_Thirdly_, TO be soon and agreeably warmed, is not the only Advantage we have from this Invention; but we are better warmed, at less than one Third of the usual Expence, at a moderate Computation. When the Mercury in my Thermometer, that was placed without Doors, stood the last Winter at Four Degrees below the Freezing Point, a Peck of Coals (_i. e._ the 144th Part of a Chaldron,) was sufficient to warm the Room for the whole Day, from Eight in the Morning to Eleven at Night. During all that Time the Mercury within the Room stood from 60 to 64 Degrees; much the same Degree of Heat with that of the 25th Day of last _June_, 1752, at Two o’Clock in the Afternoon; and, when that Observation was made, the Weather was as warm as usual at that Time of the Year. BUT before I set up this Stove, which is one of the smallest, there was seldom spent, in the Room, less than a Bushel of Coals, and sometimes more, in one Day, according to the Degree of Cold; and then we were obliged to have a Skreen to keep off the cold Air from the Backs of those who sat near the Fire; and only that Part of the Room was warm which was nearest the Fire. THE Air that enters the Room, through the Iron Canal of the Air-Box, is both fresh and warm; and computing the Swiftness of its Motion with the Area of its Passage, it will appear, that Ten Barrels, or near 60 Cubic Feet of Air is hourly introduced from the external Air, if the Door of the Room be shut. THIS warm Air comes into the Room with such Rapidity from the hot Iron Canal, that it turns several Paper Wheels with great Velocity, which are placed near the Opening that lets it into the Room. But as soon as the Door of the Room is opened, all the Wheels stand still; which proves what has been said before, That much warm Air is wasted in opening the Door; because the warm, or rarified Air, rushes through the cold Air with great Force: And the cold Air that comes in at the Door, being an over-balance to the Air entering from the hot Iron Canal of the Stove, entirely stops it from coming into the Room while the Door is open. IN like manner, if the Door of the Room be shut, and the Register that is fixed in the Smoke-Passage be turned so near as almost to shut it up, which may be done when the Coals upon the Fire are burnt to a Coke, then the whole Heat of the Fire will be forced into the Room, the warm Air will be stopt from coming through the hot Canal, and the Paper Wheels will stand still, as they did when the Door of the Room was open. THIS may seem a little unaccountable, but, when considered, it is plain, that the warm Air from the hot Canal cannot come into the Room, which is already full of Air, and in a perfect State of Rest, because there is no Passage for it to go out at; the Register having closed up the Funnel, and the Doors and Windows of the Room being shut.