To improve Franklin’s thoughts about electricity, the physicists had to check thunderclouds are electrified. So three of them, Buffon, Dalibard and Delor carried out the experience and wait a thunderstorm. M. Dalibard chose for this purpose a large open area, situated at Marly-La-Ville, where he placed a pointed bar of iron, twenty-meter high. Silk ropes (g) and wine bottles (e) insulated a 13 meter iron rod (a) from ground, and covers (h) protected the ropes from rain. Then the 10th of May 1752, twenty minutes past two in the afternoon, a stormy cloud having passed over the place where the bar standing, people who were appointed to observe it, drew near and attracted from it sparks of fire, perceiving the same kind of reactions as in the common electrical experiments. The result of all the tests and observations were related in Dalibard’s mémoires and especially of the last test done at Marly-la-ville, is that the matter of thunder is incontestably the same as that of electricity. Franklin’s theory ceases to be a conjecture; it has become a reality. The sparks drawn at Marly-la-Ville proved, for the first time, that thunderclouds are electrified and that lightning is an electrical discharge.
Franklin's Lightning Rod 