A Guide To The Scientific Knowledge Of Things Familiar Part 39

Q. _Why is the TIN FOOT-WARMER covered with FLANNEL?_

A. 1st--To prevent the perspiration of the foot from taking off the _polish_ of the tin:

2ndly--Flannel is a _very bad conductor_; and, therefore, helps to keep the tin hot _longer_: and

3rdly--If the feet were _not protected_, the conducting surface of the tin _would feel painfully hot_.

Q. _What harm would it be if the POLISH of the tin were injured by the perspiration of our feet?_

A. _Polished_ tin throws off its heat _very slowly_; but dull, scratched, painted, or dirty tin, _throws off its heat very quickly_: if, therefore, the tin foot-warmer were to _lose its polish_, it would _get cold in a much shorter time_.

Q. _Why are FURNACES and stoves (where much HEAT is required) built of porous BRICK?_

A. As bricks are bad conductors, they _prevent the escape of heat_: and are, therefore, employed where great heat is required.

Q. _Why are FURNACE DOORS, &c. frequently COVERED with a paste of CLAY and SAND?_

A. Because this paste is a _very bad conductor of heat_; and, therefore, prevents the _escape of heat from the furnace_.

Q. _If a stove be placed in the MIDDLE of a room, should it be made of bricks or IRON?_

A. A stove in the _middle of a room_ should be made of _iron_; because iron is an _excellent conductor_, and rapidly communicates its heat to the air around.

Q. _Why does the Bible say, that G.o.d "giveth SNOW like WOOL?"_

A. As _snow is a very bad conductor of heat_, it protects vegetables and seeds from the frost and cold.

Q. _How does the non-conducting power of SNOW PROTECT VEGETABLES from the FROST and cold?_

A. As snow is a bad conductor, it prevents the _heat_ of the earth _from being drawn off_ by the cold air which rests upon it.

Q. _Why are WOOLLENS and FURS used in COLD weather for CLOTHING?_

A. Because they are _very bad conductors_ of heat; and, therefore, _prevent the warmth of the body from being drawn off_ by the cold air.

Q. _Do not woollens and furs actually IMPART heat to the body?_

A. No; they merely _prevent the heat of the body from escaping_.

Q. _Where would the heat ESCAPE to, if the body were NOT wrapped in wool or fur?_

A. The heat of the body would _fly off into the air_; for the cold air (coming into contact with our body) _would gradually draw away its heat_, till it was as cold as the air itself.

Q. _What then is the PRINc.i.p.aL USE of CLOTHING in winter-time?_

A. _To keep the body air-tight_; and prevent the _external air_ (or wind) from _coming into contact with it_, to absorb its heat.

Q. _Why are BEASTS COVERED with FUR, HAIR, or WOOL?_

A. Because fur, hair, and wool are very _slow conductors of heat_; and (as dumb animals cannot be clad like human beings) G.o.d has given them a _robe of hair_ or wool, to _keep them warm_.

Q. _Why are BIRDS covered with DOWN or FEATHERS?_

A. Because down and feathers are _very bad conductors of heat_; and (as birds cannot be clad like human beings) G.o.d has given them a _robe of feathers to keep them warm_.

Q. _Why are WOOL, FUR, HAIR, or FEATHERS such SLOW CONDUCTORS of heat?_

A. Because a _great quant.i.ty of air_ lurks entangled between their fibres; and _air is a very bad conductor of heat_.

Q. _If AIR be a BAD CONDUCTOR of heat, why should we not feel as warm WITHOUT clothing, as when we are wrapped in wool and fur?_

A. Because the air (which is cooler than our body) _is never at rest_; and, therefore, fresh particles (perpetually pa.s.sing over our body) _keep drawing off the heat little by little_.

Q. _Why does the ceaseless CHANGE of air tend to DECREASE the WARMTH of a naked body?_

A. Thus:--the air which cases the body _absorbs as much heat from it as it can, while it remains in contact_; it is then blown away, and makes room for a _fresh coat of air_, which does the _same_.

Q. _Does the AIR (which encases a naked body) become by contact as WARM as the BODY itself?_

A. It would do so, if it remained _motionless_; but as it remains only _a very short time_, it absorbs as much heat as it _can in the time_, and pa.s.ses on.

Q. _Why do we feel COLDER in WINDY WEATHER, than in a CALM day?_

A. Because (in windy weather) the particles of air _pa.s.s over us more rapidly_; and every _fresh_ particle takes from us _some_ portion of heat.

Q. _Show the wisdom of G.o.d in making the AIR a BAD CONDUCTOR._

A. If air were a _good conductor_ (like iron and stone) the heat would be drawn _so rapidly from our body_, that we must be _chilled to death_.