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 God "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 PRINCIPAL 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) God 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) God 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 quantity 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 passing 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?_