  Thunder is the noise which succeeds the rush of the electrical fluid through the air. Because, by the violence of the electric force, vast fields of air are divided; great volumes of air are rarefied; and vapours are condensed, and thrown down as rain. Thunder is therefore caused by the vibrations of the air, as it collapses, and seeks to restore its own equilibrium. Because the electrical discharge takes place near the hearer, and therefore the vibrations of the air are heard in their full power. Because the electrical discharge takes place at a considerable distance, and the vibrations are affected in their course by mountains and valleys. Because, also, the forked arms of the "Lo, these are parts of his ways; but how little a portion is heard of him? but the thunder of his power who can understand?"—Job xxv. Because the electrical discharges, though violent, take place far away, and the vibrations of the air become subdued. Because the discharge of electricity takes place near the hearer. Because the discharge takes place far away, and light travels with a much greater velocity than sound. Some twenty or thirty miles, according to the direction of the wind, and the violence of the peal. The light of lightning, and its reflections, will penetrate through a distance of from a hundred and fifty to two hundred miles. Sound travels at the rate of a quarter of a mile in a second. If, therefore, the peal of thunder is heard four seconds after the flash of lightning, the discharge took place about a mile off. The pulse of an adult person beats about once in a second; therefore, guided by the pulse, any person may calculate the probable distance of the storm:— 2 beats, ½ a mile. Attention should be paid to the direction and speed of the wind, and some modifications of the calculation be made accordingly. Persons between 20 and 40 years of age should count five beats of the pulse to a mile; under 20, six beats. "The clouds poured out water; the skies sent out a sound; thine arrows also went abroad." Because of the greater evaporation, as the effect of heat; and also of the effect of heat upon the particles of all bodies. Because dry air, being a bad conductor, prevents the opposite electricities from finding their equilibrium. Because the electrical discharge destroys the vescicles of the vapours. If a number of small soap-bubbles floating in the air were suddenly broken by a violent commotion of the atmosphere, the thin films of the bubbles would form drops of water, and fall like rain. Because the equilibrium of the atmosphere is disturbed by the heat and velocity of lightning, and the condensation of vapour. Air, therefore, rushes towards those parts where a degree of vacuity or rarefaction has been produced. The name thunderbolt is applied to an electrical discharge, when the lightning appears to be developed with the greatest intensity around a nucleus, or centre, as though it contained a burning body. But there is, in reality, no such thing as a thunderbolt. "The voice of the Lord is upon the waters: the God of glory thundereth; the Lord is upon many waters."—Psalm xxix. Because they restore the equilibrium of electricity which is essential to the salubrity of the atmosphere; they intermix the gases of the atmosphere, by agitation; they precipitate the vapours of the atmosphere, and with the precipitation of vapours, noxious exhalations are taken to the earth, where they become absorbed; they also contribute largely to the formation of ozone, which imparts to the air corrective and restorative properties. Ozone is an atmospheric element recently discovered, and respecting which differences of opinion prevail. It is generally supposed to be oxygen in a state of great strength, constituting a variety of form or condition. Because careful observations have established the fact that the proportion of ozone in the atmosphere is relative to the amount of electricity. It displays an extraordinary power in the neutralisation of putrefactions, rapidly and thoroughly counteracting noxious exhalations; it is the most powerful of all disinfectants. Schonbien, the discoverer of ozone, inclines to the opinion that it is a new chemical element. Whatever it may be, there can be no doubt that it plays an important part in the economy of nature. Its absence has been marked by pestilential ravages, as in the cholera visitations; and to its excess are attributed epidemics, such as influenza. It was found, during the last visitation of cholera, that the fumigation of houses with sulphur had a remarkable efficacy in preventing the spread of the contagion. The combustion of sulphur ozonised the atmosphere; the same result occurs through the emission of phosphoric vapours; ozone is also developed by the electricity evolved by the electrical machine, and in the greater electrical phenomena of nature. The smell imparted to the air during an electric storm is identical with that which occurs in the vicinity of an electrical apparatus—it is a fresh and sulphurous odour. The opinion is gaining ground that the respiration of animals and the combustion of matter are sources of ozone, and that plants produce it when under the influence of the direct rays of the sun. It is also believed to be produced by water, when the sun's rays fall upon it. The most recent opinion respecting ozone is, that it is electrized oxygen. The subject is of vast importance, and opens another field of discovery to the pioneers of scientific truth. "The voice of thy thunder was in the heaven: the lightnings lightened the world, the earth trembled and shook."—Psalm lxvii. Magnetism is the electricity of the earth, and is characterised by the circulation of currents of electricity passing through the earth's surface. Magnetic bodies are those that exhibit phenomena which show that they are under the influence of terrestrial electricity, and which indicate the direction of the poles, or extreme points, of magnetic force. Galvanism is the action of electricity upon animal bodies, and is so called from the name of its first discoverer, Galvani. Voltaic electricity is the electricity that is developed during chemical changes, and is so called after Volta, who enlarged upon the theory of Galvani. Frictional electricity is electricity suddenly liberated under the effects of the motion, or the mechanical disturbance of bodies. Voltaic electricity is a steady flow of an electric current, arising from the gradual changes of chemical phenomena. Galvanism and Voltaism are almost identical, since the latter is founded upon, and is a development of, the former. But the term Galvanism is frequently used when speaking of the development of electricity in animal bodies. Magnetism is the electricity of the earth, and is understood to imply the fixed electricity of terrestrial bodies. "And I heard as it were the voice of a great multitude, and as the voice of many waters, and as the voice of mighty thunderings, saying Alleluia: for the Lord God omnipotent reigneth."—Rev. xix. Man knows not what electricity is; yet, by an attentive observance of its effects, he avails himself of the power existing in an unknown source, and produces marvellous results. When the Grecian philosopher, Thales, sat rubbing a piece of amber, and watching the attraction of small particles of matter to its surface, he little knew of the mighty power that was then whispering to him its offer to serve mankind. And when Franklin, with the So many great results have sprung from the careful observation of the simplest phenomena, that we should never pass over inattentively the most trifling thing that offers itself to our examination. Nature, in her revelations, never seeks to startle mankind. The formation of a rock, and the elaboration of a truth, are alike the work of ages. It was the simple blackening of silver by the sun's rays which led to the discovery of the chemical agency of light. It was the falling of an apple which pointed Newton to the discovery of the laws of gravitation. It was the force of steam, observed as it issued from beneath the lid of a kettle, that led to the invention of the steam-engine. And it is said of Jacquard, that he invented the loom which so materially aided the commerce of nations, while watching the motions of his wife's fingers, as she plied her knitting. As great discoveries spring from such small beginnings, who among us may not be the herald of some great truth—the founder of some world-wide benefaction? That the area of discovery has not perceptibly narrowed its limits, is evident from the fact that the greatest elements in nature are still mysteries to man. And though it may not be within the power of a finite being to unravel the chain of wonders that enfold the works of an infinite God,—still it is evident, from the progress which discovery has made, and from the good which discovery has done, that God does invite and encourage the human mind to contemplate the workings of Divine power, and to pursue its manifestations in every element, and in every direction. The wonderful force of electricity astonishes us all the more when we view it in contrast with that equally wonderful element, light. We have seen that light travels with a velocity of 192,000 miles in a second, but that it falls upon a delicate balance so gently, that it produces no perceptible effect. As far as we know the nature of electricity, it is even more ethereal than light; yet, while the ether of light falls harmlessly and imperceptibly—even with the momentum of a flight of ninety-five millions of miles, the ether of electricity, bursting from a cloud only five hundred yards distant, will split massive stones, level tall towers with the dust, strike majestic trees to the ground, and instantly extinguish the life of man! Why does the one ether come divested of all mechanical force, while that which seems to be even more ethereal than it, is capable of exerting the mightiest force over material things? Does it not appear that the Creator of the universe has established these paradoxes of power to testify his Omnipotence—to show to man that with Him all things are possible; and that, in the grand cosmicism of the universe, every attribute of Omnipotence has been fulfilled? "And the seventh angel poured out his vial into the air; and there came a great voice out of the temple of heaven, from the throne, saying, It is done."—Rev. xvi. Let us now consider man's relation to this Omnipotence. He sees that electricity smites the tall edifice, and observes that in doing so it displays a choice of a certain substance through which it passes harmlessly, and that its violence is manifested only when its path is interrupted. Man, taking advantage of this preference of electricity for a particular conductor, stretches out an arm of that substance, and points it upwards to the clouds; electricity |
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