Q. _What prevents air being supplied, as fast as it is consumed by the fire?_ A. Leather and curtains round the doors; sand-bags at the threshhold and on the window-frames; and other contrivances to keep out the draught. Q. _Why is it needful for cold fresh air to be so constantly supplied?_ A. If water be taken with a pail out of a river, _other_ water will rush towards the hole, as soon as the pail is lifted out; and if air be taken from a room, (as it is, when some of it goes up the chimney) _other air_ will rush towards the void to fill it up. Q. _Why will it come down the chimney?_ A. Because if doors and windows are all made _air-tight_, it can get to the room in no _other_ way. Q. _What is the best REMEDY in such a case?_ A. The _speediest_ remedy is to open the door or window: but by far the _best_ remedy is to carry a small tube from the hearth into the external air. Q. _Why is that the BEST remedy?_ A. Because the fire will be plentifully supplied with air by the tube; the doors and windows may all remain air-tight; and we may enjoy a warm fireside, without the inconvenience of draughts and cold feet. Q. _Why is a CHIMNEY raised so high above the ROOF?_ A. If it were not so, it would smoke; as all funnels do which are too short. Q. _What is meant by the funnel, or flue of a chimney?_ A. That part of a chimney through which _the smoke passes_, is called the funnel, or flue. Q. _Why does a CHIMNEY SMOKE, if the funnel be very short?_ A. Because the _draught_ of a short flue _is too slack_ to carry the smoke up the chimney. Q. _Why is the DRAUGHT of a SHORT FLUE more SLACK that that of a long one?_ A. For many reasons. 1st--_The fire is always dull and sluggish_ if the chimney be too short. 2ndly--The smoke rolls _out_ of the chimney, before it has acquired its _full velocity_. 3rdly--The wind, rain, and air, have more influence over a _short_ funnel, than over a _long_ one. Q. _Why is the FIRE always DULL and sluggish if the CHIMNEY-FLUE be very SHORT?_ A. Because the draught is so bad: and as the rarefied air _passes up the chimney very tardily_, _fresh air_ flows as tardily _towards the fire_, to supply it with _oxygen_. Q. _On what does the INTENSITY of fire depend?_ A. The _intensity_ of fire is always in proportion to the _quantity of oxygen_ with which it is supplied. Q. _Why does not SMOKE acquire its full VELOCITY in a SHORT funnel?_ A. Because the _higher_ smoke ascends in a flue, (provided it be clear and hot) the _faster_ it goes; (as a stone falls faster and faster the lower it descends): if, therefore, a _funnel be very short_, the smoke never acquires its full velocity. Q. _Does the DRAUGHT of a chimney depend on the SPEED of the SMOKE through the flue?_ A. Yes. The more quickly _hot_ air flies _up the chimney_, the more quickly _cold_ air will rush _towards the fire_ to supply the place; and, therefore, the _longer the flue_, the _greater the draught_.