HEAT. 



Surrounded with Seconds. 



Air, (it cooled in) 576 



16 grs. of raw silk 1284 



Ravellingsoftaffety . 1169 



Sewing silk, cut 917 



Wool 1118 



Cotton 1046 



Fine lint 1032 



' Beaver's fur 1296 



Hare's fur 1315 



Eider-down 1305 



Charcoal 937 



Lampblack 1117 



Wood-ashe? 927 



The worst conductors, as hares' fur 

 and eider-down, involve a large quantity 

 of air among the parts of which they 

 consist, to which, it is believed, they 

 chiefly owe the power of resisting the 

 passage of heat. The same substance 

 is found to have ditferent conducting 

 powers, in proportion to the closeness 

 or openness of its texture , as will be 

 seen by reference to the experiments on 

 silk, the twisted silk having the greatest 

 conducting power. 



The substances which form the warm- 

 est articles of clothing are those which 

 have the longest nap, fur, or down, on 

 account of the air which is involved re- 

 sisting the escape of the natural warmth 

 of the body. The imperfect conducting 

 power of snow arises from the same 

 cause ; and is of the greatest utility in 

 preventing the surface of the earth from 

 being injuriously cooled in many parts of 

 the world. It is affirmed, that while the 

 temperature of the air in Siberia has been 

 70 below the freezing point, the surface 

 of the earth, protected by its covering of 

 snow, has seldom been older than 32. 

 Advantage is taken of the imperfect 

 conducting powers of bodies for the 

 purpose of confining heat : furnaces are 

 frequently surrounded by a thick coat- 

 ing of clay and sand for some purposes ; 

 the interposition of a layer of charcoal, 

 or of a stratum of air, is very effectual 

 in preventing the escape of caloric. 

 Double windows may be seen at Ken- 

 sington Palace, and in many houses in 

 and about London, upon the same prin- 

 ciples. The air inclosed between the two 

 windows opposes great resistance to the 

 escape of the heat which is produced 

 within the house in winter, 



Loose clothing is warmer than such 

 as fits close, on account of the quantity 

 of imperfectly conducting air confined 

 around the body, resisting the escape of 

 heat. The same substances that pre- 

 vent the escape of heat, will be equally 

 effectual in preventing its admission; 



and ice-houses are constructed upon 

 this principle. 



The very different sensations which 

 we experience on touching substances 

 of different kinds, as ivory, marble, 

 glass, wood, are occasioned by the dif- 

 ferences of conducting powers in these 

 bodies. A piece of wood, for example, 

 being touched in cold weather, does not 

 seem so cold by very much as a piece 

 of iron in the same place, although they 

 are exactly of the same temperature, as 

 may be proved by the application of a 

 thermometer to them. The iron feels 

 colder, because, being a good conductor 

 of caloric, the heat existing in the hand 

 over that of the iron, has a tendency to 

 enter into the iron, that an equality of 

 temperature may be produced between 

 them, and the rapid abstraction of 

 caloric occasions the sensation allu- 

 ded to ; but wood, being a slow con- 

 ductor, it does not take away heat from 

 the hand so rapidly, and therefore does 

 not feel so cold. For the same reason, 

 when the iron and the wood are at high 

 temperatures, the former seems the hot- 

 test, because it imparts heat most readily. 



Operators who have frequently to 

 touch substances hotter or colder than 

 is agreeable, find it very convenient to 

 wear gloves of worsted, that substance 

 being a very bad conductor of heat. 



Count Rumford illustrated, by nume- 

 rous experiments, the very imperfect 

 conducting power of fluids : indeed, he 

 supposed it proved by his experiments 

 that they are absolutely non-conductors 

 of caloric. This opinion has been suc- 

 cessfully controverted, and fluids are 

 now generally admitted to have a very 

 small degree of conducting power. 

 It has been proved that water may be 

 made to boil in the upper part of a tube, 

 without imparting much heat to the 

 lower portions : that water may be 

 brought to the boiling point within one 

 fourth of an inch of ice without produc- 

 ing immediate liquefaction ; and that ice 

 is melted eighty times slower, when it is 

 fixed at the bottom of a cylindrical vessel, 

 with warm water above it, than when 

 it floats upon the surface of warm water. 



Dr. Murray, who was the most suc- 

 cessful opponent of Count Rumford's 

 theory, selects the following as one of 

 the most unobjectionable of the Count's 

 experiments. Over a piece of ice, fro- 

 zen in the bottom of a cylindrical glass 

 jar, and having a small projection of ice 

 rising from the centre of it, he poured 

 olive oil, at 32, to the height of three in- 



