Q. In what way does caloric so expand bodies? A. The caloric is supposed to be so introduced as to be wedge-like in its effect among the particles of bodies: by this they are removed to a greater distance from each other, they occupy more space, become larger; if the expansion is unequal, they crack or split. Q. As caloric is so widely diffused, does it exist every where in the same state? A. Caloric is said to exist in two states. Q. What are they? A. A state of liberty, and a state of combination. A. Caloric in combination, or, as it is sometimes termed, latent heat, does not immediately affect the sense of feeling : it is not indicated by the thermometer; it exists as a constituent part of a body, but it may be brought to the state of sensible heat:—while caloric at liberty is the heat that is felt; and in degree is indicated by the thermometer. This is generally denominated free caloric. Q. What is the operation, and what are the advantages, of free caloric? A. The particles thereof are supposed to pass continually in every possible direction, and by equal diffusion tend to equalize the temperature of surrounding bodies. Q. Make this plain by some example. A. If a heated body be placed in contact with one that is cold, the former parts with a portion of its caloric to the latter, until they both become of an equal, but, compared with what they were before, an intermediate temperature. If a cold body be brought into a warm room, it will take a portion of the caloric which the room contains. This may be felt, if first hot iron be brought into a room, and afterwards ice. What we term fire would be an example of this, if combustion did not continue; the room and the cinders would become equal in temperature. Q. How does caloric thus tend to equalize the temperature of surrounding objects? A. By its radiation from all bodies. A. Yes; this is taken to be the fact. Q. How may I know this? A. Place the hand on a piece of marble; it feels cold, and takes a portion of caloric from it. But place a piece of ice on the marble, and the part in immediate contact dissolves, by receiving more caloric from the marble than it has given. Q. Do all surfaces radiate caloric in an equal degree? A. They do not: black radiates much more than white, and glass more than a polished metallic surface. Q. By what means can this be ascertained? A. Take a cubical tin canister; blacken one of its sides, cover the second with white paper, on the third place a piece of glass, and leave the fourth surface unaltered. Fill the canister with boiling water; and it may be found by mirrors and a thermometer, that the black side radiates the most heat, and the paper, glass, and tin surface, less in suc cession. Q. But generally do different surfaces thus radiate caloric? A. It is supposed that they do. Q. How then can they continue all to radiate caloric? Will not the one radiate the whole before the other? A. No; it is found that the bodies which radiate caloric in the greatest degree, absorb it also in the same proportion. Q. Can this be made apparent by any example? A. Yes: take pieces of cloth of the same dimensions, as black, red, &c., to white; place these differently-coloured pieces on snow, when the sun shines; it will be found that the black piece will soon begin to sink therein, the red next, but the white will remain on the surface. The former absorbed heat, and the snow dissolved; the latter reflected heat, and the snow continued unaltered. Q. What is the difference between the radiation and the reflection of caloric ? A. The caloric radiated, is that which properly belongs to the body: the caloric reflected, is that which falls on the surface from other bodies. Q. The tin surface radiated the least heat; but if I touch Q. In what way does caloric so expand bodies? A. The caloric is supposed to be so introduced as to be wedge-like in its effect among the particles of bodies: by this they are removed to a greater distance from each other, they occupy more space, become larger; if the expansion is unequal, they crack or split. Q. As caloric is so widely diffused, does it exist every where in the same state? A. Caloric is said to exist in two states. Q. What are they? A. A state of liberty, and a state of combination. A. Caloric in combination, or, as it is sometimes termed, latent heat, does not immediately affect the sense of feeling : it is not indicated by the thermometer; it exists as a constituent part of a body, but it may be brought to the state of sensible heat:—while caloric at liberty is the heat that is felt; and in degree is indicated by the thermometer. This is generally denominated free caloric. Q. What is the operation, and what are the advantages, of free caloric ? A. The particles thereof are supposed to pass continually in every possible direction, and by equal diffusion tend to equalize the temperature of surrounding bodies. Q. Make this plain by some example. A. If a heated body be placed in contact with one that is cold, the former parts with a portion of its caloric to the latter, until they both become of an equal, but, compared with what they were before, an intermediate temperature. If a cold body be brought into a warm room, it will take a portion of the caloric which the room contains. This may be felt, if first hot iron be brought into a room, and afterwards ice. What we term fire would be an example of this, if combustion did not continue; the room and the cinders would become equal in temperature. Q. How does caloric thus tend to equalize the temperature of surrounding objects? A. By its radiation from all bodies. A. Yes; this is taken to be the fact. Q. How may I know this? A. Place the hand on a piece of marble; it feels cold, and takes a portion of caloric from it. But place a piece of ice on the marble, and the part in immediate contact dissolves, by receiving more caloric from the marble than it has given. Q. Do all surfaces radiate caloric in an equal degree? A. They do not: black radiates much more than white, and glass more than a polished metallic surface. Q. By what means can this be ascertained? A. Take a cubical tin canister; blacken one of its sides, cover the second with white paper, on the third place a piece of glass, and leave the fourth surface unaltered. Fill the canister with boiling water; and it may be found by mirrors and a thermometer, that the black side radiates the most heat, and the paper, glass, and tin surface, less in succession. Q. But generally do different surfaces thus radiate caloric? A. It is supposed that they do. Q. How then can they continue all to radiate caloric? Will not the one radiate the whole before the other? A. No; it is found that the bodies which radiate caloric in the greatest degree, absorb it also in the same proportion. Q. Can this be made apparent by any example? A. Yes: take pieces of cloth of the same dimensions, as black, red, &c., to white; place these differently-coloured pieces on snow, when the sun shines; it will be found that the black piece will soon begin to sink therein, the red next, but the white will remain on the surface. The former absorbed heat, and the snow dissolved; the latter reflected heat, and the snow continued unaltered. Q. What is the difference between the radiation and the reflection of caloric ? A. The caloric radiated, is that which properly belongs to the body: the caloric reflected, is that which falls on the surface from other bodies. Q. The tin surface radiated the least heat; but if I touch water, it is insufferably hot, while the wooden black handle, and the black earthenware tea-pot, are comparatively cold. How am I to account for this? 4. On the readiness with which some bodies conduct caloric, when compared with others. Ladies, as to their use, well know the value of highly-polished metallic teapots, from their power to retain heat, and give the entire virtues of the tea. Q. How am I to be assured that some bodies conduct heat more rapidly than others? A. Take three rods of equal size and length; the first of metal, the second of glass, the third of wood: coat one of the ends of each with either melted wax or tallow; then place the other ends in boiling water, or some hot medium; it will be found that the wax will first melt on the metallic rod, next on the glass, and then on the wood, as these are successively conductors of heat. Q. Is there any rule by which good conductors of heat may be known? A. Generally there is. The more dense bodies are, the more rapidly they conduct heat: the more light, with the less facility this is parted with. Metals (platina excepted) are the best conductors of heat; next stones, those that are siliceous the best. Burnt bricks do not conduct heat as well as stones; on which account they are employed in furnaces to prevent the escape of heat. Houses built with brick, and especially those which have mud (cob) walls, are for this reason said to be the warmest abodes. Q. How may I know that dense bodies conduct heat more rapidly than those which are light? A. By placing the hand in quicksilver, on iron, marble, wood, the carpet, or in down. Q. And are not the former colder than the latter? A. A thermometer will teach you that these in the same room are all of equal temperature. Q. Why then do the former feel so cold when compared with the latter? A. From their power to conduct heat rapidly from the |