Fig. 725.—Thunderstorm and shower of ashes from Vesuvius.
A waterspout once devastated a district in the Hartz mountains of Saxony. “A long tube of vapour descended to the earth, and several times was drawn upward again; but at last it reached the ground, and travelled along at the rate of four-and-a-half miles in eight minutes, destroying everything in its way.”
On another occasion at Carcassonne in 1826, “a reddish column was seen descending to the ground, and a young man was caught up by it and dashed against a rock.” His death was instantaneous.
The cause of these whirling winds is supposed to be in the action of vertical currents of air which ascend heated, and return rapidly as cold air. The “waterspouts,” etc., are quickly formed. The tornado is a monster whirlwind like a waterspout in form, and advances at a tremendous rate—eastward as a rule. It moves in leaps and bounds, passing over some portions of the ground and descending again. The current of air is directed to the centre; the cyclone, as mentioned, has a spiral or rotatory movement.
Thunder and lightning have been, to some extent, described under the head of Electricity, but some observations may also be introduced here, as storms of that nature appertain to meteorology distinctly.
Electricity is always present in the atmosphere, and arises from evaporation and condensation as well as from plants. As the air becomes moist, the intensity of the so-called “fluid” increases, and more in winter than in summer. Clear skies are positively electric, and when large, heavy clouds are perceived in process of formation in a sky up to that time clear, a storm is almost certain to follow. These “thunder clouds,” in which a quantity of electricity exists, attract or repel each other respectively. The cloud attracts the opposite kind of electricity to that within it; and when at last a tremendous amount has been stored up in the cloud and in the air, or in another cloud, the different kinds seek each other, and lightning is the result, accompanied by a reverberation and commotion of the air strata, called thunder.
Lightning most frequently darts from cloud to cloud, but often strikes the ground, whereon and in which are good conductors, such as wet trees, metals, running water, etc. The “electric fluid” assumes different forms—“forked,” “sheet,” and “globular.” The second is perhaps the most familiar to us, and the third kind is the least known of all. There are many well-authenticated instances on record in which lightning with the form and appearance of fireballs has entered or struck houses and ships.
“Fulgarites” are vitreous tubes formed in sandy soils by the lightning in search of subterranean water-courses, for running water is a great conductor of electricity.[34] The fire-ball form of lightning has been known to enter a school-house where a number of children were, and to singe the garments of some, killing others. The ball passed out through a pane of glass, in which it bored a hole, breaking every other pane, however, in its transit. Another instance occurred in which the lightning ran about the floor of a room, and descending the stairs, exploded without doing any injury.
Lightning, like the electric current of the laboratory, will not always set fire even to inflammable objects. An electric spark can be passed through gunpowder without setting fire to it, and lightning will often shatter the object without firing it. Death by lightning is instantaneous, and in all probability quite painless; for we may argue from analogy, that as those who have been rendered insensible by lightning have had no remembrance of seeing the flash which strikes so instantaneously, nor of hearing thunder after it, it is instantaneous in its effects. Besides, the natural attitude is preserved, and the face is usually peaceful and limbs uncontorted after death by lightning.