In Franklin's day, lightning destroyed homes, barns and livestock, not to mention human beings. To 18th-century Americans, though, it was not merely an occurrence in nature but a form of judgment sent down by a disapproving God. The only way to appease divine wrath -- and avoid lightning's destructive effects -- was to pray during thunderstorms or to ring specially "baptized" church bells whose sound might keep the lightning away.
After his kite experiment, Franklin realized that lightning was a form of electricity. He also discovered that electric current would surge through metal and follow its path downward to the ground. In the summer of 1752, he installed the world's first lightning rods at the Pennsylvania State House and the Pennsylvania Academy. In 1753, he used the pages of "Poor Richard's Almanack" to make the case for his invention, describing how a pointed iron rod situated atop a tall structure could draw lightning to it, making storms less dangerous. "Poor Richard's" sold 10,000 copies, earning Franklin instantaneous fame.
But not everyone embraced his claim. By inventing the lightning rod, he was playing God, at least in the view of some of his contemporaries. They saw God's handiwork in all aspects of life, from the divine-right monarchies that governed men to the storms that crashed overhead. Franklin's invention, according to Mr. Dray, raised questions "of reason and faith, liberty and tyranny, science and superstition." The French scientist and clergyman Jean Antoine Nollet was among the most vocal detractors. He contended that it was "as impious to ward off Heaven's lightnings as for a child to ward off the chastening rod of its father."
New Englanders, though, started to come around, especially as the authority of their early clergy began to wane in the mid-18th century. They became dubious of the notion that providence controlled nature in every detail. Some people, Mr. Dray notes, "favored the idea that, although God no longer gave daily attention to the world, he had at Creation pre-programmed natural catastrophes to occur throughout time as a way of reminding humanity of its frailty."
In 1755, humanity seemed frail indeed. A massive earthquake hit Boston, sending tremors from Nova Scotia to South Carolina. An even greater earthquake in Lisbon a few days later killed tens of thousands. A renewed debate erupted over the cause of such destruction. Thomas Prince, a pastor of Boston's South Church (who believed that he had saved Boston from a French attack in 1746 by calling on God for a sea storm), insisted that lightning rods played a part, sending electricity down into the ground, where it joined the large quantity already there and built up "subterranean tension." John Winthrop, a professor of science at Harvard, argued that a "kind of undulatory motion" in the Earth, beneath the surface, caused earthquakes and that lightning rods had nothing to do with it. John Adams even joined the fray, siding with Winthrop.
In the end, Prince won in the court of public opinion, though Winthrop's arguments had the virtue of being true. The use of lightning rods in Boston declined for many years thereafter. Luckily, a technological development in Europe -- the increased size of field artillery -- led to the acceptance of lightning rods on the Continent. Vaults under churches and other high buildings housed the gunpowder for such war machines. When lightning struck, the results were disastrous. But a lightning rod, it was discovered, kept nature's spark away. St. Mark's Basilica in Venice got one in 1766.
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Mr. Dray's book boasts a delightful secondary theme: the parallels between Franklin's invention and America's revolutionaries. Both were using reason to thwart what many perceived to be the natural order of things. Both were battling entrenched superstitions and dogmatic faith. Both were, in a sense, "playing God."