Benjamin Franklin - Kostenloses Hörbuch

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THE THUNDER GIANT

A few years before his retirement, Franklin, on a visit to Boston, attended a display of electrical tricks given by a Dr. Adam Spencer of Scotland. There is no record of the nature of these “electrical tricks.” Franklin commented later that Dr. Spencer was no expert and that they were imperfectly performed. Since he had never seen anything of the sort before, he was “surpris’d and pleased.”

That sparks could be produced by friction had been known since ancient times. Little more was known about electricity until, in the first part of the eighteenth century, a young Frenchman, Charles François du Fay, identified two different types of electricity: vitreous, produced by rubbing glass with silk; resinous, produced by rubbing resin with wool or fur. Such frictional electricity was brief-lived. Sparks flashed and were gone, and that was the end of it.

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Was there any way in which electric charges could be preserved from the rapid decay which they underwent in the air? Around 1747 two scientists were working independently on this problem—E. C. von Kleist of Pomerania and Pieter van Musschenbroek of the University of Leyden. Within a few months of each other, they had found a method of storing electricity in a container. The Leyden jar, this container was named. It was the first electrical condenser.

In one experiment Musschenbroek suspended a glass phial of water from a gun barrel by a wire which went down through a cork in the phial a few inches into the water. The gun barrel, hanging on a silk rope, had a metallic fringe inserted into the barrel which touched an electrically charged glass globe. A friend who was watching him, a man named Cunaeus, happened to grasp the phial with one hand and the wire with another. Immediately he felt a strange and startling sensation—reportedly the first manmade electric shock in history.

Musschenbroek repeated what Cunaeus had done, this time using a small glass bowl as his “Leyden jar.” “I would not take a second shock for the King of France,” he said.

Van Kleist in Pomerania produced the same effect. He lined the inside and outside of his Leyden jar with silver foil, charged the inner coat heavily, connected it with the outer foil by a wire which he held in his hand—and felt a violent shock run into his arm and chest.

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A Leyden jar could take any number of forms. Even a wine bottle would serve. The type used most frequently during the next few years was a glass tube, some two and a half feet long, and just big enough around so that a man might grasp it easily in his hand. The advantage of this size and shape was that it could most conveniently be electrified, which was then done by hand, by rubbing the glass with a cloth or buckskin. This simple device gave impetus to research on electricity throughout Europe. It also provided a new form of entertainment.

Performers went from town to town with their Leyden jars, giving spectators the thrill of receiving electric shocks, and extolling the marvels of “electrical fire.” Louis XV of France invited his guests to watch a novel spectacle arranged by his court philosopher, Abbé Jean-Antoine Nollet. The King’s Guard in full uniform lined up before the throne, holding hands. The first one was instructed to grasp the wire or chain connected to the Leyden jar. They all jumped convulsively into the air as an electric current passed through them.

In Italy some scientists tried to cure paralysis by electric shock, claiming moderate success. In May 1748, for instance, Jean-François Calgagnia, thirty-five years old, was given an electric shock from a simple cylinder-type Leyden jar. Since the age of twelve, his left arm had been so paralyzed he could not lift his hand to his head. After the first electrical treatment he at once raised his arm and touched his face. There is no record as to whether the cure was permanent.

After Franklin became aware of this phenomenon, he was agog to try experiments on his own. He wrote of his interest to a London friend, Peter Collinson, a Quaker merchant and member of the Royal Society. Collinson promptly sent him a glass tube, along with suggestions as to how it might be used for electrical experiments. This was all Franklin needed to get started.

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He was not trained in scientific matters as were many of his European contemporaries. He was unfamiliar with scientific jargon, and could only write about what he was doing in everyday language. But he had those qualities that are innate in any scientist, with or without a university degree—an inquiring mind, patience, and persistence.

His experiments, beginning with the winter of 1746, covered a wide range. He melted brass and steel needles by electricity, magnetized needles, fired dry gunpowder by an electric spark. He stripped the gilding from a book, and he electrified a small metallic crown above an engraving of the King of England—so that whoever touched the crown received a shock!

His home was soon so crowded with curious visitors trooping up and down the stairs, he could hardly get any work done. He solved the problem by having a glass blower make tubes similar to his, passing them out to friends so they could make their own experiments.

Several of the Junto members worked closely with him. At first they electrified the tube, as was still done in Europe, by vigorously rubbing one side of it with a piece of buckskin. One of the club members, a Silversmith named Philip Synge, devised a sort of grindstone, which revolved the tube as one turned a handle. To charge the tube with electricity, all that was needed was to hold the buckskin against the glass as it revolved, a vast saving in physical labor.

Another invention of Franklin and his associates was the first storage battery. For electrical plates they used eleven window glass panes about six by eight inches in size, covered with sheets of lead, and hung on silk cords by means of hooks of lead wire. They found it as easy to charge this “battery” with frictional electricity as to charge a single pane of glass.

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Among his disciples was an unemployed Baptist minister named Ebenezer Kinnersley. Franklin suggested he might both serve science and earn his living if he held electrical demonstrations. Kinnersley’s first announcement of a lecture, held in Newport, described “electrical fire” as having “an appearance like fishes swimming in the air,” claiming this fire would “live in water, a river not being sufficient to quench the smallest spark of it.” He promised his audience such wonders as “electrified money, which scarce anybody will take when offered ... a curious machine acting by means of electric fire, and playing a variety of tunes on eight musical bells ... the force of the electric spark, making a fair hole through a quire of paper....”

Kinnersley lectured in the colonies and the West Indies and was hugely successful. Neither he nor any of the other collaborators could rival Franklin’s own achievements.

Early in 1747, he gave the names of positive and negative (or plus and minus) to the two types of electricity, to replace the unwieldy terms, resinous and vitreous. Positive and negative electricity became part of the scientific vocabulary. He was the first to refer to the conductivity of certain substances. Electricity passed easily through metals and water; they were conductive. Glass and wood were nonconductive, unless they were wet. He also noted that pointed metal rods were wonderfully effective “in drawing off and throwing off the electrical fire.”

After he retired in 1748, he spent much more time on electricity. To Peter Collinson in London he wrote, “I never was before engaged in any study that so totally engrossed my attention and my time as this has lately done.” He kept Collinson informed in detail of his experiments, not because he thought he had the final word but in the hope that his experiments might possibly prove helpful to English scientists.

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It was to Collinson he described an electrical party to be held on the banks of the Schuylkill River in the spring of 1749: “A turkey is to be killed for our dinner by the electrical shock, and roasted by the electrical jack, before a fire kindled by the electrified bottle; when the healths of all the famous electricians in England, Holland, France, and Germany are to be drank in electrified bumpers, under the discharge of guns from an electrical battery.”

For Christmas dinner that year, he started to electrocute another turkey, but inadvertently gave himself the shock intended for the fowl: “The company present ... say that the flash was very great and the crack as loud as a pistol.... I neither saw the one nor heard the other.... I then felt ... a universal blow throughout my whole body from head to foot.... That part of my hand and fingers which held the chain was left white, as though the blood had been driven out, and remained so eight or ten minutes after, feeling like dead flesh; and I had a numbness in my arms and the back of my neck which continued till the next morning but wore off.”

He was apologetic rather than frightened by the near catastrophe, comparing himself to the Irishman “who, being about to steal powder, made a hole in the cask with a hot iron.”

This was soon after he had come to the conclusion that what he now called “electrical fluid” had much in common with lightning—that indeed they might be one and the same thing. He was not the first to propose this theory but no one before him had been able to suggest how it might be tested.

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Thunder and lightning had mystified humanity since the beginning of recorded history. The Greeks had held that thunderbolts were launched by the god Jupiter. (One Greek philosopher, Empedocles, thought that lightning was caused by the rays of the sun striking the clouds.) Hunters of primitive tribes prayed to the god of lightning, who was a killer, as they wished to be. Certain medicine men were said to be endowed with the gift of summoning lightning at will.

Since biblical days, lightning was assumed to be an act of heavenly vengeance, but no one could explain the paradox that it struck church steeples more frequently than other buildings. In medieval times, people believed that ringing church bells would keep lightning away, a belief that survived the death of countless unfortunate bell ringers.

About 1718, an English scientist, Jonathan Edwards, suggested that thunder and lightning might be produced by a “mighty fermentation, that is some way promoted by the cool moisture, and perhaps attraction of the clouds.” There had been very few other attempts to give a scientific explanation of the phenomenon, and even in Franklin’s time many preachers considered lightning a manifestation of the Divine Will.

“Electrical fluid” and lightning had in common, Franklin wrote in his notes on November 7, 1749, that they both gave light, had a crooked direction and swift motion, and were conducted by metals. Both melted metals and could destroy animals. Since they were similar in so many respects, would it not follow that lightning, like “electrical fluid” would be attracted by pointed rods? “Let the experiment be made.”

By May 1750, he was sure enough of his hypothesis that he elaborated to Peter Collinson the advantages to humanity of what later were called lightning rods:

I am of the opinion that houses, ships, and even towers and churches may be effectually secured from the strokes of lightning ... if, instead of the round balls of wood or metal which are commonly placed on tops of weathercocks, vanes, or masts, there should be a rod of iron eight or ten feet in length, sharpened gradually to a point like a needle ... the electric fire would, I think, be drawn out of a cloud silently, before it could come near enough to strike....

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Did he guess that he was on the verge of the most momentous discovery of the century—one which would assure his name a place among the immortals? It is fairly certain he was more interested in solving a perplexing problem than in immortality. Possibly he took it for granted that European scientists were already three steps ahead of him.

By July he had prepared a manuscript describing all his exciting experiments of the past two years, and including specific instructions for setting up a lightning rod on a tower or steeple, even to the necessary feature of a grounding wire. “Let the experiment be made,” he had said. He did not make it himself, not then. For one thing, he was waiting for a spire to be erected on the top of Christ Church, from which he wished to make his first try of drawing lightning from the skies. Also, in spite of his alleged retirement, his days were becoming increasingly filled with public duties.

He still had the Gazette and Poor Richard’s Almanack to publish and edit. Beginning in 1748, he served on the City Council. Since 1749 he was Grand Master of the Masons. In 1751 he was made an alderman and a member of the Pennsylvania Assembly, where previously he had served as clerk.

In 1750, an American Philosophical Society member, Dr. Thomas Bond, came to him for help in starting a hospital for the sick and the insane. Hitherto those who could not pay for medical care had no choice but the prison or the almshouse. The need was urgent but Dr. Bond had failed to arouse interest in his project.

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“Those whom I ask to subscribe,” he confided to Franklin, “often ask me whether I have consulted you and what you think of it. When I tell them I have not, they don’t subscribe.”

Franklin knew promotion methods as Dr. Bond did not, and began by calling a meeting of citizens. Under his impetus the list of subscribers grew, though not until May 1755 was the cornerstone of the Pennsylvania Hospital laid on Eighth Street between Spruce and Pine. Nearly thirty years later, when Dr. Benjamin Rush joined the staff, the “lunatics” at Pennsylvania Hospital received the first intelligent care available in America and, with few exceptions, in the world.

Franklin was also busy during this period in the formation of America’s first insurance company (stemming from a meeting of Philadelphia businessmen in 1752), and was taking the lead in organizing an expedition in search of a Northwest Passage, under Captain Charles Swaine, America’s first voyage of Arctic exploration.

In the category of pleasure were the infrequent periods he spent on his Burlington farm, where he raised corn, red clover, herd grass and oats, recording with scientific precision the effects of frost and the results obtained from different types of soil. He was one of the earliest Americans to think of agriculture as a science. He never could persuade his farmer neighbors to follow his example. They held that the ways of their forefathers were inevitably the best.

It may have been at his farm that he made his experiment on ants. Some ants had found their way into an earthen pot of molasses. He shook out all but one and hung the pot by a string to a nail in the ceiling. When the ant had dined to its satisfaction, it climbed up the string and down the wall to the floor. Half an hour later, he noted a swarm of ants retracing its course back to the pot—exactly as though their comrade had verbally informed them where to go for a good meal.

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There were few mysteries of nature on which at one time or another Franklin did not direct his attention. More often than not, he wrote his speculations in long and entertaining and gracefully phrased letters to his friends, men and women alike.

If he was not impatient to learn what Peter Collinson thought of his proposed lightning rods, it was simply that he had no time for impatience. The truth was that Collinson had found his paper fascinating and had even read it to the Royal Society. As the Society members remained skeptical and unimpressed, in 1751 he arranged for it to be printed in a pamphlet—“Experiments and Observations on Electricity, Made at Philadelphia, in America.” Dr. John Fothergill, a London physician, wrote the preface. The pamphlet was translated into French the next year, creating immediate excitement.

Three French scientists, the naturalist Count Georges Louis Buffon, Thomas François d’Alibard, and another named de Lor, resolved to carry out the experiment on drawing lightning from the skies, which Franklin had outlined.

It was d’Alibard who succeeded first. At Marly, outside of Paris, he set up a pointed iron rod forty feet long, not on a church steeple as Franklin had recommended, but simply on a square plank with legs made of three wine bottles to insulate it from the ground. During a thunderstorm, on May 10, 1752, a crash of thunder was followed by a crackling sound—and sparks flew out from the rod. Here then was absolute proof that Franklin was right. Lightning and electricity were identical.

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De Lor repeated the experiment in Paris eight days later. Louis XV, King of France, was so moved that he sent congratulations to the Royal Society, to be relayed to Messieurs Franklin and Peter Collinson. The first successful experiment in London was made by John Canton. Soon it was being repeated throughout Europe. The name of Benjamin Franklin was on everyone’s tongue.

No news of all this had yet been brought on the slow sailing ships when, in June 1752, Franklin decided not to wait for the completion of the Christ Church spire for his experiment. He had another scheme. Why not try to draw electricity from the skies with a kite?

“Make a small cross of two light strips of cedar, the arms so long as to reach to the four corners of a large thin silk handkerchief when extended; tie the corners of the handkerchief to the extremities of the cross.” Thus he later described the body of this world famous kite. Like ordinary kites, it had a tail, loop, and string. At the top of the vertical cedar strip, he fastened a sharp pointed wire about a foot long. At the end of the string he tied a silk ribbon. He fastened a small key at the juncture of silk and twine.

With this child’s plaything, he and his tall full-grown son, William, took off across the fields one threatening summer day. They let the wind raise the kite into the air and they waited. Even before it began raining, Franklin observed some loose threads from the hempen string standing erect. He pressed his knuckle to the key—and an electric spark shot out. There were more sparks when the thunderstorm began. After the string was wet, the “electric fire” was “copious.”

He must have grinned triumphantly at William, and perhaps said casually, “Well, Billy, we’ve done it.”

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There is no evidence that he realized his experiment might be dangerous, even deadly.

The first account of the “Electrical Kite” appeared five months later in the October 19, 1752, issue of the Gazette. Poor Richard’s Almanack for 1753 contained complete instructions on how to build a lightning rod. He had already put one up on his own chimney. It had small bells which chimed when clouds containing electricity passed by. The bells rang in his house for years.

News of his triumphs abroad were now flooding in. The praise of the French king, he wrote a friend, made him feel like the girl “who was observed to grow suddenly proud, and none could guess the reason, till it came to be known that she had got on a new pair of garters.” The Royal Society, making up for lost time, published an account of his kite in Transactions, their official paper, and in November 1753, gave him the Copley gold medal for “his curious experiments and observations on electricity.” They conservatively held off making him a member of the Society until May 29, 1756. At home, Harvard, Yale, and William and Mary College in turn gave him honorary degrees of master of arts.

While these and other tributes were being heaped on him, he was launching into a new profession—that of military expert and officer.

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