One of the discomforts of colonial times, when large open fireplaces were so common, was a smoky chimney. Franklin’s attention was drawn to this question about the time that he invented the Pennsylvania fireplaces, and he made an exhaustive study of the nature of smoke and heated air. He became very skilful in correcting defects in the chimneys of his friends’ houses, and while he was in England noblemen and distinguished people often sought his aid. It was not, however, until 1785, near the close of his life, that he put his knowledge in writing in a letter to Dr. Ingenhausz, physician to the Emperor of Austria. The letter was published and extensively circulated as the best summary of all that was known on this important question. It is as fresh and interesting to-day as when it was written, and well worth reading, because it explains so charmingly the philosophy of some phenomena of common occurrence which modern books of science are not at much pains to make clear. His enemies, of course, ridiculed him as a chimney doctor, and his friends have gone to the other extreme in implying that he was the only man in the world who understood the action of heat and smoke, and that, alone and unaided, he delivered mankind from a great destroyer of their domestic comfort. But his letter shows that most of his knowledge and remedies were drawn from the French and Germans. In this, as in many other similar services, he was merely an excellent collector of scattered material, which he summarized so well that it was more available than before. He was by no means the only person in the world who could doctor a chimney; but there were few, if any, who could describe in such beautiful language the way in which it was done. He invented a stove that would consume its own smoke, taking the principle from a Frenchman who had shown how the flame of a burning substance could be made to draw downward through the fuel, so that the smoke was burnt with the fuel. But the way in which this invention is usually described would lead one to suppose that it was entirely original with Franklin. He was much interested in agriculture, and was an earnest advocate of mineral manures, encouraged grape culture, and helped to introduce the basket willow and broom-corn into the United States. He at one time owned a farm of three hundred acres near Burlington, New Jersey, where he tried agricultural experiments. He dabbled in medicine, as has been shown, and also wasted time over that ancient delusion, phonetic spelling.