A. When the two bodies are _separated by a non-conducting medium_: thus the sun _radiates_ heat towards the earth, because the _air comes between_ (which is a very bad conductor). Q. _On WHAT does RADIATION DEPEND?_ A. On the _roughness_ of the radiating surface: thus if metal be _scratched_, its radiating power is increased, because the _heat has more points to escape from_. Q. _Does a FIRE RADIATE heat?_ A. Yes; and because _burning fuel emits rays of heat_, therefore we _feel warm_ when we stand before a fire. Q. _Why does our FACE FEEL uncomfortably HOT, when we approach a FIRE?_ A. Because the fire radiates heat upon the face; which (not being _covered_) feels the effect immediately. Q. _Why does the fire catch the FACE more than the REST of the body?_ A. The _rest_ of the body is _covered with clothing_, which (being a _bad conductor_ of heat) prevents the same sudden and rapid transmission of heat to the skin. Q. _Do those substances which RADIATE heat, ABSORB heat also?_ A. Yes. Those substances which _radiate most_, also _absorb most heat_: and those which _radiate least_, also _absorb the least_ heat. Q. _Does any thing ELSE radiate heat, BESIDES the SUN and FIRE?_ A. Yes; _all_ things radiate heat in _some_ measure, but _not equally well_. Q. _What things RADIATE heat the NEXT BEST to the sun and fire?_ A. All _dull_ and _dark substances_ are _good radiators_ of heat; but all _light_ and _polished substances_ are _bad radiators_ of heat. Q. _Why does a POLISHED METAL TEA-POT make BETTER TEA than a black earthen one?_ A. As polished metal is a very _bad radiator_ of heat, it _keeps the water hot much longer_; and the hotter the water is, the better it "draws" the tea. Q. _Why will not a DULL BLACK TEA-POT make good tea?_ A. Because the heat of the water _flies off so quickly_ through the dull black surface of the tea-pot, that the _water is rapidly cooled_, and will not "draw" the tea. Q. _Do not pensioners, and most aged cottagers, prefer the little BLACK EARTHEN TEA-POT to the bright METAL one?_ A. Yes; because they _set it on the hob "to draw;"_ in which case, the little _black tea-pot_ will make the _best tea_. Q. _Why will a BLACK TEA-POT make better tea than a bright metal one, if it be set upon the HOB to DRAW?_ A. Because the black tea-pot will _absorb heat plentifully_ from the fire, and keep the water _boiling hot_: whereas, a bright _metal_ tea-pot (set upon the hob) would _throw off_ the heat by _reflection_. Q. _Then sometimes a BLACK EARTHEN tea-pot is the best, and sometimes a bright METAL one?_ A. Yes; when the tea-pot is _set on the hob "to draw,"_ the black _earth_ is the _best_, because it _absorbs heat_: but when the tea-pot is _not_ set on the hob, the bright _metal_ is the _best_, because it _radiates heat very slowly_, and therefore _keeps the water hot_. Q. _Why does a SAUCEPAN which has been USED, boil QUICKER than a NEW ONE?_