History of Lightning

Benjamin Franklin performed the first systematic, scientific study of lightning during the second half of the 18th century. Prior to that time, electrical science had developed to the point where positive and negative charges could be separated. Electrical machines could, by rubbing together two different materials, store the charges in primitive capacitors called Leyden Jars from which sparks could be generated and observed.

While others had previously noted the similarity between laboratory sparks and lightning, Franklin

was the first to design an experiment which conclusively proved the electrical nature of lightning. In

his experiment, he theorized that clouds are electrically charged, from which it follows that lightning

must also be electrical. The experiment involved Franklin standing on an electrical stand, holding an

iron rod with one hand to obtain an electrical discharge between the other hand and the ground. If

the clouds were electrically charged then sparks would jump between the iron rod and a grounded

wire, in this case, held by an insulating wax candle.

This experiment was successfully performed by Thomas Francois D'Alibard of France in May 1752

when sparks were observed to jump from the iron rod during a thunderstorm. G. W. Richmann, a

Swedish physicist working in Russia during July 1753, proved that thunderclouds contain electrical

charge, and was killed when lightning struck him.

Before Franklin accomplished his original experiment, he thought of a better way to prove his

hypothesis through the use of a kite. The kite took the place of the iron rod, since it could reach a

greater elevation and could be flown anywhere. During a Pennsylvania thunderstorm in 1752 the

most famous kite in history flew with sparks jumping from a key tied to the bottom of damp kite

string to an insulating silk ribbon tied to the knuckles of Franklin's hand. Franklin's grounded body

provided a conducting path for the electrical currents responding to the strong electric field buildup

in the storm clouds.

In addition to showing that thunderstorms contain electricity, by measuring the sign of the charge

delivered through the kite apparatus, Franklin was able to infer that while the clouds were overhead,

the lower part of the thunderstorm was generally negatively charged.

Little significant progress was made in understanding the properties of lightning until the late 19th

century when photography and spectroscopic tools became available for lightning research.

Lightning current measurements were made in Germany by Pockels (1897-1900) who analyzed the

magnetic field induced by lightning currents to estimate the current values. Time-resolved

photography was used by many experimenters during the late l9th century to identify individual

lightning strokes that make up a lightning discharge to the ground.

Lightning research in modern times dates from the work of C.T.R. Wilson who was the first to use

electric field measurements to estimate the structure of thunderstorm charges involved in lightning

discharges. Wilson, who won the Nobel Prize for the invention of the Cloud Chamber, made major

contributions to our present understanding of lightning.

Research continued at a steady pace until the late 1960's when lightning research became

particularly active. This increased interest was motivated both by the danger of lightning to

aerospace vehicles and solid state electronics used in computers and other devices as well as by the

improved measurement and observational capabilities which were made possible by advancing

technology.

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