Some years after the publication of this essay, Franklin devised an improvement in the open chimney-place which tended to abate drafts and check the escape of heat up the chimney by contracting the chimney opening, bringing its breast down to within three feet of the hearth, and placing an iron frame just under this breast, with grooves on each side of the frame, in which an iron plate could be slid backwards and forwards at pleasure, for the purpose of cutting off the mouth of the chimney entirely from the chimney itself, when there was no fire on the hearth, or of leaving a space of not more than two inches for the escape of smoke between the further edge of the plate and the back of the chimney-mouth. This improved chimney-place was described by Franklin in letters to Alexander Dick and James Bowdoin. The letter to Bowdoin seems to leave little to be said on the subject of chimneys. It indicates that Franklin had subjected them to a scrutiny hardly less close than that which he had fixed upon the Leyden Jar. In connection with the currents and reverse currents, set up in them in summer by the relations of inequality, which the air in them sustains, at different hours of the day and night, to the outside temperature, he suggests that joints of meat might keep for a week or more during the hottest weather in chimney-openings, if well wrapt three or four fold in wet linen cloths, sprinkled once a day with water to prevent evaporation. Butter and milk in vessels and bottles covered with wet cloths might, he thought, be preserved in the same way. And he even thought, too, that the movements of air in chimneys might, with the aid of smoke-jack vanes, be applied to some mechanical purposes, where a small but pretty constant power only was needed. To appreciate how patiently and exhaustively Franklin was in the habit of pursuing every course of observation or reflection opened up by his scientific propensities, the whole of this letter, which had much more to say on the subject of chimneys than we have mentioned, should be read. At a later period of his life, Franklin describes to Turgot what he called his new stove. The novel feature of this consisted of an aerial syphon by which the smoke from the fireplace of the stove was first drawn upwards through the longer leg of the syphon, and then downwards through its shorter leg, and over burning coals, by which it was kindled into flame and consumed.