Twenty Thousand Miles a Second

Man's ideas have changed markedly since the days when he thought the gods hurled lightning like spears and caused thunder by driving their metal chariots across the sky. Today, lightning has been reduced to a mere electrical unbalance, resulting when a preponderance of positive electrical charges accumulate at one place while a preponderance of negative charges accumulate somewhere else. This happens with the formation of thunderclouds, when strong upward air currents carry positive charges to the top of the cloud, while negative charges accumulate in the lower regions of the cloud. Meanwhile, positive charges are attracted to the earth's surface just below the cloud, and, when the unbalance becomes too great, lightning results.

Kipling referred to lightning as the time when the "heavens balance their volt accounts." As for thunder-its cause is not nearly as spectacular as the old chariot wheel theory. Its modern explanation is simple. The air in the path of a lightning flash is heated and expands rapidly. Then, as the heated air cools and begins to contract, more air rushes in to fill the space, and the resulting disturbance smites the ear as sharp or rolling thunder. Most lightning flashes are from cloud to cloud and only a small percentage of the total reaches the earth. Cloud-to-cloud spark channels may be five to ten miles long or longer, while those to the ground may be four or five miles long.

Lightning is not a rare thing. Scientists have estimated that 44,000 thunderstorms occur on the earth every day, with some 360,000 lightning flashes an hour. The strokes travel at a speed of about 20,000 miles a second. One investigator, F.W. Peek, Jr., of General Electric Company, has assigned the following values to an average bolt of lightning: voltage, 100,000,000; current, 100,000 amperes; energy, four kilowatt-hours; time, a few millionths of a second. The Buffalo Niagara Electric Company's lightning recorder during a 44-minute midnight thunderstorm June 29 and 30 reported the greatest number of lightning flashes per storm, 1945. During that time 354 lightning flashes were recorded, an average of eight a minute for the entire period.

Scientists have learned many things about lightning, but they can neither control it nor anticipate the exact place it will strike. Despite its great power, scientists have no illusions of harnessing lightning and putting it to work. Its occurrence is so unpredictable and its appearance so fleeting that such attempts would be futile. There is scarcely enough usable electric energy in a terrifying bolt of lightning to supply current for an electric iron. Man can produce electricity for his needs, and his main concern with lightning is to devise better ways of protecting his power lines, buildings and other possessions from it.