Eripuit coelo fulmen, sceptrumque tyrannis, it was said of Benjamin Franklin: "He snatched the lightning from the sky, and the sceptre from the hands of tyrants." This phrase refers to Franklin's political achievements, while the reference to lightning recalls his famous experiment with a kite which, tradition has it, took place 246 years ago today, June 15th, 1752.
It was a showery, none too pleasant day in Philadelphia, with every appearance of thunder in the air. Franklin at the time was convinced lightning flashes were electrical in origin, and launched his kite upon a silken thread, near the end of which he had attached a metal key.
In due course, a thunderstorm developed, and as the silken thread got wet he saw his hypothesis confirmed. Although we have no first-hand account of the proceedings, Franklin told his friend, Joseph Priestley, all about it. And he in turn has recorded the famous story for posterity:
"Preparing therefore a large silk handkerchief with two cross sticks of a proper length on which to extend it, he took the first opportunity of approaching a thunderstorm.
"The kite being raised, a considerable time elapsed before there was any appearance of its being electrified. At length, just as he was beginning to despair of the contrivance, he observed some loose threads of the hempen string to stand erect and to avoid one another, just as if they had been suspended on a common conductor.
"Struck with this promising appearance, he immediately presented his knuckle to the key. Let the reader judge the exquisite pleasure he must have felt when at that moment the discovery was complete: he perceived a very evident electric spark."
Franklin was lucky to survive this dangerous experiment, but survive he did, and was immediately aware of all its implications.
"May it now be of use to mankind," he wrote, "in preserving houses, churches, ships etc from lightning, by directing us to fix on the highest parts of these edifices upright rods of iron, and from the foot of these rods a wire down the outside of the building into the ground, or down the shrouds of a ship and down her side until it reaches the water?"
"Franklin rods", as they came to be called - the devices we know today as lightning conductors - caught on very quickly. Their use became widespread in the American colonies during the late 1750s, and their first successful performance is reputed to have been in 1760 when one saved the house of a Mr West of Philadelphia from potential damage by a direct hit by a stroke of lightning.