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<h2>CHAPTER VII.</h2> 118. Why does not a piece of wood which is turning at one end, feel hot at the other end? Because wood is a bad conductor of heat. 119. Why is wood a bad conductor of heat? Because the arrangement of the particles of which it is composed does not favour the transmission of caloric. 120. Why do some articles of clothing feel cold, and others warm? Because some are bad conductors of heat, and do not draw off much of the warmth of our bodies; while others are better conductors, and take up a larger portion of our warmth. [Pg 47] <hr class="bible-verse" /> "The fining pot is for silver, and the furnace for gold: but the Lord trieth the hearts."—Proverbs xvii. <hr class="bible-verse" /> 121. Which feels the warmer, the conductor or non-conductor? The non-conductor, as it does not readily absorb the warmth of our bodies. 122. What substances are the best conductors of heat? Gold, silver, copper, and most substances of close and hard formation, &c. 123. What substances are the worst conductors of heat? Fur, eider down, feathers, raw silk, wood, lamp-black, cotton, soot, charcoal, &c. 124. Why has the toasting-fork a wooden handle? Because wood is not so good a conductor as metal, therefore the wood prevents the heat from being transmitted by conduction to our hands. 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. 128. Of what use are kettle-holders? 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. [Pg 48] <hr class="bible-verse" /> "Wisdom is the principal thing; therefore get wisdom: and with all thy getting get understanding."—Proverbs iv. <hr class="bible-verse" /> 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. 135. If a person, sitting before a fire-place, without a fire, were to set one foot upon a rug, and the other upon the stone hearth, which would feel the colder? The foot on the stone, because stone is a good conductor, and would conduct the warmth of the foot away from it. [Pg 49] <hr class="bible-verse" /> "The earth is the Lord's, and the fulness thereof; the world, and they that dwell therein."—Psalm xxiv. <hr class="bible-verse" /> 136. What does the hearth-stone do with the heat that it receives? It delivers it to the surrounding air, and to any other bodies with which it may be in contact—and as it parts with heat, it takes up more from any body hotter than itself. 137. When there is no fire in a room, what is the relative temperature of the various things in the room? They are all of the same temperature. 138. If all the articles in the room are of the same temperature, why do some feel colder than others? Because they differ in their relative powers of conduction. Those that are the best conductors feel coldest, as they convey away the heat of the hand most rapidly. If you lay your hand upon the woollen table cover, or upon the sleeve of your coat or mantle, it will feel neither warm nor cold, under ordinary circumstances. But if you raise your hand from the table cover, or coat, and lay it on the marble mantel piece, the mantel-piece will feel cold. If now you return your hand from the mantel-piece to the table cover or coat, a sensation of warmth will become distinctly perceptible. This will afford a good conception of the relative powers of conduction of wool and marble. 139. How long does a substance feel cold or hot to the touch? Until it has brought the part touching it to the same temperature as itself. 140. When do substances feel neither hot nor cold? When they are of the same temperature as our bodies. 141. Why, under these circumstances, do they feel neither hot nor cold? Because they neither take heat from, nor supply it to, the body. 142. Which would feel the warmer, when the fire was lighted, the hearth-rug or the hearth-stone? The hearth-stone, because it is a good conductor, and would not only receive heat readily, but would part with it as freely (thereby [Pg 50] making its heat perceptible). But the hearth-rug, being a bad conductor, would part with its heat very slowly, and it would therefore be less perceptible. <hr class="bible-verse" /> "Fire and hail; snow and vapour; stormy wind fulfilling his word."—Psalm cxlviii. <hr class="bible-verse" /> 143. Would the hearth-stone feel hotter than the hearth-rug though both were of the same temperature? It would feel hotter than the hearth-rug, because it would part with its heat so rapidly that it would be the more perceptible. 144. But if the hearth-stone and the hearth-rug were both colder than the hand, which would feel the colder of the two? Then the hearth-stone would feel the colder, because, being a good conductor, it would take heat from the hand more freely than the hearth-rug, which is a bad conductor. 145. Why would the hearth-stone feel comparatively hotter in the one case, and colder in the other? Because, being a good conductor, it would conduct heat rapidly to the hand when hot, and take heat rapidly from the hand when cold. <hr class="chap" /> <div style="break-after:column;"></div>

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