72 ANNUAL OF SCIENTIFIC DISCOVERY. 



them, that is to say, in the large volume which fills the space left over a com- 

 mon fire. The whole of the air so contaminated, and which may be in volume 

 30, 50, or 100 times greater than that of the true smoke, is then all called 

 smoke, and must ah 1 be allowed to ascend away from the room. It is evi- 

 dent, then, that if a hood or cover be placed over a fire, so as to prevent the 

 diffusion of the true smoke or the entrance of pure air from around to mix 

 with it, except just what is necessary to burn the inflammable gases which 

 rise with the true smoke, there would be a great economy. This has been 

 done in the new fire-place, with a saving of from one third to one half of the 

 fuel required to maintain a desired temperature. 



The stalk of the hood passes closely through a plate or other stopping 

 through the bottom of the chimney, so that no air shall enter the chimney 

 but through the hood ; and there is a throttle-valve or damper in the hood- 

 stalk, giving perfect control over the current of air that passes through. No 

 part of the apparatus is more important than this valve or damper, and its 

 handle or index must be very conspicuous, and have degrees of opening marked 

 on its plate as clearly as the points are marked on a compass card. "When 

 the valve is quite open, the chimney acts to quicken the combustion, like 

 that of a blast furnace, or like a forge-bellows, but, by partially closing the 

 valve, the current may be diminished until only the most tranquil action re- 

 mains. The valve should not be open in general more than just enough to 

 let all the burned air or thin smoke, which is scarcely visible, pass through. 

 "When the valve is once adjusted to the usual strength of chimney action, it 

 requires little change afterward. In many cases, it is desirable to be able to 

 command and modify, by a movable plate, the size of the front opening of 

 the hood or fire-place, as well as the opening of the chimney-throat. By the 

 proper adjustment of the two, the desirable brightness of the front of the fire 

 may be maintained. The chimney-flue above the upper opening of the hood 

 should have its sides made slanting, so as not to harbor dust or any soot 

 which, from any careless use of the fire, might be produced. The size of the 

 chimney-flue is not important. Other great evils of the present open fires are 

 that there are great irregularities and deficiencies in their heating and venti- 

 lating actions, which bear so powerfully on the public health. The hood and 

 its damper, by influencing these, may appear, perhaps, of more importance 

 than as saving the fuel. This arrangement, by allowing so small a quantity 

 of air to pass through in comparison with what rises in an open ordinary 

 chimney, lessens in the same degree the cold draught of ah* toward the fire 

 from doors and windows, and which are common causes to the inmates of 

 winter inflammation and other diseases ; and for the same reason, the heat 

 once radiated from the fire toward the walls of the room, not being again 

 quickly absorbed and carried away by such currents of cold air as are referred 

 to, remain in the room, and soon renders the temperature of the whole more 

 equable and safe. Still more completely to prevent cold draughts approach- 

 ing from behind persons sitting around the fire, the fresh air from the room is 

 conveniently admitted, chiefly by a channel which leads directly from the ex- 

 ternal ah* under the floor to the hearth, and there allows the air to spread 

 from under the fender. The fender, exposed to the fire near it, becomes hot 5 



