Part 25 (1/2)
A. If the balloon be 3 square feet in size, it is _lighter_ (when inflated) than 3 square feet of _common air_, and therefore _floats through it_; as a cork (at the bottom of a tub of water) would rise to the surface.
Q. _Why does SMOKE RUSH UP a CHIMNEY?_
A. The heat of the fire _expands the air in the chimney_; and (being thus made _lighter_ than the air around), it _rises up the chimney_, and carries the smoke in its current.
Q. _Why has a LONG CHIMNEY a greater DRAUGHT than a short one?_
A. Because air rises faster and faster the _higher it ascends_ in a chimney flue; the same as a stone falls faster and faster the _nearer it approaches to the ground_.
Q. _Why will a LONG chimney SMOKE, unless the FIRE be pretty FIERCE?_
A. If the fire be not pretty fierce, its heat will not be sufficient to _rarefy all the air in the chimney_; and then the chimney will _smoke_.
Q. _Why will the chimney smoke, if the fire be not BIG enough to heat ALL the air in the CHIMNEY FLUE?_
A. Because the _cold air_ (condensed in the upper part of the flue), _will sink from its own weight_, and sweep the ascending smoke _back with it_ into the room.
Q. _What is the use of a COWL upon a chimney-pot?_
A. The cowl acts as a _screen against the wind_, to prevent it from blowing into the chimney.
Q. _What HARM would the WIND do, if it were to BLOW into a CHIMNEY?_
A. 1st--It would prevent the smoke from getting out: and
2ndly--The _cold air_ (introduced into the chimney by the wind) _would fall down the flue_, and drive the smoke with it _back into the room_.
Q. _Why does a SMOKE-JACK turn round in a chimney?_
A. The current of hot air up the chimney, striking against the _oblique vanes of the smoke-jack_, drives them round and round; in the same way as the sails of a _wind-mill_ are driven round by the _wind_.
Q. _Why are some things SOLID, others LIQUID, and others GASEOUS?_
A. As _heat_ enters any substance, _it drives its particles further asunder_; and a _solid_ (like _ice_) becomes a _liquid_; and a _liquid_ (like _water_) becomes a _gas_.
Q. _Why does WATER SIMMER before it boils?_
A. The particles of water _near the bottom of the kettle_ (being formed into _steam_ sooner than the rest) _shoot upwards_; but are _condensed_ again (as they rise) _by the colder water_, and produce what is called ”simmering.”
Q. _What is meant by SIMMERING?_