His command of language had seldom been put to better use than in explaining the rather subtle ideas and conceptions in the early development of electricity. Even now after the lapse of one hundred and fifty years we seem to gain a fresher understanding of that subject by reading his homely and beautiful explanations; and modern students would have an easier time if Franklin were still here to write their text-books. His subsequent letters and essays were many of them even more happily expressed than the famous letters on electricity. In old editions of his works all his writings on science were collected in one place, so that they could be read consecutively, which was rather better than the modern strictly chronological plan by which they are scattered throughout eight or ten large volumes. As we look over one of the old editions we feel almost compelled to begin original research at once,--it seems so easy and pretty. There are long investigations about water-spouts and whirlwinds,--whether a water-spout ever actually touches the surface of the sea, and whether its action is downward from the sky or upward from the water. He interviewed sea-captains and received letters from people in the West Indies to help him, and those who had once come within the circle of his fascination were never weary of giving aid. He investigated what he called the light in sea-water, now called phosphorescence. The cause of the saltness of the sea and the existence of masses of salt or salt-mines in the earth he explained by the theory that all the water of the world had once been salt, for sea-shells and the bones of fishes were found, he said, on high land; upheavals had isolated parts of the original water, which on evaporation had left the salt, and this being covered with earth, became a salt-mine. This explanation was given in a letter to his brother Peter, and is really a little essay on geology, which was then not known by that or any other name, but consisted merely of a few scattered observations. Many of his most interesting explanations of phenomena appear in letters to the young women with whom he was on such friendly terms. Indeed, it has been said that he was never at his best except when writing to women. People believe, he tells Miss Stevenson, that all rivers run into the sea, and he goes on to show in his most clever way that some rivers do not. The waters of the Delaware, for example, and the waters of the rivers that flow into Chesapeake Bay, probably never reach the ocean. The salt water backing up against them twice a day acts as a dam, and their fresh water is dissipated by evaporation. Only a few, like the Amazon and the Orinoco, are known to force their fresh water far out on the surface of the sea. In this same letter he describes the experiments he made to prove that dark colors absorb more of the sun’s rays, and are therefore warmer than white.