A Guide To The Scientific Knowledge Of Things Familiar Part 38

Q. _Why then does the IRON HANDLE seem so MUCH COLDER than the WOODEN PUMP?_

A. Merely because the _iron is a better conductor_; and, therefore, _draws off the heat from our hand_ much more rapidly than wood does.

Q. _Why does a STONE or marble HEARTH feel to the feet so much COLDER than a CARPET or hearth-rug?_

A. Because _stone and marble are good conductors_, but _woollen carpets and hearth-rugs_ are very _bad conductors_.

Q. _Why does the STONE HEARTH make our FEET COLD?_

A. As soon as the hearth-stone has absorbed a portion of heat from our foot, it instantly disposes of it, and _calls for a fresh supply_; till the hearth-stone has become of the _same temperature as the foot placed upon it_.

Q. _Do not the woollen CARPET and HEARTH-RUG, also, conduct heat from the human body?_

A. Yes; (but being very _bad conductors_) they convey _the heat away so slowly_, that it is scarcely perceptible.

Q. _Is the COLD HEARTH-STONE and WARM CARPET then of the SAME TEMPERATURE?_

A. Yes; everything in the room is _really of the same temperature_; but some feel colder than others _because they are better conductors_.

Q. _How LONG will the hearth-stone feel cold to the feet resting on it?_

A. Till the _feet and the hearth-stone are both of the same temperature_; and then the sensation of cold in the hearth-stone will go off.

Q. _Why would not the HEARTH-STONE feel COLD, when it is of the SAME temperature as our FEET?_

A. Because the heat would no longer _rush out of our feet into the hearth-stone_, in order to produce an equilibrium.

Q. _Why does the HEARTH-STONE (when the fire is lighted) feel so much HOTTER than the HEARTH-RUG?_

A. The hearth-stone is an _excellent conductor_; and, therefore, _parts with its heat more readily_ than the woollen hearth-rug; which (being a very _bad conductor_) parts with its heat reluctantly.

Q. _Why does PARTING with HEAT RAPIDLY make the HEARTH-STONE feel WARM?_

A. As the heat of the stone rushes _quickly into our foot_, it raises its temperature _so suddenly_, that we cannot _help perceiving the increase of heat_.

Q. _Why does the non-conducting power of the HEARTH-RUG prevent its feeling so HOT as it really is?_

A. Because it parts with its heat _so slowly and gradually_, that we scarcely _perceive its transmission_ into our feet.

Q. _When we plunge our HANDS into a basin of WATER, why does it produce a sensation of COLD?_

A. Though the water (in which we wash) _is really warmer_ than the air of our bed-room; yet because it is a _better conductor_, it _feels colder_.

Q. _Why does the CONDUCTING power of water make it feel COLDER than the air, though in reality it is WARMER?_

A. Because _it abstracts heat from our hands so rapidly_, that we feel its loss; but the air abstracts heat _so very slowly_, that its _gradual loss is hardly perceptible_.

Q. _Is water a GOOD CONDUCTOR of heat?_

A. No; _no liquid is a good conductor_ of heat; but yet water is a _much better conductor than air_.

Q. _Why is WATER a BETTER CONDUCTOR of heat than AIR?_

A. Because _it is less subtile_; and the conducting power of any substance depends upon _its solidity_, or the _closeness of its particles_.

Q. _How do you know that WATER is NOT a GOOD CONDUCTOR of heat?_

A. Because water may be made to _boil at its surface_, without imparting sufficient heat to _melt ice a quarter of an inch below the boiling surface_.

Q. _Why are NOT LIQUIDS GOOD CONDUCTORS of heat?_

A. Because the heat (which should be transmitted) _produces evaporation_, and _flies off in the vapour_.

Q. _Why does a POKER (resting on the fender) feel so much COLDER than the HEARTH-RUG, which is further off the fire?_

A. The poker (being an excellent conductor) _draws heat from the hand much more quickly than the rug_, which is a bad conductor: and, therefore, (though both are _equally warm_) the poker seems to be much colder.

Q. _Why are HOT BRICKS (wrapped in cloth) employed in cold weather to KEEP the FEET WARM?_

A. Bricks are _bad conductors_ of heat, and cloth or flannel _still worse_: therefore a hot brick (wrapped in flannel) will _retain its heat a very long time_.

Q. _Why is a TIN PAN (filled with HOT WATER) employed as a FOOT WARMER?_

A. Because _polished tin_ (being a bad radiator of heat) _keeps hot a very long time_; and warms the feet resting upon it.

Q. _What is meant by being a "bad RADIATOR of heat?"_

A. To radiate heat is to _throw off heat by rays_, as the sun; a polished tin pan does _not throw off the heat of boiling water_ from its surface, but _keeps it in_.