ages before been employed by the Saracen philosophers. who used several different forms of it-marked the epoch when chemistry ceased to be exclusively a science of quality and became one of quantity.

On the ruins of the phlogistic theory arose the theory of oxygen, which was sustained with singular Theory of oxy ability. Its progress was greatly facilitated gen, and the by the promulgation of a new nomenclature in nomenclature conformity to its principles, and of remarkable elegance and power. In the course of time it became necessary, however, to modify the theory, especially by deposing oxygen from the attitude of sovereignty to which it had been elevated, and assigning to it several colleagues, such as chlorine, iodine, etc. The introduction of the balance was also followed by important consequences in theoretical chemistry, among which pre-eminently was the establishment of the laws of combinations of bodies.

Extensive and imposing as is the structure of chemistry, it is very far from its completion. It is so Present state surrounded by the scaffolding its builders are of chemistry. using, it is so deformed with the materials of their work, that its true plan can not yet be made out. In this respect it is far more backward than astronomy. It has, however, disposed of the idea of the destruction and creation of matter. It accepts without hesitation the doctrine of the imperishability of substance;

for, though the aspect of a thing may change bility of through decompositions and recombinations, in matter. which its constituent parts are concerned, every atom continues to exist, and may be recovered by suitable processes, though the entire thing may have seemingly disappeared. A particle of water raised from the sea may ascend invisibly through the air, it may float above us in the cloud, it may fall in the rain-drop, sink into the earth, gush forth again in the fountain, enter the rootlets of a plant, rise up with the sap to the leaves, be there decomposed by the sunlight into its constituent elements, its oxygen and hydrogen; of these and other elements, acids and oils, and various organic compounds may be made: in these or in its undecomposed state it may be received in the food of animals, circulate in their blood, be essentially

concerned in acts of intellection executed by the brain, it may be expired in the breath. Though shed in the tear in moments of despair, it may give birth to the rainbow, the emblem of hope. Whatever the course through which it has passed, whatever mutations it has undergone, whatever the force it has submitted to, its elementary constituents endure. Not only have they not been annihilated, they have not even been changed; and in a period of time, long or short, they find their way as water back again to the sea from which they came.

Discoveries in electricity not only made a profound impression on chemistry, they have taken no insignificant share in modifying human opinion on other very Electrical interesting subjects. In all ages the lightning discoveries. had been looked upon with superstitious dread. The thunderbolt had long been feigned to be the especial weapon of Divinity. A like superstitious sentiment had prevailed respecting the northern lights, universally regarded in those countries in which they display themselves as glimpses of the movements of the angelic hosts, the banners and weapons of the armies of heaven. A great blow against superstition was struck when the physical nature of these phenomena was determined. As to the counexion of electrical science with the progress of civilization, what more needs to be said than to allude to the telegraph? It is an illustration of the excellence and fertility of Theories of modern methods that the phenomena of the electricity. attraction displayed by amber, which had been known and neglected for two thousand years, in one-tenth of that time led to surprising results. First it was shown Electrical that there are many other bodies which will phen mena. act in like manner; then came the invention of the electrical machine, the discovery of electrical repulsion, and the spark; the differences of conductibility in bodies; the apparently two species of electricity, vitreous and resinous; the general law of attraction and repulsion; the wonderful phenomena of the Leyden phial and the electric shock: the demonstration of the identity of lightning and electricity; the means of protecting buildings and ships by rods; the velocity of electric movement that immense distances can be passed through in an inappreciable time;

the theory of one fluid and that of two; the mathematical discussion of all the phenomena, first on one and then on the other of these doctrines; the invention of the torsion balance; the determination that the attractive and repulsive forces follow the law of the inverse squares; the conditions of distribution on conductors; the elucidation of the phenomena of induction. At length, when discovery seemed to be pausing, the facts of galvanism were announced in Italy. Up to this time it was Voltaic electhought that the most certain sign of the death tricity. of an animal was its inability to exhibit muscular contraction but now it was shown that muscular movements could be excited in those that are dead and even mutilated. Then followed quickly the invention of the Voltaic pile. Who could have foreseen that the twitching of a frog's leg in the Italian experiments would Results of the establish beyond all question the compound discovery of nature of water, separating its constituents from Galvani. one another? would lead to the deflagration and dissipation in a vapour of metals that could hardly be melted in a furnace? would show that the solid earth we tread upon is an oxide? yield new metals light enough to swim upon water, and even seem to set it on fire? produce the most brilliant of all artificial lights, rivalling if not excelling, in its intolerable splendour the noontide sun? would occasion a complete revolution in chemistry, compelling that science to accept new ideas, and even a new nomenclature? that it would give us the power of making magnets capable of lifting more than a ton, and cast a light on that riddle of ages, the pointing of the mariner's compass north and south, explain the mutual attraction or repulsion of magnetic needles? that it would enable us to form exquisitely in metal casts of all kinds of objects of art, and give workmen a means of gilding and silvering without risk to their health? that it would suggest to the evil-disposed the forging of bank notes, the sophisticating of jewelry, and be invaluable in the uttering of false coinage? that it would carry the messages of commerce and friendship instantaneously across continents or under oceans, and "waft a sigh from Indus to the pole ?"

Yet this is only a part of what the Italian experiment, carried out by modern methods, has actually done. Could there be a more brilliant exhibition of their power, a brighter earnest of the future of material philosophy?

As it had been with amber, so with the magnet. Its Discoveries in properties had lain uninvestigated for two magnetism. thousand years, except in China, where the observation had been made that its qualities may be imparted to steel, and that a little bar or needle so prepared, if floated on the surface of water or otherwise suspended, will point north and south. In that manner the magnet had been applied in the navigation of ships, and in journeys across trackless deserts. The first European magnetical discovery was that of Columbus, who observed a line of no variation west of the Azores. Then followed the detection of the dip, the demonstration of poles in the needle, and of the law of attraction and repulsion; the magnetic voyage undertaken by the English government; the construction of general variation charts; the observation of diurnal variation; local perturbations; the influence of the Aurora, which affects all the three expressions of magnetical power; the disturbance of the horary motion simultaneously over thousands of miles, as from Kasan to Paris. In the meantime, the theory of magnetism improved as the facts came out. Its germ was the Cartesian vortices, suggested by the curvilinear forms of iron filings in the vicinity of magnetic poles. The subsequent mathematical discussion was conducted upon the same principles as in the case of electricity.

Then came the Danish discovery of the relations of elecElectro-mag- tricity and magnetism, illustrated in England netism. by rotatory motions, and in France adorned by the electrodynamic theory, embracing the action of currents and magnets, magnets and magnets, currents and currents. The generation of magnetism by electricity was after a little delay followed by its converse, the production of electricity by magnetism; and thermoelectric currents, arising from the unequal application or propagation of heat, were rendered serviceable in producing the most sensitive of all thermometers.

The investigation of the nature and properties of light rivals in interest and value that of electricity. of light and What is this agent, light, which clothes the optics. earth with verdure, making animal life possible, extending man's intellectual sphere, bringing to his knowledge the forms and colours of things, and giving him information of the existence of countless myriads of worlds? What is this light which, in the midst of so many realities, presents him with so many delusive fictions, which rests the coloured bow against the cloud-the bow once said, when men transferred their own motives and actions to the Divinity, to be the weapon of God?

The first ascertained optical fact was probably the propagation of light in straight lines. The Optical distheory of perspective, on which the Alexandrian coveries. mathematicians voluminously wrote, implies as much; but agreeably to the early methods of philosophy, which were inclined to make man the centre of all things, it was supposed that rays are emitted from the eye and proceed outwardly, not that they come from exterior objects and pass through the organ of vision inwardly. Even the great geometer Euclid treated the subject on that erroneous principle, an error corrected by the Arabians. In the meantime the law of reflexion had been discovered; that for refraction foiled Alhazen, and was reserved for a European. Among natural optical phenomena the form of the rainbow was accounted for, notwithstanding a general belief in its supernatural origin. Its colours, however, could not be explained until exact ideas of refrangibility, dispersion, and the composition of white light were attained. The reflecting telescope was invented; the recognized possibility of achromatism led to an improvement in the refractor. A little Colours and previously the progressive motion of light had white light. been proved, first for reflected light by the eclipses of Jupiter's satellites, then for the direct light of the stars. A true theory of colours originated with the formation of the solar spectrum; that beautiful experiment led to the discovery of irrationality of dispersion and the fixed lines. The phenomena of refraction in the case of Iceland spar were examined, and the law for the ordinary and extra