The Poetry of Science; or, Studies of the Physical Phenomena of Nature

by Robert Hunt

All the phenomena of life,—of the vis vitæ or vitality, are beyond human search. All the physical forces, or elements, we may examine by the test of experiment: but the principle on which sensation depends, the principle even upon which vegetable life depends, cannot be tested. Life is infinitely superior to every physical force; it holds them all in control, but is not itself controlled by them; it keeps its state sacred from human search,—the invisible hidden behind the veil of mortality.

During changes in the electrical conditions of the earth and atmosphere, vegetables give indications of being in a peculiar manner influenced by this power. It is proved by experiments that the leaves of plants are among the best conductors of electricity, and it has hence been inferred that it must necessarily be advantageous to vegetation. That vegetable growth is, equally with animal growth, subject to electricity, as one of its quickening powers, must be admitted; but all experiments which have been fairly tried with the view of stimulating the growth of plants by its agency, have given results of a negative character.[156] That a galvanic arrangement may produce chemical changes in the soil, which may be advantageous to the plant, is probable; but that a plant can be brought to maturity sooner, or be made to develope itself more completely, under the direct action of electrical excitation, appears to be one of those dreams of science which will have a place amongst the marvels of alchemy and the fictions of astrology. An attentive examination of all the conditions necessary for the satisfactory development of the plant, will render it evident, that although the ordinary electrical state of the earth and atmosphere must influence the processes of germination and vegetable growth, yet that any additional excitement must be destructive to them. The wonders wrought by electrical power are marvellous; a magic influence is exerted by it, and naturally the inquiring mind is led at first to believe that electricity is the all-powerful principle of creation; but a little reflection will serve to convince us that it is a subordinate agent, although a powerful one.

In proceeding with our examination of the phenomena which present themselves in connection with the terrestrial currents, we purposely separate magnetism from those more distinct electro-chemical agencies which play so important a part in the great cosmical operations.

Electricity, we have already stated, flows through or involves all bodies; but, like heat, it appears to undergo a very remarkable change in becoming associated with some forms of matter. We have the phenomena of magnetism when an electric current circulates through a metallic wire, and it would appear that all other bodies acquire a peculiar polar condition under the influence of this principle, which will be explained in the next chapter.

The rocks, taken as masses, will not conduct an electric current when dry: granite, porphyry, slate, and limestone, obstructing its passage even through the smallest spaces. But all the metallic formations admit of its circulating with great freedom. This fact it must, however, be remembered does not in any way interfere with the hypothesis of the existence of electricity in all bodies, in what we must regard as its latent state, from which, under prescribed conditions, it may be readily liberated. Neither does it affect the question of circulation, in relation to the great diffusion of electricity which we suppose to exist through all nature, and to move in obedience to some fixed law. We know that through the superficial strata electric currents circulate freely, whether they are composed of clay, sand, or any mixture of these with decomposed organic matter; indeed, that with any substance in a moist state they suffer no interruption.

The electricity of mineral veins has attracted much attention, and numerous investigations into the phenomena which these metalliferous formations present, have been made from time to time.[157]

By inserting into the mass of a copper lode, or vein, in situ, a metallic wire, which shall be connected with a measurer of galvanic action, a wire also from the instrument being brought into contact with another lode, an immediate effect is generally produced, showing that a current is traversing through the wires from one lode to the other, and completing the circulation probably over the dark face of the rock in which the fissures forming the mineral veins exist.[158] The currents thus detected are often sufficiently active to deflect a magnetic needle powerfully, to produce, slowly, electro-chemical decomposition, and to render a bar of iron magnetic. These currents must not be confounded with the great electrical movements around the earth. They are only to be detected in those mineral formations in which there is evidence of chemical action going on, and, the greater the amount of this chemical operation, the more energetic are the electrical currents.[159] We have, however, very good evidence that these local currents have, of themselves, many peculiar influences. It not unfrequently happens that owing to some great disturbance of the crust of the earth, a mineral vein is dislocated, and one part either sinks below, or is lifted above its original position; the fissures formed between the two being usually filled in with clay or with crystalline masses of more recent formation than the fissure itself. It is frequently found that these “cross courses,” as they are called in mining language, contain ores of a different character from those which constitute the mineral vein; for instance, in them nickel, cobalt, and silver are not unfrequently discovered. When these metals are so found, they almost invariably occur between the ends of the dislocated lode, and often take a curvilinear direction, as if they were deposited along a line of electrical force.[160]

In the laboratory such an arrangement has been imitated, and in a mass of clay fixed between the galvanic plates, after a short period a distinct formation of a mineral vein has taken place.[161] By the action, too, of weak electrical currents, Becquerel, Crosse, and others, have been successful in imitating nature so far as to produce crystals of quartz and other minerals. In addition to this evidence, in support of the electrical theory of the origin of mineral veins, it can be experimentally shown that a schistose structure may be given to clays and sandstone by voltaic action.[162]

There is often a very remarkable regularity in the direction of mineral veins: throughout Cornwall, for instance, they most commonly have a bearing from the E. of N. to the W. of S. It has hence been inferred that they observe some relation to the magnetic poles of the earth. However this may be, it is certain that the ore in any lodes which are in a direction at right angles, or nearly so, to this main line, differs in character from that found in these, so called, east and west lobes.[163]