第73章

The transformations of Electricity into other modes of force are clearlydemonstrable. Produced by the motion of heterogeneous bodies in contact,Electricity, through attractions and repulsions, will immediately reproducemotion in neighbouring bodies. In this case a current of Electricity magnetizesa bar of soft iron; and in that case the rotation of an equipped magnet generatescurrents of Electricity. Here is the cell of a battery in which, from theplay of chemical affinities, an electric current results; and there, in theadjacent cell, is an electric current effecting chemical decomposition. Inthe conducting wire we witness the transformation of Electricity into heat;while in electric sparks and in the voltaic arc we see light produced. Moleculararrangement, too, is changed by Electricity: as instance the transfer ofmatter from pole to pole of a battery; the fractures caused by the disruptivedischarge; the formation of crystals under the influence of electric currents.

And then that, conversely, Electricity is directly generated by rearrangementof the molecules of matter, is shown when a storage-battery or accumulatoris used.

How from Magnetism the other physical forces result, must be next brieflynoted -- briefly, because in each successive case the illustrations becomein great part the obverse forms of those before given. That Magnetism producesmotion is the ordinary evidence we have of its existence. In the magneto-electricmachine a rotating magnet evolves electricity. and the electricity so evolvedmay immediately after exhibit itself as heat, light, or chemical affinity.

Faraday' s discovery of the effect of Magnetism on polarized light, as wellas the discovery that change of magnetic state is accompanied by heat, pointto further like connexions. Lastly, experiments show that the magnetizationof a body alters its internal structure; and that, conversely, the alterationof its internal structure, as by mechanical strain, alters its magnetic condition.

Improbable as it seemed, it is now proved that from Light also may proceedthe like variety of agencies. Rays of light change the atomic arrangementsof particular crystals. Certain mixed gases, which do not otherwise combine,combine in the sunshine. In some compounds light produces decomposition.

Since the inquiries of photographers have drawn attention to the subject,it has been shown that "a vast number of substances, both elementaryand compound, are notably affected by this agent, even those apparently themost unalterable in character, such as metals." And when a daguerreotypeplate is connected with a proper apparatus "we get chemical action onthe plate, electricity circulating through the wires, magnetism in the coil,heat in the helix, and motion in the needles."The genesis of all other modes of force from Chemical Action, scarcelyneeds pointing out. The ordinary accompaniment of chemical combination isheat; and when the affinities are intense, light also is produced. Chemicalchanges involving alteration of bulk, cause motion, both in the combiningelements and in adjacent masses of matter: witness the propulsion of a bulletby the explosion of gunpowder. In the galvanic battery we see electricityresulting from chemical composition and decomposition. While through themedium of this electricity, Chemical Action produces magnetism.

These facts, the larger part of which are culled from Grove's work on The Correlation of Physical Forces, show that each force is transformable,directly or indirectly, into the others. In every change Force (or Energy,as in these cases it is called) undergoes metamorphosis; and from the newform or forms it assumes, may subsequently result either the previous oneor any of the rest, in endless variety of order and combination. It is furthernow manifest that the physical forces stand not simply in qualitative correlationswith one another, but also in quantitative correlations. Besides provingthat one mode of force may be transformed into another mode, experimentsshow that from a definite amount of one, the amounts of others that ariseare definite. Ordinarily it is difficult to show this; since it mostly happensthat the transformation of any force is not into some one of the rest butinto several of them: the proportions being determined by ever-varying conditions.

But in certain cases positive results have been reached. Mr. Joule has ascertainedthat the fall of 772 lb. through one foot, will raise the temperature ofa pound of water one degree of Fahrenheit. Dulong, Petit, and Neumann, haveproved a relation in amount between the affinities of combining bodies andthe heat evolved during their combination. Between chemical action and voltaicelectricity a quantitative connexion has been established by Faraday. Thewell-determined relations between the amounts of heat generated and of waterturned to steam, or still better the known expansion produced in steam byeach additional degree of heat, may be cited in further evidence. Hence itis no longer doubted that among the several forms which force assumes, thequantitative relations are fixed. §67. Throughout the Cosmos this truth must invariably hold. Everychange, or group of changes, going on in it, must be due to forces affiliableon the like or unlike forces previously existing; while from the forces exhibitedin such change or changes must be derived others more or less transformed.

And besides recognizing this necessary linking of the forces at any timemanifested with those preceding and succeeding them, we must recognize theamounts of these forces as necessarily producing such and such quantitiesof results, and as necessarily limited to those quantities.