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SECTION VII.

METEOROLOGICAL PHENOMENA RESULTING FROM THE LIGHT, AND FROM THE EARTH'S PROTOROTATION,

CHAPTER XXX.

Allusion to the concluding subject of the foregoing Chapter. Diffusion principle of Gases. Theorem and scientific evidences in favour of their expansiveness. Scriptural corroborations. The Atmosphere. Its aerial portion. Its aqueous or vaporous portion. The action of these two distinct bodies on one another, constituting the principal part of the machinery of the weather. Recapitulation of these points, and their application to elucidate the Dynamical Theory.

By the investigations which were entered into in the preceding section, we have been made aware, that the gaseous elements of the atmosphere consist of a base or radicle in union with the expansive principle, in so intimate a manner, that no means or power which the most scientific chemists have hitherto been enabled to bring to bear upon them, although a pressure equal to 800 atmospheres was applied, have been found sufficient to separate these associates. But we have yet to learn the more surprising fact, that, in a manner analogous to that in which each of these imperceptible particles may be supposed to be enveloped in a coating, or hollow sphere of expansion, their aggregate effect seems designed to produce a proportionally extended atmosphere, which surrounds the whole globe, with properties so peculiar as to indicate its almost abstraction from the otherwise universal law of gravity; for its elements expand by a law peculiar to themselves—termed "the diffusion principle"-into regions transcending the earth's surface by forty-five or fifty miles; although, strange to add, as a collective body this hollow sphere of aerial fluid possesses

considerable gravity, pressing upon the surface with a force, as already mentioned, of fifteen pounds for every square inch.

As the singular property of diffusion is that which more immediately interests us at present, by its illustrating in so striking a manner the truth of the inspired narrative, we shall attend to it exclusively. Meanwhile, as this peculiar principle has only lately been discovered, our notices respecting it will not be so full as we could otherwise have wished. The eightyseventh Theorem has reference to it, and states, "That, with respect to the oxygen and nitrogen gases of the air, although the expansive principle acts powerfully in repelling from each other the particles of the same gas, it does not act between those of different gases. That by the diffusion principle of gases,' when two are put together they will finally be arranged as if each occupied the whole space and the other was not present; the heavier being caused to ascend, and the lighter to descend. That this is the case with the gases of the atmosphere, and that there seems to exist a power acting upon permanent gases capable of counteracting, to a certain extent, the effects of the attraction of gravitation, and thereby forming an exception to what has hitherto been considered an universal law."

The following evidences will corroborate these truths :66 Strange as it may appear," says Mr. Reid, "it is now the general opinion among chemists, that the oxygen and nitrogen of the air are not in chemical union with each other, but that they are merely in a state of mechanical mixture. . . There are some reasons which might lead us to regard the oxygen and nitrogen of the air as existing in chemical union with each other. Oxygen and nitrogen, it is known, have a strong chemical attraction for each other, and are disposed to combine; the oxygen is heavier than the nitrogen, and if they are not in chemical union together, we should suppose that the oxygen would sink to the ground by itself, and the nitrogen float above it, like oil upon water; but this is not the case, for they are mixed in the same proportions at whatever distance from the ground, as Guy Lussac found in air which he collected at an elevation of nearly 22,000 feet, having ascended to that height in a balloon; also oxygen and nitrogen are present in the atmosphere exactly in the same proportions, estimated both by weight and by

measure, in which, from the laws of chemical combination, it is known they would be united, if it were a chemical union. But nevertheless, they are regarded as being merely mechanically mixed, not chemically combined; for, there is no change of form (to the solid or liquid state) as happens frequently when gases combine chemically; there is no diminution in bulk, another frequent effect of chemical union, the two gases occupying separately the same bulk as they do when forming air; generally, in effecting chemical combinations, something more is required than merely bringing the materials in contact with each other, as light, heat, or mechanical condensation, and it is well known, that gases do not combine readily on being merely mixed; but the proper proportions of oxygen and nitrogen, if merely mixed well with each other, form a gas having all the properties of air; the refractive power of the air is exactly what would be expected in a mixture of oxygen and nitrogen; there is no alteration of properties, merely a weakening, for the oxygen presents the same properties as in the uncombined state, only diminished in energy from the large quantity of nitrogen present; and lastly, there seems to be no affinity (at least a very weak one) binding the oxygen and nitrogen to each other, for the oxygen is abstracted with great ease by any substance which has an attraction for it, the nitrogen appearing to exert little or no force in retaining it. Water has the power of absorbing oxygen, though the attraction is not very great between them; yet even this weak affinity separates the oxygen from the nitrogen, for rain water contains a very large quantity of oxygen. Such are the leading arguments which may be adduced to show that the oxygen and nitrogen of the air are in a state of mechanical mixture, not chemically united.

"It has been supposed by some chemists (Berthollet and the late Dr. Murray), that although the affinity between the oxygen and the nitrogen, as they exist in the air, is not sufficient to bring them into close chemical union with each other, it still acts and produces the effect of preserving their particles near each other, and thus counteracting the effect of the attraction of gravitation, which would tend to draw all the oxygen to the ground. This explanation, it will be observed, has been given with the view of removing the difficulty, how the oxygen and nitrogen do not separate, the oxygen remaining undermost, if they are not chemically united. Some interesting experiments, however, by Dr. Dalton, of Manchester, showed that besides chemical attraction, there is another power in existence which would cause the two gases to remain mixed with each other,

and which would overcome the power of gravitation of the heavy one, which would tend to separate them. Dr. Dalton found, that two gases, however different in their specific gravities, and though they may have no chemical attraction for each other, mixed in whatever proportions in a close bottle, soon became equally diffused through one another. He made various experiments with different gases, amongst which were oxygen and nitrogen, and found, uniformly, the results to be, as he expressed in the following words: 'It appears to me as completely demonstrated as any physical principle, that whenever two or more such gases or vapours, as we have been describing, are put together into a limited or unlimited space, they will finally be arranged each as if it occupied the whole space, and the others were not present.' That is, each will be diffused or spread out through the whole space, not separating according to their respective specific gravities. This intimate intermixture of the two gases cannot be attributed to chemical attraction, for there is no chemical affinity subsisting between carbonic acid and hydrogen; it must be dependent on some other power, which, acting between gases so different in density as carbonic acid and hydrogen, causing the heavy one to ascend and the light one to descend, will produce the same effects with the oxygen and the nitrogen in the air. It is now generally considered, that it is in obedience to this law, that the oxygen and the nitrogen are mixed in air in the same proportion everywhere. Dr. Dalton supposes, that though the repulsive principle acts powerfully in repelling from each other the particles of the same gas, it does not act between those of different gases; that, therefore, a gas, by the elasticity of its particles expands into any space to which it may have access, completely disregarding any other gas which may be in that space, while the gas previously there acts in the same way, and they thus become mutually diffused through each other.

"Mr. Graham, of Glasgow, found that this expansive tendency in each gas is so great, that the intermixture takes place even when the the two gases are separated by some substance of a porous nature, as plaster of Paris, bladder, cork, or stoneware. It has been named 'THE DIFFUSION OF GASES,' and as it is an extremely curious and interesting subject, throwing light on many natural phenomena, and bringing to view a power formerly quite unknown, and capable of producing effects, which, from our previous knowledge of the laws of nature, we would have been apt to pronounce as impossible, we shall

make a few extracts from Mr. Graham's paper, which will convey some idea of this new mine which has lately been opened up in chemical philosophy.

"On repeating Doebereiner's experiment, and varying the circumstances, it appeared that hydrogen never escaped outwards by the fissure without a certain portion of air returning inwards.

"This is the peculiar phenomenon pointed out by Mr. Graham :An interchange of the two gases (the hydrogen within the jar, and the air without) taking place through the fissure. If the gases

are of unequal density, there is a consequent accumulation on the side of the heavy gas, and loss on the side of the light one. In the case of air, for instance, on the one side of the screen, 'the porous substance,' and hydrogon gas on the other, a process of exchanging one measure of the air for 3.7947 measures of hydrogen, through the apertures is commenced, and continues till the gases on both sides of the screen are in a state of uniform mixture. . . ..... When a diffusion-tube, six inches in length, was filled with hydrogen over mercury, the diffusion, or exchange of air for hydrogen, instantly commenced, through the minute pores of the stucco, and proceeded with so much force and rapidity, that within three minutes the mercury attained a height in the receiver of upwards of two inches above its level in the trough. The ascent of the water in the tube, when hydrogen is diffused, forms a striking experiment. In a diffusiontube 14 inches long, the water rises six or eight inches in as many minutes. The column of water attains in a short time its maximum height, at which, however, it is never long sustained; for, as in Doebereiner's experiment, air is all along entering mechanically from the pressure of the atmosphere through the parts by which the interior gas escapes; and after the diffusion is over, the water subsides, in the course of several hours, to the general level.

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"Such are the facts brought to light by Mr. Graham's experiments, and although our knowledge of the diffusion principle may be considered as yet in its infancy, they evince the existence of a power acting upon gases, and capable of counteracting, to a certain extent, the effects of the attraction of gravitation, forming an exception to what was formerly considered a universal law."

In conclusion, Mr. Reid states

"Our knowledge of the diffusion principle may be considered as yet merely incipient, but the discovery is one of the most interesting

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