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 41 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
A. As the earth is a _bad conductor_, the burning rays of the sun can penetrate only a few inches below the surface; in consequence of which, the _springs of water are not affected_.
Q. _Why is it COOL under a SHADY tree in a hot summer's day?_
A. 1st--Because the overhanging foliage _screens off the rays of the sun_:
2ndly--As the rays of the sun are warded off, _the air_ (beneath the tree) _is not heated by the reflection of the earth_: and
3rdly--The leaves of trees, being _non-conductors_, allow no heat to penetrate through them.
Q. _Why do the LAPLANDERS wear SKINS, with the FUR INWARDS?_
A. The _dry skin_ prevents the _wind from penetrating to their body_; and as the _fur_ contains a _quant.i.ty of air_ between its hairs (which soon _becomes heated by the body_) the Laplander is clad in _a case of hot air, impervious to the cold and wind_.
Q. _Why does a LINEN SHIRT feel COLDER than a COTTON ONE?_
A. _Linen is a much better conductor_ than cotton; and, therefore, (as soon as it touches the body) _it more rapidly draws away the heat_, and produces a sensation of cold.
Q. _Why is the FACE COOLED by wiping the temples with a fine CAMBRIC HANDKERCHIEF?_
A. The fine fibres of the cambric have a _strong capillary attraction for moisture_; and are _excellent conductors of heat_: thus the moisture and heat are _both abstracted from the face_, and a sensation of coolness is produced.
"Capillary attraction," i. e. _the attraction of a thread or hair_. The wick of a candle is wet with grease, because the melted tallow runs up the cotton from capillary attraction.
Q. _Why would not a COTTON handkerchief do as well?_
A. The coa.r.s.e fibres of cotton have much less capillary attraction, and are _nothing like such good conductors_ as linen: and, therefore, wiping the face with a _cotton handkerchief_, increases the sensation of warmth.
CHAPTER XIV.
2.--ABSORPTION OF HEAT.
Q. _What is the difference between CONDUCTING heat, and ABSORBING heat?_
A. To _conduct_ heat, is to _transmit it from one body to another_ through a conducting medium: to _absorb_ heat, is to _suck it up_, as a sponge sucks up water.
Q. _Give me an example._
A. _Black cloth absorbs_, but does not _conduct heat_: thus, if black cloth be laid in the sun, _it will absorb the rays_ very rapidly; but if _one end of the black cloth_ be made hot, it would not _conduct the heat_ to the _other_ end.
Q. _Are good CONDUCTORS of heat, good ABSORBERS also?_
A. No; every _good conductor of heat_ is a _bad absorber of it_; and _no good absorber of heat_ can be a _good conductor_ also.
Q. _Is IRON a good ABSORBER of heat?_
A. No; _iron is a good conductor_, but a very _bad absorber_ of heat.
Q. _Why do the FENDER and FIRE-IRONS (which lie upon it) remain COLD, although they are before a good fire?_
A. Because the metal fender and fire-irons have very _little capacity for absorbing heat_; although they are soon made hot (by conduction), when placed in _contact_ with the hot fire or stove.
Q. _Why does a KETTLE boil faster, when the bottom and back are COVERED with SOOT?_
A. The _black soot absorbs heat_ very quickly from the fire, and the metal _conducts it to the water_.
Q. _Why will not a NEW KETTLE boil so fast as an OLD one?_
A. Because the _bottom and sides_ of a new kettle are _clean and bright_; but in an _old_ kettle _are covered with soot_.
Q. _Why would the KETTLE be SLOWER BOILING, if the BOTTOM and BACK were CLEAN and bright?_
A. _Bright_ metal does _not absorb heat_, but _reflect it_ (i. e. throw the heat _back_ again); and as the heat is _thrown off from the surface of bright metal_, therefore, a new kettle is longer boiling.
Q. _Why do we wear WHITE LINEN and a BLACK outer DRESS, if we want to be warm?_
A. The _black outer dress_ quickly _absorbs heat from the sun_, and conveys it to the body; and the _white linen_ (being a _bad_ absorbent) abstracts no heat from the warm body.
Q. _Why do persons WEAR WHITE dresses in SUMMER time?_
A. White _throws off the heat of the sun by reflection_, and is, therefore, a very bad absorbent of heat; in consequence of which, it never becomes _so hot from the scorching sun_ as dark colours do.
Q. _Why do NOT persons WEAR WHITE dresses in WINTER time?_
A. _White will not absorb heat_, like black and other dark colours; and, therefore, _white_ dresses are _not so warm as dark ones_.
Q. _What COLOURS are WARMEST for dresses?_
A. For _outside_ garments _black is the warmest_, and then such colours as _approach nearest to black_ (as dark blue and green). _White is the coldest colour_ for external clothing.
