A. The _fuel is decomposed_ (by combustion) into its simple elements, carbon and hydrogen gas. (see p. 33) Q. _Why does not a FIRE BLAZE on a FROSTY NIGHT, so long as it does upon another night?_ A. The air (being very cold) _rushes to the fire so rapidly_, that the coals burn out _faster_, and the inflammable gas _is sooner consumed_. Q. _Why does a FIRE burn CLEAREST on a FROSTY night?_ A. Because the volatile gases are quickly consumed; and the solid carbon _plentifully supplied with air_, to make it burn bright and intensely. Q. _Why does a FIRE burn more intensely in WINTER than in SUMMER time?_ A. Because the air is _colder_ in winter, than in summer-time. Q. _How does the COLDNESS of the air increase the HEAT of a fire?_ A. For two reasons: 1st--Because cold air being more _condensed_ than hot air, contains a greater _body_: and 2ndly--Cold air _rushes more quickly to the fire_, and supplies more _oxygen_. Q. _Why does the SUN, shining on a FIRE, make it DULL, and often put it out?_ A. 1st--When the sun shines, the air is rarefied; and, therefore, _flows more slowly to the fire_. 2ndly--As the air is _rarefied_, even that which _reaches_ the fire, _affords less nourishment_. Q. _Why does the air flow to the fire more TARDILY for being RAREFIED?_ A. The greater the _contrast_ (between the _external air_, and that _which has been heated by the fire_) the more _rapid_ will be the current of air towards that fire. Q. _Why does rarefied air afford LESS NOURISHMENT to fire, than cold air?_ A. Because it is _spread out_, (like a piece of gold _beaten into leaf_); and as a square inch of gold _leaf_ will not contain so much gold as a square inch of _bullion_--so, a square inch of _rarefied_ air has less _body_, than a square inch of _cold air_. Q. _Why does a FIRE burn more fiercely in the OPEN AIR?_ A. 1st--Because the _air out-of-doors_ is more _dense_, than the air in-doors: and 2ndly--Because air is _more freely supplied_ to a fire out-of-doors. Q. _Why is the air out-of-doors more DENSE than that in-doors?_ A. Because the circulation is more free; and as soon as any portion has been _rarefied_, it instantly escapes, and is supplied by _colder currents_. Q. _Why does not a FIRE burn so freely in a THAW, as in a FROST?_ A. During a thaw, the air is filled with _vapour_; and, both _moves too slowly_, and is _too much diluted_ to nourish the fire. Q. _Why does a FIRE burn so fiercely in WINDY weather?_ A. In windy weather the _air is rapidly changed_, and affords plentiful nourishment to the fire. Q. _Why do a pair of BELLOWS get a fire up?_ A. A pair of bellows, (like the wind), _drives the air more rapidly to the fire_; and the plentiful supply of oxygen soon makes the fire burn intensely. Q. _Why is a CANDLE BLOWN OUT by the breath, and not made more intense, like a fire?_