166 Heat and Organization. 



large bronze statue. " The iron folding-doors of the small 

 room or oven were opened. Captain Kater and myself entered. 

 The farther corner of the room, which was paved with square 

 stones, was visibly of a dull red heat. The thermometer 

 marked, if I recollect rightly, 265°. The pulse was quickened, 

 and I ought to have counted but did not count the number of 

 respirations per minute. Perspiration commenced immediately, 

 and was very copious. We remained, I believe, about five or 

 six minutes without any very great discomfort, and I ex- 

 perienced no subsequent inconvenience from the result of the 

 experiment."* 



Bodies may receive and part with heat in two distinct 

 ways — by conduction and by radiation. If we hold our hands 

 near the fire, or a hot iron, we are warmed by the heat that is 

 radiated. If we touch a glowing coal or a hot iron, we are 

 warmed or burnt by the heat that is conducted from the hot 

 body to ourselves. Radiation takes place at any distance. Con- 

 duction requires contact. The nearer we are to the radiating 

 body the more heat we receive, and if we recede from it, we 

 lose the heating effect as the square of the distance is 

 increased. 



Water is a bad conductor of heat, the ordinary metals 

 conduct it well, hair and fur conduct it badly, mica and 

 such bodies still worse. A couple of inches of iron can be 

 heated through very quickly, but a couple of inches of talc 

 or mica keeps out the heat for a long time, and a box of metal 

 with sides sufficiently thick to resist fusion, may be made 

 fireproof by lining it with a couple of inches of a very badly 

 conducting substance like those we have named. 



Bodies differ in radiating power as well as in conducting 

 power. A bright metal teapot radiates little and keeps 

 warm, while a black earthenware one radiates much, and 

 gets cool in the same time. 



Heat may be reflected like light, and good reflecting sur- 

 faces will keep heat out, while good absorbing ones will take 

 it in. 



The escape of heat by radiation from the earth's surface, 

 varies according to soil, climate, and state of the weather. In 

 clear, dry air it goes on with rapidity, so that frost at night 

 follows a sweltering heat by day, and no animal or vegetable 

 can live in such countries, unless fitted to bear sudden and 

 violent extremes. Moisture, or vapour in the air arrests the 

 dispersion of heat by radiation, and hence climates that are 

 temperate are never excessively dry. Even perfumes exert 

 powerful effects. Most minute are the quantities of matter 

 given off in the scent of flowers. " No chemist," as Prof. 

 * Passages from the Life of a Philosopher, p. 213. 



