Newfoundland, then bending to the east it flows past the Azores and Canary islands, till it joins the great westerly current of the tropics about latitude 21° north. According to M. de Humboldt this great circuit of 3800 leagues, which the waters of the Atlantic 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 centre 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 water-courses 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 towards Ceylon and the Maldives, whence it stretches by the extremity of the Indian peninsula past Madagascar to the most northern 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.

MOS

INTERSTICES OR PORES. ELASTICITY. SOTTI'S THEORY. GRAVITATION 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 ATMOSPHERE. THEORY OF DEFINITE PROPORTIONS AND RELATIVE WEIGHT OF ATOMS. DR. FARADAY'S DISCOVERIES WITH REGARD TO AFFINITY.-COMPOSITION OF WATER BY A PLATE OF PLATINA.-CHRYSTALLISATION. 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 communication, 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 Corfu, 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 afterwards 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 unable 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 connexion 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 encom