A Guide To The Scientific Knowledge Of Things Familiar - novelonlinefull.com
You’re read light novel A Guide To The Scientific Knowledge Of Things Familiar Part 43 online at NovelOnlineFull.com. Please use the follow button to get notification about the latest chapter next time when you visit NovelOnlineFull.com. Use F11 button to read novel in full-screen(PC only). Drop by anytime you want to read free – fast – latest novel. It’s great if you could leave a comment, share your opinion about the new chapters, new novel with others on the internet. We’ll do our best to bring you the finest, latest novel everyday. Enjoy
Q. _What is meant by REFLECTING HEAT?_
A. To reflect heat, is _to throw it back in rays_ from the surface of the reflecting body, towards the place from whence it came.
Q. _What are the BEST REFLECTORS of heat?_
A. All _bright_ surfaces, and _light colours_.
Q. _Are GOOD ABSORBERS of heat GOOD REFLECTORS also?_
A. No; those things _which absorb heat best, reflect_ heat _worst_; and those _which reflect heat worst, absorb_ it _best_.
Q. _Why are those things which ABSORB HEAT unable to REFLECT it?_
A. Because if any thing _sucks in heat_ like a sponge, it cannot _throw it off_ from its surface; and if any thing _throws off heat_ from its surface, it cannot _drink it in_.
Q. _Why are REFLECTORS always made of LIGHT-COLOURED and highly POLISHED METAL?_
A. Because _light_ coloured and _highly polished metal_ makes the best of all reflectors.
Q. _Why do not PLATE-WARMERS BLISTER and scorch the WOOD behind?_
A. Because the bright tin front _throws the heat of the fire back again_, and will not allow it to penetrate to the wood behind.
Q. _If metal be such an excellent CONDUCTOR of heat, how can it REFLECT heat, or throw it off?_
A. Polished metal is a _conductor of heat_, only when _that heat is communicated by actual contact_; but whenever heat _falls upon bright metal in rays_, it is _reflected back again_, and the metal remains _quite cool_.
Q. _What is meant by "heat falling upon metal IN RAYS," and not "by contact"?_
A. If a piece of tin were thrust _into_ a fire, it would be _in actual contact with the fire_; but if it be _held before a fire_, the heat of the fire _falls upon it in rays_.
Q. _What is the use of the TIN SCREEN or REFLECTOR used in ROASTING?_
A. The tin reflector _throws the heat of the fire back upon the meat_; and, therefore, a.s.sists the _process of roasting_ and helps _to keep the kitchen cool_.
Q. _How does a tin REFLECTOR tend to keep the KITCHEN COOL?_
A. Because it _confines the heat to the hearth_, and prevents it from being dispersed throughout the kitchen.
Q. _Why does a LAMP GLa.s.s DIMINISH the SMOKE of a LAMP?_
A. As _gla.s.s is a reflector_, it reflects the heat of the lamp _back upon the flame_; in consequence of which, _less carbon escapes unconsumed_ (as smoke).
Q. _Why are SHOES HOTTER for being DUSTY?_
A. 1st--Because dust absorbs heat: and
2ndly--As it destroys the _blackness of our shoes_, it prevents them from _throwing off the heat of our feet in rays_.
Q. _Why can we not SEE into the ROAD or STREET, when a CANDLE is lighted in a room?_
A. _Gla.s.s is a reflector_; and, therefore, throws the rays of the candle _back into the room_, and thus prevents our seeing into the road or street.
Q. _Why can persons in the DARK STREET see into a ROOM (lighted by a candle or lamp)?_
A. The pupil of the eye _expands greatly_, when persons are in the dark; and, therefore, when any one in the dark street looks into a light room, _his dilated pupil_ sees every thing distinctly.
Q. _Why does it always FREEZE on the TOP of a MOUNTAIN?_
A. Air is heated _by the reflection of the earth_, and not by the rays of the sun; and, as there is no earth round a mountain-top _to reflect heat_, therefore, it remains intensely cold.
CHAPTER XVI.
4.--RADIATION.
Q. _What is meant by RADIATION?_
A. Radiation means _the emission of rays_: thus the sun radiates both light and heat; that is, it emits _rays of light and heat_ in all directions.
Q. _When is heat RADIATED from one body to another?_
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?_
