Nature Wonders of Electricity and Light
Electricity produces an infinity of changes in the natural world. It may be artificially elicited or called forth by friction; or by contact of certain substances and the action attendant on this contact. In the one case it is termed ordinary, and in the other case voltaic or galvanic electricity.
All substances are supposed to contain a certain portion of electricity, and if by friction or other means any substance acquires more electrical action than it would naturally possess, it is said to be positively electrified; and if less, it is said to be negatively electrified. Substances when positively electrified attract or draw toward them other substances which are in a state of negative electricity, or even those which are in a natural state, but will repel or force from them substances which are positively electrified. The sudden contact of bodies in an opposite state of electricity is attended with vivid light called the “electric spark,” and accompanied by explosion and shock.
Earth and Air Form Nature’s Electric Battery
The earth is always in a state of positive electricity, and the air when pure in a state of negative electricity. Atmospheric air, however, is subject to incessant variations, and hence its “electrical equilibrium” or natural electrical state is subject to be disturbed. This equilibrium will be restored when an explosion has taken place, and thus it is that in peculiar states of the atmosphere thunder storms act a beneficial part in restoring the air to a normal condition. The intensity of electrical action is greater during the day than at night and also in summer than in winter; and diminishes from the equator to the poles.
Electricity is perpetually effecting great changes in the earth’s crust, and in very many instances acts on the principal of voltaic electricity, the action in such cases being produced by long-continued currents.
Lightning—The Electrical Discharge in the Heavens
Lightning is the dazzling light produced by an electrical discharge passing between clouds which are oppositely electrified, or between the clouds and the earth. Lightning flashes have been distinguished as zigzag or chain lightning, sheet and globular lightning.
The first has the aspect of a sharply defined chain of fire, and moves at the rate of 250,000 miles per second. Its zigzag course is attributed to the resistance of the air, condensed in the passage of the electrical discharge, which is sufficient to turn it aside frequently in the direction of less resistance.
Sheet lightning includes the expanded flashes which occur during a storm, and the heat lightning, seen on summer evenings, when no clouds are visible, which is supposed to be the reflection of a storm taking place below the horizon.
Globular lightning is seen on rare occasions, when the electrical discharge takes the form of a ball of fire, and descending with less rapidity, is visible for several seconds. In certain conditions of the atmosphere, globes or spires of electrical light, called St. Elmo’s fire, are seen tipping the extremities of bodies in contact with the earth, like church spires, or masts of ships.
All the conditions which give rise to electrical excitement in the atmosphere are much more intense in warm than in cold latitudes; hence the thunder storms of the tropical regions greatly exceed, both in frequency and in violence, those of temperate and cold climates.
The Aurora Borealis, or Northern Lights
This phenomenon is frequently observed in the northern heavens. It occurs in many forms, but the most common is that of a luminous arch whose summit is in the magnetic meridian of the place of observation, and from which vivid flashes of light dart towards the zenith. A like phenomenon in the southern heavens is denominated the Aurora Australis. Auroras are most frequent and brilliant in the polar regions, and diminish in intensity towards the equator.
Rainbows, Halos and Coronas
Rainbows are arches of prismatic colors, formed by the reflection of rays of light from within drops of water. The rays, which are refracted in entering the drops, are reflected from their posterior surfaces, and again refracted as they re-enter the air, the colors being separated by their unequal refrangibility.
Halos and coronas are circles of prismatic colors which, in certain states of the atmosphere, surround the Sun and the Moon.
Halos are supposed to be occasioned by the presence, in the atmosphere, of small ice crystals which act as minute prisms, decomposing and refracting the light which passes through them.
Coronas are seen when a light mist is floating in the air, and are supposed to be formed by reflection from the external surface of the globules of vapor.
Colors of the Sky and Clouds
The azure tint of the cloudless sky is due to the decomposition and refraction of light, as it passes through layers of air successively increasing in density. The blue and violet, being more refrangible than other colors of the solar spectrum, are diffused through the atmosphere; and being reflected from its particles, they impart to it their own color.
The clouds, floating in the atmosphere, absorb the more refrangible rays, and reflect the less. At sunrise and sunset, when the light traverses the greatest depth of atmosphere, all the colors are absorbed except the red and the yellow; and these, being deflected from the particles of vapor, produce the brilliant coloring of sunrise and sunset.
The Mystifying Mirage
The mirage is an optical phenomenon in which images of distant objects are seen, reflected beneath, or suspended in the heavens above. Occasionally, also, objects are seen double, being repeated laterally instead of vertically.
The mirage is caused by the refraction and reflection of light as it passes from denser to rarer strata of air. It is most frequent in arid plains, where the soil, exposed to the burning rays of the sun, becomes intensely heated, and, in consequence, the strata of air near the ground are less dense than those above.
In this case rays of light passing from any distant object, as a tree, to the ground, are refracted more and more towards the horizontal, until finally they are reflected from a horizontal layer of the heated air, and reach the eye from beneath. Then an image of the object is seen as if mirrored in the tranquil waters of a lake.
THE MAGNIFICENT CURTAINS OF LIGHT THAT FORM THE AURORA BOREALIS