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1、Figure 7.3 Title page of Franklins book Experiments and Observations on Electricity, 1751. (Photo courtesy of the Smithsonian Institution Libraries, Smithsonian Institution.)was joined at the bottom end to a silk ribbon about three feet long to serve as an insulator, and whose other end Franklin wou
2、ld hold in his hand to control the kite. Franklin fastened a metal key to the twine where it joined the silk ribbon. In the summer of 1752, Franklin and his son flew the kite on a common in Philadelphia on a stormy day (Figure 7.4). They took advantage of a shed to shield themselves from the rain, a
3、nd to keep the silk ribbon dry. A thundercloud passed, but there were no signs of electricity. Somewhat later, the loose ends of the fibers of the kite string suddenly stood erect from the string. Franklin put his knuckle near the key and received a strong spark. He then charged a Leyden jar, and ca
4、used a spark from it to ignite a spirit flare. He had demonstrated to his satisfaction that lightning was an electrical phenomenon. Success! On October 1, 1752, Franklin described the results of his experiment in a letter to Collinson.Figure 7.4 Franklin and his son conduct- ing a kite experiment to
5、 attract lightning. (Photo courtesy of the Bumdy Library, Dibner Institute for the History of Science and Technology.)Having shown that lightning was an electric discharge. Franklin pursued his earlier speculation that a lightning rod could perform the functions of discharging an approaching cloud,
6、and could also conduct a lightning flash harmlessly to moist earth. Protecting against its devastation by using lightning rods came slowly over the next several years. Father Procopius Divisch, a clergyman in Moravia, installed the first primitive lightning rod in 1754. In 1760 Franklin erected one
7、on a building in Philadelphia; William Watson erected the first lightning rod in England in 1762. By 1782 there were about 400 rods in Philadelphia. Franklins reputation as an experimenter with electricity grew rapidly. In November 1753, after his sentry-box and kite experiments, the Royal Society p
8、resented him the Sir Godfrey Copley Medal, their highest award. In May 1756 he was elected a Fellow of the Royal Society. The new technology, however, faced serious opposition, as do many new ideas. Many people thought that lightning and thunder were tokens of divine wrath, and considered it impious
9、 to interfere with their powers of destruction. The common sense reply: “It is as much our duty to secure ourselves against the effects of lightning as against those of rain, snow, and wind, by the means God has put into our hands“ (attributed to John Winthrop, the first Professor of Physics at Harv
10、ard College). Political pressure was also exerted against the acceptance of pointed rods. Many people in England believed that the upper ends of rods should be tipped with a sphere instead of a point. A scientist close to George III persuaded him that a sphere should be used on a military project. G
11、eorge III concurred, and for many years English lightning rods bore spheres on their upper ends. Franklin, too, lived in turbulent times, and through three wars: the Indian battles in western Pennsylvania (1744-1748); the French and Indian War (1755-1763), which decided whether France or England was
12、 to rule the colonies west of those on the Atlantic coast; and the Revolutionary War (1775-1783), leading to the beginnings of the United States.Franklin played an important part in domestic and international affairs throughout his life. The list of some of his important early offices includes Publi
13、c Printer for Pennsylvania (1730), Clerk of the Pennsylvania Assembly (1736), Postmaster at Philadelphia (1737), Member of the City Council of Philadelphia (1748), and Member of the Assembly for Pennsylvania (1750). Franklin made his second trip to England in 1759, during the French and Indian War,
14、to discuss the taxation of Pennsylvania and the Penn family. His next voyage abroad was in 1764, again representing Pennsylvania. Franklin was a moderate politically and worked hard for a peaceful resolution of the differences between the American colonies and the British. The Stamp Act and later To
15、wnshends Acts, however, made it almost impossible to be a loyal British subject and to represent the colonies at the same time. He returned to America in 1774, after short visits in Ireland, Scotland, France, and Germany. The Revolutionary War began in April 1775. Franklin worked with John Adams and
16、 Jefferson, the principal author, in writing the Declaration of Independence, which was proclaimed July 4, 1776. Shortly afterwards, the Continental Congress sent Franklin to France to enlist the French governments help in the colonies struggle to gain independence from England. Franklin was well known in France because of his scientific accomplishments, and was well received. French help was generous, but the war lasted several years l
