able to define it. These undulations are not motions in the ethereal medium itself-for that is a simple elastic expanse, capable of receiving but one impulse. It is one individual, elastic mass, allowing all bodies to move through it with ease, and closing over the track which these bodies make, so soon as they pass. It contracts in every direction to the body that is moving in it, but its particles cannot be abstracted by any process in the power of man.

Beyond our atmosphere, bodies move through this medium without noise, and for ever; and it is only in those planets where there is no atmosphere, that sounds, such as we experience, can never be heard-where sound is never heard at all.

This ethereal medium cannot move in waves, for it is one and indivisible; bodies that move in it had their places allotted to them by the Creator when he first bade them exist. But although this medium do not perform any other part than to allow of the free passage of all dense bodies, and to close over the track which they make in passing along, just as water closes over a body moving in it, yet, within the range of an atmosphere, many substances can be made larger, and cause no disturbance to the elastic medium. For instance, a small piece of caoutchouc, of one inch diameter, can be distended into a ball of three feet diameter. But this does not alter the question; this has produced no pressure on the ethereal medium, for the particles of this elastic ball first existed in this medium in the form of a gaseous compound, then in the form of inspissated vegetable juice, and finally of a solid, elastic substance.

God, in his infinite power, might, from another medium, place in our's another planet; but unless He also altered the capacity of this ethereal medium, there would be no place for it without driving out another planet of equal size with the new one far beyond the elastic medium in which all the stars and planets, of which we have any knowledge, move.

Such particles of latent matter as are necessary to the constitution of our earth, are ever present in the atmosphere, and they are rendered perceptible by the constant action that is produced by the motion of the earth, by friction, and chemical processes incident to rotary motion.

Light and heat are rendered perceptible by the united agency of two primary powers-gravity and levity-in truth, these two laws are the cause of all natural phenomena. They have various names assigned to them-such as centrifugal, centripetal, atmospheric pressure, repulsion, &c. All space, whether near the surface, or beyond the limits of the atmosphere, whether in the interstices of solid concretions, or in the hollow of the earth, is operated upon by one power-levity; and all the surfaces of dense solid particles, whether of a fluid or solid body,

fall under the control of the other-gravity. What the nature of these two powers is, can never be known, but their effects are seen and felt by all; and as they have been in operation ever since the first records of time, without any diminution of energy, it is safe to conclude that the power given them over space and matter will always be the same.

We see a solid body-ice-become a fluid by the introduction of something between its particles; this something is called heat. By adding a greater quantity of heat, the fluid is resolved to vapour; and, when we add still more heat, this vapour becomes so attenuated as to be invisible.

Another fluid-albumen-by the introduction of heat becomes a solid. Metals expand and clay contracts through the same agency. What ligament it destroys when it disunites the particles of ice-what material it adds when it renders albumen hard -what causes the expansion of metals and the contraction of clay further than that we have given the name of heat to the perceptible agent-is still a secret, and must for ever remain so.

But, although we are thus far ignorant, still we have the power and a great and wonderful power it is-of imitating all the actions, of performing all the offices, and of becoming, in reality, the agents of these two fixed laws. By pressure, friction, and concussion, we can produce both heat and cold, light and darkness; and, by the aid of these auxiliaries, we ourselves can produce all the phenomena which result from their combinations with matter. Their power is delegated to us, and, by means the most simple, we can control their excess, excite them to further action, or we can reduce them to a latent state. Our savage forefathers possessed the same privileges, and, at this lapse of time, we are as ignorant as they of the exciting

cause.

We perceive that certain bodies, whose particles have been distended by heat, are restored to their former density by the simple act of subtracting this power. What is it which enlarges the circumference of the whole mass of solid, inert matter, and renders that substance fluid which before was so dense, compact, and unyielding?

The two laws which propel all matter, setting every thing in motion, and maintaining an equilibrium throughout space, are gravity and levity. We acknowledge the existence of the former, although its immediate agents are unknown to us. The other power-levity-is but dimly seen, and is considered as acting a subordinate part; yet the agents are more familiar to us than those of gravity. It effects its object through the instrumentality of gases, and, in proportion as these gases abound, will its presence be known. It is not contended that the fixed principle itself is of an elastic nature, but that we become sensible of its

presence and power through the medium of its agents, and these agents are, undoubtedly, the gases.

Although the interstices of space and of all solid and fluid matter abound with combustible and other material particles both in a latent and perceptible state, yet no heat would be elicited if gases were present and ever ready to act. Neither could heat be made perceptible unless within the influence of an atmosphere of combustible matter, such as that which surrounds our earth. Beyond this atmosphere solar rays are cold; they convey no heat in themselves; but when they reach the combustible matter that encircles the earth, they form a union with latent heat, and thus render it perceptible.

Volatile and elastic gases circulate all perceptible and visible matter, the particles of which adhere closely to the surface of the gaseous bodies. The gases enter into the composition and organization of all inanimate and all animal and vegetable bodies, assisting to build up, repair, and destroy--even aiding in the final dispersion of the particles of these bodies, when the vital principle is extinct.

One of the primary powers-gravity—the agents of which are still but partially known to us, forces all the particles of matter to a closer union, whether they belong to solids or fluids. When near the surface and on the surface of the earth, whether the body be small or large, it is called the attraction of cohesion; but the term is inapplicable, as there is, in reality, no attraction in the case. All the impulses of gravity are compulsatory, whether operating on the whole mass of the earth at a distance, or on particles near the surface of the earth.

We are not in the habit of viewing gravity in any other light than as producing pressures and weight; we consider it as a condensing principle-as forcing all matter into contact, and reducing its size.

Every thing in the economy of nature has an opposite power to keep it in check. If the expansive effort of one power causes the sensation of heat, it may be fairly urged that the condensing or contractile efforts of its opponent will cause the sensation of cold. If the former power add levity or lightness to heated particles, the latter power will add gravity or weight to the cold particles.

It has been settled by philosophers that cold is a nonentitythe mere absence of heat-the lowest degree of heat! The name of cold is given to this nonentity, and yet we allow it neither place nor activity of any kind. Notwithstanding that the position is abandoned-if it were ever energetically maintainedthat cold is an active agent of gravity, yet it should occur to us that any thing which can consolidate a fluid by means of a property inherent in itself, and diametrically opposite to another,

must be impelled by some primary force-by one of the fixed laws. Gravity causes bodies to contract and cohere; and levity causes them to expand and separate. Do we not perceive that throughout the universe one power is always counterbalanced by another, and that these powers are essentially different in their nature? If gravity were not opposed by a force equal to itself, organic matter would soon be at an end.

Setting aside all speculations on the nature of the two fixed principles-gravity and levity-of which we can know nothing, let us examine the effects they are capable of producing through the means of their principal agents-cold and heat.

The office of cold is to contract and press together all the solid parts of a body, operating on the surfaces of the particles themselves, whether in individual atoms, or in a concrete mass.

The office of heat is to repel, or force asunder, all the particles of matter; this it accomplishes by acting altogether upon the pores or interstices of an individual atom, or upon those of large united masses.

Those substances that have passed into the last solid form which their nature is capable of assuming, come more immediately under the influence of this condensing principle-cold -which presses more readily upon their surfaces than upon those that have not arrived at this last stage. Vegetable fibre has less capacity, as the phrase is, for cold than the crystals of the alkalescent particles of this fibre; crystals, in a strict sense, being the last solid form which decomposed matter

assumes.

Minerals have a great capacity for cold, and they may be considered in the light of crystals, or concretions of bodies now unknown. We know nothing further of their history than what is presented to us in the form of ores, excepting that now and then some new elemental earth is detected in them, which may be considered as the base of the metal. What these metals were before they appeared as ores, or in solid masses, it is impossible to conjecture.

The nearer, therefore, that earthy, vegetable, animal, and fluid substances approach to a solid, concrete form, the more readily does cold operate upon them. In this compact form of solids, the agents of the calorific principle have disappeared from the interstices of these substances; not because there is nothing further on which to operate, but that they have been shut out, as it were, from the porous system by the closing or contracting of the interstices. It is, therefore, in the last stage to which a substance can arrive that cold, or gravitating pressure, has entire power over it.

It is during the gradual or sudden contact of heat, or of cold, rendered perceptible either by natural or artificial means, that

the particles of a body are elevated or depressed, expanded or condensed. If we force a given quantity of heat into a bar of iron, then the caloric principle, called levity, will predominate to the exclusion of the frigoric principle, called gravity; and the metal will continue to expand so long as it is supplied with heat, until there is a complete separation of the particles of iron. If the metal be not completely decomposed, and the exciting cause is withdrawn, it will return to nearly its former state-we say nearly, because in every operation of this kind the metal loses something. If cold were not an independent, individual power, a nonelastic body, like iron, when suddenly deprived of heat, would remain distended, nor could its volume be reduced but by mechanical means. Mechanical pressure, in fact, is but working with the same tools, using the same levers and weights employed by the gravitating principle itself. When we force two substances together by mechanical agency, we are then the agents of this primary power.

As gravity is a first principle, it pervades all space, and adheres or operates on all bodies, whether great or small, inert or animated, whether of the mineral, vegetable, or animal kingdom. Yet, independent as it is in space, acting on our own bodies likewise, the will of man can direct and control its motions when it is confined to the surface of our earth. We can accumulate its power, and apply it to depress large bodies, or small globules, or we can disperse it at pleasure.

Heat and cold are more or less perceptible as one or the other predominates; when they are equally diffused and balanced, the beneficial effects of the equilibrium are felt in an even and salutary temperature. When there is a preponderance of either, then there will be great friction amongst those particles of matter at the point where the greatest accumulations take place. In consequence, all contiguous matter is driven into new compounds and assumes new forms and qualities. It is compelled to occupy greater or smaller spaces than before, and is entirely altered in its character. We shall not stop to enquire what these results are; our purpose is first to speak of the phenomena of heat, cold, and light.

The first impulse of heat when forced from its latent state, is to propel the calorific gases from the pores and interstices of a body to the surface, whatever the dimensions of that body may be, and as far into space as the density of the matter with which they are charged will allow. In doing this it causes solids to separate, in consequence of the greater space which these gases occupy than they did before they were heated-thus forcing asunder, setting in motion, and minutely dividing the parts and particles of a body.

The lighter portions of matter, thus minutely separated, adhere