sustain the planet's organization, though it may, in the first instance, deluge it. Should a comet be attracted towards a planet possessing such a temperature as the earth, we should probably obtain evidence of its approach or not, according to its magnitude. When within a certain distance of the globe, unless it were directly incident, it would revolve when at a certain degree of proximity around it, producing immense tides in the ocean in consequence of its attraction of aggrega tion as well as gravitation, and would begin to be distilled over as mist, clouds, and showers. An unusual rain would increase to a certain maximum, and then gradually "assuage;" and when the whole nebula was received by the earth, the sky would clear up and permit the sun to shine upon the deluged planet. Comets and some nebulæ, then, are merely the mists, hailstones, and raindrops of the ethereal expanse, analogous to those of the earth's atmosphere.

Pure water, when kept in an insoluble vessel, is a very permanent body. But this can only be said of it when its electrical state remains undisturbed. One of the most curious features connected with its structure, is the ease with which it may be separated into two bodies capable of being developed in a singularly easy manner by the two electricities. Every particle, which is at once strongly electro-positive in one region, and electro-negative in another, can at once be resolved into two, one of which is very highly positive, and the other very highly negative. Suppose, then, that two wires, from the poles of a galvanic axis, are brought near each other, and that a particle of water is placed in the focus, it is solicited opposite ways. In virtue of being positive, it is drawn to the negative. pole; and in virtue of being negative, it is drawn to the positive pole. It immediately fulfils the conditions of its state, by giving one particle of hydrogen to the negative pole, upon which the remaining five particles immediately resolve themselves into the only symmetrical form that is possible, without a great change of place, and which is also the most highly negative of all bodies, and satisfies most perfectly the demands of the positive pole. Thus, from the destruction of every

particle of water, one of hydrogen seeks to the negative pole, and one (b, Fig. 37), evidently of very different structures and properties, to the positive. If there is no body in the way, these bodies may be seen escaping in bubbles through the water, but the hydrogen only can be collected pure. The other, when prevented from uniting with the hydrogen, immediately on coming into the region of the radiant medium, attracts an atom into its pole, and has no longer such an excessive affinity for hydrogen, but they may exist together for a long time without uniting. If this body has not thus its pole occupied by radiant matter, as soon as it arrives in a region of electrical equilibrium, it constantly unites to hydrogen, when both are simultaneously disengaged, and a particle of water results. Hence the decomposition of water into the two free gases now considered is probably only a chemical experiment, and never occurs in nature to any great extent. Water is, indeed, frequently resolved into the form in which a particle of hydrogen is drawn out, the electro-negative form being on its pole (c, Fig. 39), and the form prevented from returning to the common state of water, by either pole being engaged with some other body. It is to be observed of water in this form, when the engagement is at the hydrogerent poles, that it possesses the property of discharging true colours, or such as arise from a chromatic axis. The naked pole probably receives the extreme atom of the chromatic axis, which of course is completely destroyed, for the edges of the extreme atoms that are left must be parallel,—an arrangement on which polarity and the resulting colour cannot take place. We shall find that this arrangement obtains in deutoxide of hydrogen, in sulphurous acid, and the aqueous solution of chlorine.

Water is decomposed when it is placed between the poles of an acid and a metal, with whose calx the acid unites. These bodies, the metal and acid, are in opposite galvanic states, and they are further aided in decomposing water, by the metal's demand for an electro-negative form, and the acid's for the resulting calx. The common metals, as will be after

wards seen, are parasitic forms conformable to this electronegative body, and having a vehement affinity for it. Hence they exert a disposing influence to induce the water into a state, both as to form and electricity, consecutive to themselves, that is, into the state of this body, while the hydrogen is suffered to escape, and is replaced by the acid. It could not be asserted, however, that in the action of such an acid as oil of vitriol upon a metal, every particle of water suffered resolution into these two forms. There cannot easily be less hydrogen than the just quantity, but it is very probable, that some particles of water, when the quantity of calx generated is great, may be wholly resolved into hydrogen. To this, the presence of much electro-negative matter would dispose, and the demand of the metal for such matter might not wholly prevent it. In such experiments, then, there will probably be found a small excess of hydrogen. Oil of vitriol, and muriatic acid, would be more apt to split water into hydrogen in this way than nitric acid; for these two acids insert themselves into its poles, and exert a stronger influence upon three particles of hydrogen, than upon the other three, but nitric acid cannot find access to the poles of a particle of water.

The resolution of water into these two bodies, can only take place to a considerable extent where the frustular may unite with some other body. When the pole of this form is naked, the hydrogen, newly disengaged, is again attracted, as soon as both are removed from the decomposing focus. Hence water at the bottom of the ocean, though decomposed into these two bodies by galvanic energy there, would be recom posed before the gaseous elements had gained the surface; and therefore, if this electro-negative body be found in the air in great quantities, it cannot be obtained by the decompo sition of the waters at great depths, into these two forms.

When a vigorous galvanic state is induced in a quantity of water, besides the gases evolved, certain substances make their appearance, of an alkaline and acid nature, which has excited much of the interest of experimentalists. Of these, none is more curious than soda. Sir H. Davy obtained nota

ble quantities of soda from pure water contained in an agate cup, which did not yield any on analysis. He satisfied himself, however, that it was derived from no other source than the cup, because he did not obtain any, when the water was acted on in gold vessels. But the silica of the agate has a great affinity for soda, and would dispose to its evolution according to well known and acknowledged principles, while gold has no such affinity. Hence, though soda was not developed in the gold, it does not follow that it was not developed in the agate. It is scarcely to be expected, however, that sodium should have been generated in notable quantities in such small experiments: it is, indeed, one of the forms of most simple structure and easy development; but it would require very unequivocal evidence, before we should assume that it has been produced in the laboratory of the chemist.

The two electrical resultants of decomposed water that have thus been elicited, are the most active and most perpetually recurring of all bodies. The one, by itself, in various arrangements, produces some most interesting substances, while the other is a constituent of almost every natural body.

OF OXYGEN.

WHEN a particle of hydrogen is removed from one of water, the spendyloid form which results (Fig. 8 and Fig. 37) is named Oxygen; its atomic weight is 10; its form is a pentagonal prism, the opposite edges of the base and summit being in a transverse position to each other, and the prism being terminated on both aspects by a concave or negative pentagonal pyramid. Like water, its centre, which is absolutely cold, is exposed; and its form is so ill adapted for sustaining a state of considerable vibration, that its specific heat must be very small, and its attractive energy and weight consequently great. The facets, supposing the five contituent hydrogens to retain their form, cannot be perfectly in contact, in consequence of the inability of ten atoms of matter, or five particles

of hydrogen, to apply themselves to each other perfectly in this position. We may indeed suppose that matter is soft enough to yield a little, so as to produce symmetry and solidity. It is more probable, however, that the angles only yield a little, and that the particle is, consequently, in a state of constraint, which will aid in explaining the ease with which it changes form, and becomes water when a particle of hydrogen is supplied to it. Its electrical state is the most highly equatorial, or negative, of any body, and its external edges and concave pentagonal poles are conformable to a great many substances. Hence it is never met with in nature in a free state, nor can it be insulated in the laboratory, for it always affects the aëriform state, and, thus exposed to the incidence of radiant matter, an atom perches in its pole as hydrogen does, and the oxygen becomes vital air. Its properties are consequently unknown. It obtained the name of oxygen from the belief that it was the principle which generated acidity; but it is essentially a part of the fixed alkalis, as well as most other bodies, whether acid or alkaline; and some of the strongest acids, such as spirit of salt and vinegar, derive their acidity from the union of hydrogen with their base. The Greek radical of the name, however, expresses also activity, and is therefore still descriptive of oxygen, though, as is well known, it cannot now be regarded as the acidifying principle.

Oxygen is very abundantly diffused in nature; it constitutes a large part of all siliceous, calcareous, and ferruginous stones and rocks: it is abundant in animal and vegetable bodies, and constitutes rather more than a fifth part of the atmosphere. There, however, it exists in the only form in which it can be obtained by the chemist, viz.,

Vital or Empyreal Air.-When we consider the unipolar electrical state of a particle of oxygen, and the susceptibility of an atom of the radiant medium contiguous to its pole, to have an opposite state induced upon it, we will not hesitate for a moment to believe, that, as soon as oxygen mingles with radiant matter, it will unite with it as it does with hydrogen,

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