are perpetually describing between the parallels of eleven and forty-three degrees of latitude, may be accomplished by any one particle in two years and ten months. In the center of this current is situated the wide field of floating sea-weed called the grassy sea. Besides this there are branches of the Gulf-stream, which convey the fruits, seeds, and a portion of the warmth of the tropical climates to our northern shores.

The general westward motion of the South Sea, together with the south polar current, produce various watercourses in the Pacific and Indian Oceans, according as the one or the other prevails. The western set of the Pacific causes currents to pass on each side of Australia, while the polar stream rushes along the bay of Bengal: the westerly current again becomes most powerful toward Ceylon and the Maldives, whence it stretches by the extremity of the Indian peninsula past Madagascar, to the most southern point of the continent of Africa, where it mingles with the general motion of the seas. Icebergs are sometimes drifted as far as the Azores from the north pole, and from the south pole they have come even to the Cape of Good Hope. But the ice which encircles the south pole extends to lower latitudes by 10° than that which surrounds the north. In consequence of the polar current Sir Edward Parry was obliged to give up his attempt to reach the north pole in the year 1827, because the fields of ice were drifting to the south faster than his party could travel over them to the north.

As distinct currents of air traverse the atmosphere in horizontal strata, so in all probability under currents in the ocean flow in opposite directions from those on the surface; and there is every reason to believe that the cold waters, deep below the surface of the sea in the equinoctial regions, are brought by submarine currents from the poles, though it is not easy to prove their existence.

SECTION XIV.

Repulsive Force-Interstices or Pores-Elasticity-Mossotti's TheoryGravitation brought under the same law with Molecular Attraction and Repulsion-Gases reduced to Liquids by Pressure-Intensity of the Cohesive Force-Effects of Gravitation-Effects of Cohesion-Minuteness of the ultimate Atoms of Matter-Limited Height of the AtmosphereTheory of Definite Proportions and Relative Weight of Atoms-Dr. Faraday's Discoveries with regard to Affinity-Composition of Water by a Plate of Platina-Crystallization-Cleavage-Isomorphism-Matter consists of Atoms of Definite Form-Capillary Attraction.

THE Oscillations of the atmosphere and its action upon rays of light coming from the heavenly bodies, connect the science of astronomy with the equilibrium and movements of fluids, and the laws of molecular attraction. Hitherto that force has been under consideration which acts upon masses of matter at sensible distances; but now the effects of such forces are to be considered as act at inappreciable distances upon the ultimate atoms of material bodies..

All substances consist of an assemblage of material particles, which are far too small to be visible by any means human ingenuity has yet been able to devise, and which are much beyond the limits of our perceptions. Since every known substance may be reduced in bulk by pressure, it follows that the particles of matter are not in actual contact, but are separated by interstices, owing to the repulsive principle that maintains them at extremely minute distances from one another. It is evident that the smaller the interstitial spaces the greater the density. These spaces appear in some cases to be filled with air, as may be inferred from certain semi-opaque minerals and other substances becoming transparent when plunged into water; sometimes they may possibly contain some unknown and highly elastic fluid, such as Sir David Brewster has discovered in the minute cavities of various minerals, which occasionally causes these substances to explode with violence when under the hands of the lapidary, but in general they seem to our senses to be void; yet as it is inconceivable that the particles of matter should act upon one another without some means of commu

nication, there is every reason to presume that the interstices of material substances contain a portion of that subtle ethereal and elastic fluid with which the regions of space are replete.

Substances compressed by a sufficient force, are said to be more or less elastic according to the facility with which they regain their bulk or volume when the pressure is removed; a property which depends upon the repulsive force of their particles, and the effort required to compress the substance is a measure of the intensity of that repulsive force which varies with the nature of the substance.

By the laws of gravitation the particles of matter attract one another when separated by sensible distances; and as they repel each other when they are inappreciably near, it recently occurred to Professor Mossotti of Pisa, that there might be some intermediate distance at which the particles might neither attract nor repel one another, but remain balanced in that stable equilibrium which they are found to maintain in every material substance solid and fluid.

It has long been a hypothesis among philosophers that electricity is the agent which binds the particles of matter together. We are totally ignorant of the nature of electricity, but it is generally supposed to be an ethereal fluid in the highest state of elasticity surrounding every particle of matter; and as the earth and the atmosphere are replete with it in a latent state, there is every reason to believe that it is unbounded, filling the regions of space.

The celebrated Franklin was the first who explained the phenomena of electricity in repose, by supposing the molecules of bodies to be surrounded by an atmosphere of the electric fluid; and that while the electric atoms repel one another, they are attracted by the material molecules of the body. These forces of attraction and repulsion were afterward proved by Coulomb to vary inversely as the squares of the distance. The hypothesis of Franklin was reduced to a mathematical theory by pinus, and the most refined analysis has been employed by the Baron Poisson in explanation of electric phenomena. Still these philosophers were un

able to reconcile the attraction of the molecules of matter inversely as the squares of the distance as proved by Newton, with their mutual repulsion according to the same law. But Professor Mossotti has recently shown, by a very able analysis, that there are strong grounds for believing that not only the molecular forces which unite the particles of material bodies depend on the electric fluid, but that even gravitation itself, which binds world to world and sun to sun, can no longer be regarded as an ultimate principle, but the residual portion of a far more powerful force generated by that energetic agent which pervades creation.

It is true that this connection between the molecular forces and gravitation depends upon a hypothesis; but in the greater number of physical investigations, some hypothesis is requisite in the first instance to aid the imperfection of our senses. Yet, when the phenomena of nature accord with the assumption, we are justified in believing it to be a general law.

As the particles of material bodies are not in actual contact, Professor Mossotti supposes that each is encompassed by an atmosphere of the ethereal fluid; that the atoms of the fluid repel one another; that the molecules of matter repel one another, but with less intensity; and that there is a mutual attraction between the particles of matter and the atoms of the fluid. Forces which we know to exist, and which he assumes to vary inversely as squares of the distance. The following important results have been obtained by the professor from the adjustment of these three forces:

When the material molecules of a body are inappreciably near to one another, they mutually repel each other with a force which diminishes rapidly as the - infinitely small distance between the material molecules augments, and at last vanishes. When the molecules are still farther apart, the force becomes attractive. At that particular point where the change takes place, the forces of repulsion and attraction balance each other, so that the molecules of a body are neither disposed to approach nor recede, but remain in equilibrio. If we try to press them nearer, the repulsive force resists the attempt; and if we endeavor to break the body so as to

tear the particles asunder, the attractive force predominates and keeps them together. This is what constitutes the cohesive force, or force of aggregation, by which the molecules of all substances are united. The limits of the distance at which the negative action becomes positive vary according to the temperature and nature of the molecules, and determine whether the body which they form be solid, liquid, or aëriform.

Beyond this neutral point, the attractive force in creases as the distance between the molecules augments, till it attains a maximum; when the particles are more apart it diminishes; and as soon as they are separated by finite or sensible distances, it varies directly as their mass and inversely as the squares of the distance, which is precisely the law of universal gravitation.

Thus on the hypothesis that the mutual repulsion between the electric atoms is a little more powerful than the mutual repulsion between the particles of matter, the ether and the matter attract each other with unequal intensities, which leave an excess of attractive force constituting gravitation. As the gravitating force is in operation wherever there is matter, the ethereal electric fluid must encompass all the bodies in the universe; and as it is utterly incomprehensible that the celestial bodies should exert a reciprocal attraction through a void, this important investigation of Professor Mossotti furnishes additional presumption in favor of a universal ether, already all but proved by the motion of comets and the theory of light.

In aëriform fluids the particles of matter are more remote from each other than in liquids and solids; but the pressure may be so great as to reduce an aëriform fluid to a liquid, and a liquid to a solid. Dr. Faraday has reduced some of the gases to a liquid state by very great compression; but although atmospheric air is capable of a diminution of volume to which we do not know the limit, it has hitherto always retained its gaseous properties, and resumes its primitive volume the instant the pressure is removed.

If the particles approach sufficiently near to produce equilibrium between the attractive and repulsive forces, but not near enough to admit of any influence from