ELECTRICITY.
Discovery of Electrical Force—Diffused through all Matter—What is Electricity?—Theories—Frictional Electricity—Conducting Power of Bodies—Hypothesis of two Fluids—Electrical Images—Galvanic Electricity—Effects on Animals—Chemistry of Galvanic Battery—Electricity of a Drop of Water—Electro-chemical Action—Electrical Currents—Thermo-Electricity—Animal Electricity—Gymnotus—Torpedo—Atmospheric Electricity—Lightning Conductors—Earth’s Magnetism due to Electrical Currents—Influence on Vitality—Animal and Vegetable Development—Terrestrial Currents—Electricity of Mineral Veins—Electrotype—Influence of Heat, Light, and Actinism on Electrical Phenomena.
If a piece of amber, electrum, is briskly rubbed, it acquires the property of attracting light bodies. This curious power excited the attention of Thales of Miletus; and from the investigations of this Grecian philosopher we must date our knowledge of one of the most important of the natural forces—Electricity.
If an inquiring mind had not been led to ask why does this curious natural production attract a feather, the present age, in all probability, would not have been in possession of the means by which it is enabled to transmit intelligence with a rapidity which equals the poet’s dream of the “swift-winged messengers of thought.” To this age of application a striking lesson does this amber teach. Modern utility would have regarded Thales as a madman. Holding a piece of yellow resin in his hand, rubbing it, and then picking up bits of down, or catching floating feathers, the old Greek would have appeared a very imbecile, and the cui bono generation would have laughed at his silly labours. But when he announced to his school that this amber held a soul or essence, which was awakened by friction, and went forth from the body in which it previously lay dormant, and brought back the small particles floating around it, he gave to the world the first hint of a great truth which has advanced our knowledge of physical phenomena in a marvellous manner, and ministered to the refinements and to the necessities of civilisation. Each phenomenon which presents itself to us, however simple it may appear to be, is an outward expression of some internal truth, the interpretation of which is only to be arrived at by assiduous study, but which, once discovered, directs the way to new knowledge, and gives to man a great increase of power. There is no truth so abstract that it will not find its useful application, and every example of the ministration of Physical Science to the purposes of humanity is an evidence of the value of abstract study, and a reply to the utilitarian in his own language.
Electricity appears to be diffused through all nature; and it is, beyond all doubt, one of the most important of the physical forces, in the great phenomena of creation. In the thunder-cloud, swelling with destruction, it resides, ready to launch its darts and shake the earth with its explosions: in the aërial undulations, silent and unseen, it passes, giving the necessary excitement to the organisms around which it floats. The rain-drop—the earth-girdling ocean—and the ringing waters of the hill-born river, hold locked this mighty force. The solid rocks—the tenacious clays which rest upon them—the superficial soils—and the incoherent sands, give us evidence of the presence of this agency; and in the organic world, whether animal or vegetable, the excitement of electrical force is always to be detected.
In the solar radiations we have perhaps the prime mover of this power. In our atmosphere, when calm and cloudless, a great ocean of light, or when sombre with the mighty aspect of the dire tornado, we can constantly detect the struggle between the elements of matter to maintain an equilibrium of electrical force.
Diffused throughout matter, electricity is ever active; but it must be remembered that although it is evidently a necessary agent in all the operations of nature, that it is not the agent to which everything unknown is to be referred. Doubtless the influence of this force is more extensive than we have yet discovered; but that is an indolent philosophy which refers, without examination, every mysterious phenomenon to the influence of electricity.
The question, what is electricity? has ever perplexed, and still continues to agitate, the world of science. While one set of experimentalists have endeavoured to explain the phenomena they have witnessed, upon the theory that electricity is a peculiar subtile fluid pervading matter, and possessing singular powers of attraction and repulsion, another party find themselves compelled to regard the phenomena as giving evidence of the action of two fluids which are always in opposite states; while again, electricity has been considered by others as, like the attraction of gravitation, a mere property of matter.[136] Certain it is, that in the manifestations of electrical phenomena we have, as it appears, the evidence of two conditions of force; but of the states of positive or negative, of vitreous or resinous electricity, we have a familiar explanation in the assumption of some current flowing into or out of the material body,—of some principle which is ever active in maintaining its equilibrium, which, consequently, must act in two directions, and always exhibit that duality which is a striking characteristic of this subtile agent. It is a curious, and it should be an instructive fact, that each of the three theories of electricity is capable of proof, and has, indeed, been most ably supported by the rigorous analysis of mathematics. When we remember that some of the most enlightened investigators of this and the past age have severally maintained, in the most able manner, these dissimilar views, we should hesitate before we pronounce an opinion upon the cause or causes of the very complicated phenomena of electrical force.
Although we discover, in all the processes of nature, the manifestations of this principle or force in its characteristic conditions, it will be necessary, before we regard the great phenomena, to examine the known sources from which we can most readily evoke the mighty power of electricity. If we rub a piece of glass or resin, we readily render this agent active; these substances appear, by this excitement, to become surrounded by an attractive or a repellent atmosphere. Let us rub a strip of writing paper with Indian rubber, or a strip of Gutta Percha with the fingers, in the dark, and we have the manifestation of several curious phenomena. We have a peculiar attracting power; we have a luminous discharge in the shape of a spark; and we have very sensible evidence of muscular disturbance produced by applying the knuckle to the surface of the material. In each case we have the development of the same power.
Every substance in nature is an electric, and, if so disposed that its electricity may not fly off as it is developed, we may, by friction, manifest its presence, and, indeed, measure its quantity or its force. All bodies are not, however, equally good electrics; shell-lac, amber, resins, sulphur, and glass, exhibiting more powerfully the phenomena of frictional or mechanical electricity, than the metals, charcoal, or plumbago. Solid bodies allow this peculiar principle to pass along them also in very different degrees. Thus electricity travels readily through copper and most other metals, platinum being the worst metallic conductor. It also passes through living animals and vegetables, smoke, vapour, rarified air, and moist earth; but it is obstructed by resins and glass, paper when dry, oils, and dry metallic oxides, and in a very powerful manner by Gutta Percha.[137]