125. _Why has the coffee-pot a wooden handle?_
Because the metal of the coffee-pot would otherwise _conduct the heat to the hand_; but wood, _being a bad conductor_, prevents it.
126. _Why does hot water in a metal jug feel hotter than in an earthenware one?_
Because metal, being a good conductor, _readily delivers heat to the hand_; but _earthenware, being an indifferent conductor_, parts with the heat slowly.
127. _How can we ascertain that wood prevents the conduction of heat to the hand?_
By passing the top of the finger along the wooden handle of the coffee-pot, until it reaches the point where the wood meets the metal. The wooden handle will be found to be _cool_, but the metal will feel _very hot_.
Being made of _bad conductors_, such as wood, paper, or woollen cloth, they will not readily _conduct_ the heat from the kettle to the hand.
[Verse: "Wisdom is the principal thing; therefore get wisdom: and with all thy getting get understanding."--PROVERBS IV.]
129. _Will a kettle-holder, being a bad conductor, sometimes conduct heat to the hand?_
Yes. But so slowly that the hand will not _feel the inconvenience of too much heat_.
130. _Why does hot metal feel hotter than heated wool, though they may both be of the same degree of temperature?_
Because metal gives out heat _more rapidly than wool_, by which it is made _more perceptible to our feelings_.
131. _Which would become cold first--the metal or the wool?_
The _wool_, because, although the metal conducts heat more rapidly, to a substance in contact with it, it does not _radiate heat_ as well as a _black and rough substance_.
132. _Why do iron articles feel intensely cold in winter?_
Because iron is one of the best conductors, and draws off heat from the hand very rapidly.
133. _What is the cause of the sensation called cold?_
When we feel cold, heat is being _drawn off from our bodies_.
134. _What is the cause of the sensation called heat?_
When we feel hot, our bodies are _absorbing heat_ from external causes.
The condition here implied is that of health, and of ordinary circumstances. A person in a condition of fever, suffering from intense heat arising from a diseased state of the blood, could not be said to be _absorbing heat_. Nor could such a description apply to a person who, by a very rapid walk, has raised the temperature of his body considerably above its natural state, by the _internal combustion_ which has already been described. A person feeling hot in bed, from excessive clothes, feels hot from the _development of heat internally_, which is not _conducted away_ with sufficient rapidity to maintain the natural temperature of the body.