and along the ceiling. The circular vane or ventilator sometimes fixed in windows admits cold air in a similar manner, when the supply for the room and fire would be otherwise deficient. The opening or breadth and height of the fire-place, though we may fancy it leads to the diffusion of more heat into the room, is really a cause of loss of fuel, and of smoke. The size of the fire-place opening is often considered in relation to the size of the room, without regard to the principles on which a fire is maintained in a grate; a course about as rational (it has been well observed) as to proportion the step in a staircase to the height of the story, instead of to the convenience of our legs in mounting them. As the chimneys of different rooms are unavoidably of different heights, and as the force of the draught is in proportion to the height of chimney filled with warmed and rarefied air, it is found that the opening for a tall chimney may be larger than for a lower one. If the opening be unnecessarily large, there is room not only for the entrance of fresh air, but also for the exit of smoke driven down by an opposing current from the chimney itself; and the air, too, ascends into the chimney in too cold a state, because the largeness of the opening enables it to enter without passing very close to the fire. The principal evil attending the use of a fire-place having too small an opening, is that the fuel is burned away with unnecessary rapidity. When the opening is found by experience to be so large as to lead to the descent of smoke into the room, the easiest remedy is to place moveable boards or sheets of tin or iron, so as to lower and narrow it gradually. The effect of which, by excluding a part of the colder air from the chimney, is to produce a quicker action, so that the fire begins to roar as if blown by a bellows. “This means is often used to blow the fire instead of bellows, or to cure a smoky chimney, by increasing the draught. What is called a _register stove_ is a kindred contrivance. It has a flap placed in the throat of the chimney, which serves to widen or contract the passage at pleasure. Because the flap is generally opened only enough to allow that air to pass which rises directly from the fire, the chimney receives only very hot air, and therefore acts well. The register stove often cures smoky chimneys; and by preventing the too ready escape of the moderately warmed air of the room, of which so much is wasted by a common fire-place, it also saves fuel.” There does not appear to have been any attempt to determine by experiment the proper opening of the fire-place for a given height of chimney; and, indeed, there are so many disturbing causes, that it would be scarcely possible to determine this with precision. Dr. Franklin, however, proposed to make the fire-place openings in the lower rooms about thirty inches square and eighteen inches deep; those in the upper, eighteen inches square, and