Oxygen is heavier than air, its specific gravity being as 1.111 to 1.000. It is a supporter of combustion, and is the most powerful negative electric known; consequently always appears at the positive electrode. This gas has resisted the efforts of chemists to liquify it, though subjected to the pressure of 585 atmospheres, at the temperature of- 145° Fahrenheit. Without oxygen life could not be sustained. In it, unmixed with other gas, life flits away with greater rapidity than in common air. It is the most abundant of all elements. It is met with in every rock, rock-salt excepted; in water it forms 89 per cent., and it is an essential constituent in all organic bodies. It has been computed to constitute one-third of the

weight of the whole globe.

"Nitrogen or Azote was first observed by Rutherford, of Edinburgh, in 1772. It is lighter than atmospheric air in the proportion of 0.9727 to 1.0. It neither supports combustion nor does it sustain life, though it performs a most important part in its economy. . . . . 66 These gases are not met with in nature free, with the single exception of the air volcanoes of Turbaco in South America, which give off nitrogen. To these ingredients of the atmosphere Orfila adds electricity, light, and caloric necessary for suspending the substances in the gaseous state."*

"The results of experimental enquiry," writes Dr. Lardner, in the Cabinet Cyclopedia, "justify us in assuming, as a universal law, that by the application of a sufficient quantity of heat all solids may be converted into liquids; and by the abstraction of a corresponding quantity of heat, all liquids may be converted into solids. We have likewise seen, that by the supply of heat in sufficient quantities, all liquids may be converted into the vaporous or gaseous form; and analogy would lead us to infer, that, by the due abstraction of heat, the bodies that exist in the gaseous form might be reduced to liquids. The practical results here, however, fall short of the anticipations to which analogy leads us. There is a numerous class of bodies existing in the gaseous form, among which atmospheric air may be mentioned as the most obvious, which no means hitherto known have converted into liquids. . . . . . If a permanent gas be submitted to severe mechanical compression, its temperature will be raised, and the heat which it contains may be more easily withdrawn from it, and imparted to freezing mixtures, or

* Introduction to Meteorology, 1849, pp. 3, 6—9.

extracted by any of the usual means of exposing it to extremely low temperatures. By continually carrying on the process of compression, additional quantities of heat may be developed and withdrawn, so that at length we may succeed in reducing the quantity of heat contained in the gas to that sum of latent and sensible heat, which seems the limit of the quantity necessary to maintain the elastic form. Any further reduction would be necessarily followed by condensation.

"Means similar to these have, accordingly, been applied and succeeded, in the hands of Dr. Faraday. . . In this way, nine gases were condensed into the liquid form.

"Dr. Faraday attempted, without success, the condensation of various other gases by the same means. Oxygen, azote, and hydrogen have, it is said, been submitted to a pressure of eight hundred atmospheres, without passing into the liquid state."

*Heat, in Cab. Cyc. pp. 177-179.

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 :

"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,