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 22 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. _Why does STRIKING a FLINT against a piece of STEEL produce a SPARK?_
A. The blow _condenses_ those parts of the flint and steel which strike _together_, and squeezes out their latent heat.
Q. _How does this development of HEAT produce a SPARK?_
A. A very small fragment (either of the steel or flint) _is knocked off red-hot_, and sets fire to the tinder on which it falls.
Q. _Why is it needful to keep BLOWING the TINDER with the breath?_
A. Because _blowing_ the tinder, drives the _oxygen of the air_ towards it.
Q. _Where does the OXYGEN of the air COME FROM, which is blown to the lighted tinder?_
A. The air itself is composed of two gases (_nitrogen and oxygen_) mixed together.
(Every 5 lbs. of common air contain 4 lbs. of nitrogen, and 1 lb. of oxygen.)
Q. _What is the good of BLOWING OXYGEN GAS to lighted tinder?_
A. Oxygen gas _supports combustion_; and lighted tinder is _quickened by the breath_, in the same way as a dull fire is revived by a _pair of bellows_.
Q. _Why do HORSES sometimes STRIKE FIRE with their FEET?_
A. When iron horse-shoes strike against the flint-stones of the road, _very small fragments_ (either of the shoe or stones) are _knocked off red-hot_, and look like sparks.
Q. _What makes these fragments RED-HOT?_
A. The percussion _condenses_ the part struck, _and squeezes out its latent heat_.
CHAPTER VIII.
2.--FRICTION.
3.--CONDENSATION.
Q. _What is meant by FRICTION?_
A. The act of _rubbing two things together_; as the Indians rub two pieces of _wood_ together to produce fire.
Q. _How do the Indians produce FIRE, by merely RUBBING TWO PIECES of dry WOOD TOGETHER?_
A. They take a piece of dry wood (sharpened to a point), which they rub quickly up and down a _flat piece_, till a _groove_ is made; and the _saw-dust_ (collected in this groove) soon _catches fire_.
Q. _Why does the saw-dust of the WOOD CATCH FIRE by RUBBING?_
A. The _latent heat_ of the wood is _developed by friction_; because the particles of the wood are _squeezed closer together_, and the heat pours out, as water from a sponge.
(The best woods for this purpose are _box-wood_ against _mulberry_, or _laurel_ against _poplar_ or _ivy_.)
Q. _Do not CARRIAGE WHEELS sometimes CATCH FIRE?_
A. Yes; if the wheels be _dry_,--or _fit too tightly_,--or _revolve very rapidly_,--they often catch fire.
Q. _Why do wheels catch fire in such cases?_
A. The _friction_ of the wheels against _the axle-tree_ is so great, that their _latent heat is disturbed_, and produces ignition.
Q. _What is the use of GREASING CART WHEELS?_
A. The grease _lessens the friction_; and (by diminishing the _friction_) the latent heat is less disturbed.
Q. _Why is the TOP of a MOUNTAIN COLDER than the VALLEY beneath, although it be two or three miles nearer to the sun?_
A. 1st--Because the air on a mountain is _less compressed_, than the air in a valley.
2ndly--It is _more rarefied_: and
3rdly--It is _less heated by reflection_.
Q. _Why is air COLDER on a mountain "because it is LESS COMPRESSED?"_
A. As the air in a _valley_ is more compressed (by the ma.s.s of air above) than that on the top of a _mountain_, therefore _more heat runs out_; just as more water runs from a sponge, the closer it is _squeezed together_.
Q. _Why is a mountain-top COLDER than a valley, "because the AIR there is MORE RAREFIED?"_
A. As the air is _more rarefied_, its heat is _diffused over a larger s.p.a.ce_ and is _less_ intense; just as a candle would _show less light_ in a _large_ room, than in a _small_ one.
