain it.
Pure atmospheric air is composed of three gaseous substances only, but is perpetually contaminated by a variety of exhalations from the earth. “The atmosphere is a vast laboratory,” says Fourcroy, “in which nature operates immense analyses, solutions, precipitations, and combinations: it is a grand reservoir, in which all the attenuated and volatilized productions of terrestrial bodies are received, mingled, agitated, combined, and separated. Notwithstanding this mixture, of which it seems impossible for us to ascertain the nature, atmospheric air is sensibly the same, with regard to its intimate qualities, wherever we examine it.” Hence, whatever may be the nature of the aërial fluid, when absolutely pure, that which we breathe, and which commonly goes under the name of air, must be considered as an exceedingly heterogeneous mixture, various at various times, and which it is by no means possible to analyze with accuracy. The whole mass of it contains a great deal of water, together with the vast collection of particles raised from all bodies of matter on the surface of the earth by effluvia, exhalations, &c., so that it may be termed a chaos of the particles of all sorts of matter confusedly mingled together. And hence it has been considered as a large chemical vessel, in which the matter of all kinds of bodies is copiously floating; and thus exposed to the continual action of that immense surface, the sun, from whence proceed innumerable operations, sublimations, separations, compositions, digestions, fermentations, putrefications, &c.
Though, in this view, the atmosphere seems to be a kind of sink or common sewer, where all the poisonous effluvia arising from putrid and corrupted matter is deposited; yet it has a wonderful facility of purifying itself, and one way or other, of depositing those vapors contained in it; so that it never becomes noxious, except in particular places, and for a short time; the general mass remaining, upon all occasions, pretty much the same.[59] The way in which this purification is effected, is different according to the nature of the vapor with which the air is loaded. Aqueous vapor ascends; and also much of that vapor arising from decayed and putrid animal and vegetable substances, (and which, by some modern philosophers, is called phlogiston, attaching itself to the aqueous vapor,) ascends along with it; and probably descends again with the rain; whence the fertilizing qualities of rain-water above those of any other: while another part is absorbed by vegetables; for the phlogistic vapor is probably the food for plants. But sulphureous, acid, and metalline exhalations, produced principally by volcanos; vapors, arising from houses where lead and other metals are smelted; descend, in consequence of their specific gravity, and suffocate and spread destruction around them, poisoning not only animals, but vegetables also. From all these, the air seems not capable of purifying itself, otherwise than by winds, or by letting them subside by their superior gravity, till they are absorbed either by the earth or water, according as it is their nature to unite with one or other of these elements. Of this kind also seem to be the vapors which are properly called pestilential. The contagion of the plague itself seems to be of a heavy, sluggish nature, incapable of rising in the air, but attaching itself to the walls of houses, bed-clothes, and wearing apparel. Hence, scarcely any constitution of the atmosphere can dispel these noxious effluvia; nor does it seem probable that pestilential distempers ever cease until the contagion has operated so long, and been so frequently communicated from one to another, that, like a ferment much exposed to the air, it becomes vapid, communicates a milder infection, and at last loses its strength altogether.