“To illustrate the fertilizing effect of plaster of Paris on lucerne, the following incident is related. Franklin, one of the chief glories of the United States of North America, aware of the great fertilizing power of plaster, wished to extend the agricultural use of this substance among his fellow-citizens; but they, clinging to old customs, would not listen to him. To convince them, Franklin spread plaster over a field of lucerne by the side of the most frequented road leading out of Philadelphia, but spread it in such a way as to form letters and words. The lucerne grew all over the field, but much taller, greener, and thicker where the plaster had been applied, so that the passers-by read in the field of lucerne these words traced in gigantic letters: ‘Plaster of Paris was applied here.’ The ingenious expedient was a great success and plaster was very soon adopted in agriculture.” “The doubters must have been convinced,” said Jules, “on seeing those big green letters rising above the rest of the lucerne. Did not Franklin do some other remarkable things? I remember the name; I have seen it several times in books.” “Yes,” replied his uncle, “Franklin became by his learning, one of the most remarkable men of his time. Among other things, we owe to him the invention of the lightning-conductor, that tall pointed iron rod erected on the roofs of buildings to protect them from the thunderbolt. It was he who first had the superb audacity to evoke the lightning from the midst of the thunder-clouds, to direct it according to his wishes, and to bring it to his feet that he might study its nature. One stormy day in 1752 he went out into the country near Philadelphia in company with his young son who carried a kite made out of a silk handkerchief tied at the four corners to glass rods. A pointed piece of metal terminated the apparatus. A long hemp cord, with a shorter cord of silk tied to the lower end, was fastened to the kite, which was then sent up toward a black thundercloud. At first nothing happened to confirm the previsions of the American sage, and he was beginning to despair of success when there came a shower of rain and with it a flash of lightning. The wet cord proved a better conductor than when dry. Without thinking of the danger he ran, and transported with joy at having brought within his reach that which causes thunder, Franklin put his finger near the cord and made little spurts of fire dart out, lighted brandy from these sparks out of the sky, and only brought his perilous experiment to an end when he had fully determined the origin and nature of thunder and lightning. This was the way he studied the mystery at close quarters, discovered its nature, and finally succeeded in protecting buildings by means of a pointed iron rod.