Volume II Part 19 (2/2)
[Sidenote: Physical and chemical relations of water.] The Alexandrian school had attained correct ideas respecting the mechanical properties of water as the type of liquids. This knowledge was, however, altogether lost in Europe for many ages, and not regained until the time of Stevinus and Galileo, who recovered correct views of the nature of pressure, both vertical and oblique, and placed the sciences of hydrostatics and hydrodynamics on exact foundations. The Florentine academicians, from their experiments on water inclosed in a globe of gold, concluded that it is incompressible, an error subsequently corrected, and its compressibility measured. The different states in which it occurs, as ice, water, steam, were shown to depend altogether on the amount of latent heat it contains. Out of these investigations originated the invention of the steam-engine, of which it may be said that it has revolutionized the industry of the world. Soon after the explanation of the cause of its three states followed the great discovery that the opinion of past ages respecting its elementary nature is altogether erroneous. It is not a simple element, but is composed of two ingredients, oxygen and hydrogen, as was rigorously proved by decomposing and forming it. By degrees, more correct views of the nature of evaporation were introduced; gases and vapours were found to coexist in the same s.p.a.ce, not because of their mutual solvent power, but because of their individual and independent elasticity. The instantaneous formation of vapours in a vacuum showed that the determining condition is heat, the weight of vapour capable of existing in a given s.p.a.ce being proportional to the temperature. More scientific views of the nature of maximum density were obtained, and on these principles was effected the essential improvement of the low pressure steam-engine--the apparent paradox of condensing the steam without cooling the cylinder.
In like manner much light was cast on the meteorological functions of water. It was seen that the diurnal vaporization from the earth depends on the amount of heat received, the vapour rising invisibly in the air till it reaches a region where the temperature is sufficiently low.
There condensation into vesicles of perhaps 1/50000 of an inch in diameter ensues, and of myriads of such globules a cloud is composed.
[Sidenote: Clouds and their nomenclature.] Of clouds, notwithstanding their many forms and aspects, a cla.s.sification was given--cirrus, c.u.mulus, stratus, etc. It was obvious why some dissolve away and disappear when they encounter warmer or drier s.p.a.ces, and why others descend as rain. It was shown that the drops can not be pure, since they come in contact with dust, soluble gases, and organic matter in the air.
[Sidenote: The return of water to the sea.] Sinking into the ground, the water issues forth as springs, contaminated with whatever is in the soil, and finds its way, through streamlets and rivers, back to the sea, and thus the drainage of countries is accomplished. Through such a returning path it comes to the receptacle from which it set out; the heat of the sun raised it from the ocean, the attraction of the earth returns it thereto; and, since the heat-supply is invariable from year to year, the quant.i.ty set in motion must be the same. Collateral results of no little importance attend these movements. Every drop of rain falling on the earth disintegrates and disturbs portions of the soil; every stream carries solid matter into the sea. It is the province of geology to estimate the enormous aggregate of detritus, continents washed away and new continents formed, and the face of the earth remodelled and renewed.
[Sidenote: Progress of chemistry.] The artificial decomposition of water const.i.tutes an epoch in chemistry. The European form of this science, in contradistinction to the Arabian, arose from the doctrine of acids and alkalies, and their neutralization. This was about A.D. 1614. It was perceived that the union of bodies is connected with the possession of opposite qualities, and hence was introduced the idea of an attraction of affinity. On this the discovery of elective attraction followed. Then came the recognition that this attraction is connected with opposite electrical states, chemistry and electricity approaching each other. A train of splendid discoveries followed; metals were obtained light enough to float on water, and even apparently to accomplish the proverbial impossibility of setting it on fire. In the end it was shown that the chemical force of electricity is directly proportional to its absolute quant.i.ty. [Sidenote: Attraction. The elements.] Better views of the nature of chemical attraction were attained, better views of the intrinsic nature of bodies. The old idea of four elements was discarded, as also the Saracenic doctrine of salt, sulphur, and mercury. The elements were multiplied until at length they numbered more than sixty.
[Sidenote: Theory of phlogiston.] Alchemy merged into chemistry through the theory of phlogiston, which accounted for the change that metals undergo when exposed to the fire on the principle that something was driven off from them--a something that might be restored again by the action of combustible bodies. It is remarkable how adaptive this theory was. It was found to include the cases of combustive operations, the production of acids, the breathing of animals. It maintained its ground even long after the discovery of oxygen gas, of which one of the first names was dephlogisticated air.
But a false theory always contains within itself the germ of its own destruction. The weak point of this was, that when a metal is burnt the product ought to be lighter than the metal, whereas it proves heavier.
[Sidenote: Introduction of the balance into chemistry.] At length it was detected that what the metal had gained the surrounding air had lost.
This discovery implied that the balance had been resorted to for the determination of weights and for the decision of physical questions. The reintroduction of that instrument--for, as we have seen, it had 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 quant.i.ty.
[Sidenote: Theory of oxygen, and the nomenclature.] On the ruins of the phlogistic theory arose the theory of oxygen, which was sustained with singular ability. Its progress was greatly facilitated by the promulgation of a new nomenclature in 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 att.i.tude of sovereignty to which it had been elevated, and a.s.signing 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.
[Sidenote: Present state of chemistry.] Extensive and imposing as is the structure of chemistry, it is very far from its completion. It is so surrounded by the scaffolding its builders are 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.
[Sidenote: Indestructibility of matter.] It accepts without hesitation the doctrine of the imperishability of substance; for, though the aspect of a thing may change through decompositions and recombinations, in which its const.i.tuent 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 const.i.tuent 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 pa.s.sed, whatever mutations it has undergone, whatever the force it has submitted to, its elementary const.i.tuents 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.
[Sidenote: Electrical discoveries.] Discoveries in electricity not only made a profound impression on chemistry, they have taken no insignificant share in modifying human opinion on other very interesting subjects. In all ages the lightning had been looked upon with superst.i.tious dread. The thunderbolt had long been feigned to be the especial weapon of Divinity. A like superst.i.tious 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 host, the banners and weapons of the armies of heaven. A great blow against superst.i.tion was struck when the physical nature of these phenomena was determined. As to the connexion of electrical science with the progress of civilization, what more needs to be said than to allude to the telegraph?
[Sidenote: Theories of electricity.] It is an ill.u.s.tration of the excellence and fertility of modern methods that the phenomena of the attraction displayed by amber, which had been known and neglected for two thousand years, in one-tenth of that time led to surprising results.
[Sidenote: Electrical phenomena.] First it was shown that there are many other bodies which will 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 ident.i.ty of lightning and electricity; the means of protecting buildings and s.h.i.+ps by rods; the velocity of electric movement--that immense distances can be pa.s.sed 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. [Sidenote: Voltaic electricity.] At length, when discovery seemed to be pausing, the facts of galvanism were announced in Italy. Up to this time it was thought that the most certain sign of the death 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.
[Sidenote: Results of the discovery of Galvani.] Who could have foreseen that the twitching of a frog's leg in the Italian experiments would establish beyond all question the compound nature of water, separating its const.i.tuents from 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 compa.s.s 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 friends.h.i.+p 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?
[Sidenote: Discoveries in magnetism.] As it had been with amber, so with the magnet. Its properties had lain uninvestigated for two 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 s.h.i.+ps, 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.
[Sidenote: Electro-magnetism.] Then came the Danish discovery of the relations of electricity and magnetism, ill.u.s.trated in England 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.
[Sidenote: Of light and optics.] The investigation of the nature and properties of light rivals in interest and value that of electricity.
What is this agent, light, which clothes the 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 G.o.d?
[Sidenote: Optical discoveries.] The first ascertained optical fact was probably the propagation of light in straight lines. The theory of perspective, on which the Alexandrian 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 pa.s.s 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 previously the progressive motion of light had 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 extraordinary rays given. At the same time the polarization of light by double refraction was discovered. A century later it was followed by polarisation by reflexion and single refraction, depolarization, irised rings, bright and black crosses in crystals, and unannealed or compressed gla.s.s, the connexion between optical phenomena and crystalline form, uniaxial crystals giving circular rings and biaxial oval ones, and circular and elliptical polarization.
The beautiful colours of soap-bubbles, at first mixed up with those of striated and dotted surfaces, were traced to their true condition--thickness. The determination of thickness of a film necessary to give a certain colour was the first instance of exceedingly minute measures beautifully executed. These soon became connected with fringes in shadows, and led to ascertaining the length of waves of light.
<script>