At an earlier period than that of the discovery of the balloon, his inquisitive spirit had led him to the study of marsh-gas and the pacifying effect of oil upon troubled waters. In 1764, he had reason to believe that a friend of his had succeeded in igniting the surface of a river in New Jersey, after stirring up the mud beneath it, but his scientific friends in England found it difficult to believe that he had not been imposed upon; and the Royal Society withheld from publication among its Transactions a paper on the experiment, written by Dr. Finley, the President of Princeton College, and read before it. Franklin twice tried it in England without success, and he prosecuted his investigation with such energy and persistency that he finally contracted an intermittent fever by bending over the stagnant water of a deep ditch, and inhaling its foul breath, or, as would now be said, by being bitten by a mosquito hovering about it. In 1757, when on one of the ships, bound on Lord Loudon's fool's errand to Louisburg, he observed that the water in the wake of two of them was remarkably smooth, while that in the wake of the others was ruffled by the wind, which was blowing freshly, and, when he spoke of the circumstance to his captain, the latter answered somewhat contemptuously, as if to a person ignorant of what everybody else knew, "The cooks have, I suppose, been just emptying their greasy water through the scuppers, which has greased the sides of those ships a little." The incident, and what he had read in Pliny about the practice among the seamen of Pliny's time of calming rough seas with oil, made him resolve to test the matter by experiment at the first opportunity. This intention was afterwards strengthened, when he was again at sea in 1762, by the "wonderful quietness" of oil, resting on the surface of an agitated bed of water in the glass lamp swinging in his cabin, and by the supposition of an old sea captain that the phenomenon was in keeping with the practice, pursued by the Bermudians, of putting oil on water, when they would strike fish. By the same captain, he was told that he had heard that fishermen at Lisbon were in the habit of emptying a bottle or two of oil on the sea, when the breakers on the bar at that port were running too high for their boats to cross it in safety. From another person, he learnt that, when divers in the Mediterranean needed more light for their business, they spewed out from their mouths now and then a small quantity of oil, which, rising to the surface, smoothed out its refracting waves. This additional information supplied his curiosity with still further fuel. It all ended in his dropping a little oil from a cruet on a large pond at Clapham. The fluid spread with surprising swiftness over the surface, on which it had fallen; but he found that he had made the mistake of dropping it on the leeward, instead of the windward, side of the pond. When this