PROTECTION FROM LIGHTNING FURNISHED BY A CLOSED CONDUCTOR.
It is not necessary that the brass cylinder should be insulated. To vary the experiment, I will now connect it with the earth by a chain; you will observe that the effect is precisely the same as before. Flash after flash passes while the machine continues in action; the outside pith balls fly about violently, being charged and discharged alternately; the inside pith balls remain all the time at rest. Thus you see clearly that, if you were sitting inside such a metal chamber as this, or covered with a complete suit of metal armor, you would be perfectly secure during a thunderstorm, whether the chamber were electrically connected with the earth or insulated from it.
Practical Rules.—But it rarely happens, when a thunderstorm comes, that an iron hut or a complete suit of armor is at hand, and you will naturally ask me what you ought to do under ordinary circumstances. First, let me tell you what you ought not to do. You ought not to take shelter under a tree, or under a haystack, or under the lee of a house; you ought not to stand on the bank of a river, or close to a large sheet of water. If indoors, you ought not to stay near the fireplace, or near any of the flues or chimneys; you ought not to stand under a gasalier hanging from the ceiling; you ought not to remain close to the gas pipes or water-pipes, or any large masses of metal, whether used in the construction of the building, or lying loosely about.
The necessity for these precautions is sufficiently evident from the principles I have already put before you. You want to prevent your body from becoming a link in that broken chain of conductors which, as we have seen, the electric discharge between earth and cloud is likely to follow. Now a tree is a better conductor than the air; and your body is a better conductor than a tree. Hence, the lightning, in choosing the path of least resistance, would leave the air to pass through the tree, and would leave the tree to pass through you. A like danger would await you if you stood under the lee of a haystack or of a house.
The number of people who lose their lives by taking refuge under trees in thunderstorms is very remarkable. As one instance out of many, I may cite the following case which was reported in the Times, July 14, 1887: “Yesterday the funeral of a negress was being conducted in a graveyard at Mount Pleasant, sixty miles north of Nashville, Tennessee, when a storm came on, and the crowd ran for shelter under the trees. Nine persons stood under a large oak, which the lightning struck, killing everyone, including three clergymen, and the mother and two sisters of the girl who had been buried.”
Again, every large sheet of water constitutes practically a great conductor, which offers a very perfect medium of discharge between the earth round about and the cloud. Therefore, when a thundercloud is overhead, the sheet of water is likely to become one end of the line of the lightning discharge; and if you be standing near it, the line of discharge may pass through your body.
When lightning strikes a building, it is very apt to use the stack of chimneys in making its way to earth, partly because the stack of chimneys is generally the most prominent part of the building, and partly because, on account of the heated air and the soot within the chimney, it is usually a moderately good conductor. Therefore, if you be indoors, you must keep well away from the chimneys; and for a similar reason, you must keep as far as you can from large masses of metal of every kind.
Having pointed out the sources of danger which you must try to avoid in a thunderstorm, I have nearly exhausted all the practical advice that I have at my command. But there are some occasions on which it may be possible, not only to avoid evident sources of danger, but to make special provision for your own security. Thus, for example, in the open country, if you stand a short distance from a wood, you may consider yourself as practically protected by a lightning conductor. For a wood, by its numerous branches and leaves, favors very much a quiet discharge of electricity, thus tending to suppress altogether the flash of lightning; and if the flash of lightning does come, it is much more likely to strike the wood than to strike you, because the wood is a far more prominent body, and offers, on the whole, an easier path to earth. In like manner, if you place yourself near a tall solitary tree, some twenty or thirty yards outside its longest branches, you will be in a position of comparative safety. If the storm overtake you in the open plain, far away from trees and buildings, you will be safer lying flat on the ground than standing erect.
In an ordinary dwelling house, the best situation is probably the middle story, and the best position in the room is in the middle of the floor; provided, of course, that there is no gasalier hanging from the ceiling above or below you. Strictly speaking, the middle of the room would be a still safer position than the middle of the floor; and nothing could be more perfect than the plan suggested by Franklin, to get into “a hammock, or swinging bed, suspended by silk cords, and equally distant from the walls on every side, as well as from the ceiling and floor, above and below.” An interesting case has been recently recorded, by a resident of Venezuela, which illustrates in a remarkable way the excellence of this advice. “The lightning,” he says, “struck a rancho—a small country house, built of wood and mud, and thatched with straw or large leaves—where one man slept in a hammock, another lay under the hammock on the ground, and three women were busy about the floor; there were also several hens and a pig. The man in the hammock did not receive any injury whatever, while the other four persons and the animals were killed.”[37]
But, as I can hardly hope that many of you when the thunderstorm actually comes will find yourselves provided with a hammock, I would recommend, as more generally useful, another plan of Franklin’s, which is simply to sit on one chair in the middle of the floor and put your feet up on another. This arrangement will approach very nearly to absolute security if you take the further precaution, also mentioned by Franklin, of putting a feather bed or a couple of hair mattresses under the chairs.[38]