The reason why : $b a careful collection of many hundreds of reasons for things which, though generally believed, are imperfectly understood. A book of condensed scientific knowledge for the million — John Stuart Mill — John Shaqi
The reason why : $b a careful collection of many hundreds of reasons for things which, though generally believed, are imperfectly understood. A book of condensed scientific knowledge for the million
John Stuart Mill · en
139. _How long does a substance feel cold or hot to the touch?_
Until it has brought the part touching it to the same temperature as
itself.
140. _When do substances feel neither hot nor cold?_
When they are of the same temperature as our bodies.
141. _Why, under these circumstances, do they feel neither hot nor
cold?_
Because they neither take heat from, nor supply it to, the body.
142. _Which would feel the warmer, when the fire was lighted, the
hearth-rug or the hearth-stone?_
The hearth-stone, because it is a _good conductor_, and would not
only _receive heat_ readily, but would _part with it as freely_
(thereby making its heat _perceptible_). But the hearth-rug, _being
a bad conductor_, would part with its heat very slowly, and it would
therefore be _less perceptible_.
[Verse: "Fire and hail; snow and vapour; stormy wind fulfilling his
word."--PSALM CXLVIII.]
143. _Would the hearth-stone feel hotter than the hearth-rug though
both were of the same temperature?_
It would feel _hotter than the hearth-rug_, because it would part with
its heat so rapidly that it would be the _more perceptible_.
144. _But if the hearth-stone and the hearth-rug were both colder than
the hand, which would feel the colder of the two?_
Then the hearth-stone would feel the colder, because, _being a good
conductor_, it would _take heat_ from the hand more freely than the
hearth-rug, which is a _bad conductor_.
145. _Why would the hearth-stone feel comparatively hotter in the one
case, and colder in the other?_
Because, _being a good conductor_, it would conduct heat rapidly _to_
the hand when hot, and take heat rapidly _from_ the hand when cold.
CHAPTER VIII.
146. _Which are the better conductors of heat, fluids or solids?_
Generally speaking, _solids_, especially those of them that are dense
in their substance.
147. _Why are dense substances the best conductors of heat?_
Because the heat more readily travels from particle to particle until
it pervades the mass.
148. _Why are fluids bad conductors of heat?_
Because of the want of _density_ in their bodies; and because a portion
of the imbibed heat always passes off from fluids by _evaporation_.
[Verse: "He casteth forth his ice like morsels: who can stand before
his word,"--PSALM CXLVII.]
149. _Why are woollen fabrics bad conductors of heat?_
Because there is a considerable amount of _air_ occupying the spaces of
the texture.
150. _Is air a good or a bad conductor?_
Air is a _bad conductor_, and it chiefly transmits heat, as water does,
by _convection_.
151. _Is water a good or a bad conductor?_
Water is an indifferent conductor, but it is a _better conductor than
air_.
152. _Why, when we place our hands in water, which may be of the same
temperature as the air, does the water feel some degrees colder?_
Because water, _being a better conductor than air_, takes up the warmth
of the hand _more rapidly_.
153. _Why, when we take our hands out of water do they feel warmer?_