Finding that water was so bad a conductor of heat, I was desirous to learn how ice would conduct it, and tried it as follows. Experiment IX. Feb. 9th. Out of a mass of ice, by means of a hot iron, I shaped a cylindrical piece, 3 inches in diameter, and 5 inches long, clean and pure; its weight 17 ounces. Made a small round hole at one end, one inch deep, and the size of a thermometer bulb, which was inclosed in it. The other end of the piece was put into a bason of snow and salt, to the depth of from to 11⁄2 inches, the temperature of which was kept below 10° for 1 hours. Air 37°. Therm. in the liquid. Therm. in the ice. 5° 14 h. at a medium. 7 32° 31/1 N. B. This descent of half a degree was gradual, but did not commence till long after the beginning of the experiment. After this the piece of ice was inclined to one side, by which nearly one half of it was immersed in the cooling liquid, and the inclosed bulb of the thermometer was now not more than an inch from the cold mixture. h. m. Therm. in the liquid. Therm. in the ice. The ice now weighed 124 ounces: the rest had been liquified by the operation of the saline liquor. This experiment, I think, decidedly proves that ice is a worse conductor of heat than water. Indeed this is not wonderful; for it is said, that ice at a low temperature becomes an electric. It is certainly a remarkable circumstance, but not at all inconsistent with the known laws of heat, that in a mixture of hot and cold liquids the uniform temperature should be so soon induced by agitation and so slowly by rest but when we consider, that in the former case hot and cold particles are brought together, and that in the latter there is a series of particles one upon another, gradually rising in temperature, but differing by insensible degrees, we shall not wonder at the facts. When any one particle of water, or any other body, has one above it, warmer by an insensible degree, and another below it, colder by an insensible degree, its power to transmit heat must be very small. These considerations gave rise to the two following experiments. Experiment X. A mercurial thermometer was taken, its bulb inch in diameter, and hanging clear of the scale. It was heated by the flame of a candle to 600°, and then laid upon a table with the bulb projecting over the edge, and was thus left to cool by the mere operation of the air in the room, which was 52°. The following is which, however, the medium result of two experiments, agreed with each other almost in every obscrvation. Experiment XI. Another thermometer, having a similar bulb, but a scale with much larger degrees, was heated and cooled in the same manner. In these experiments we may consider mercury and air mixed together of unequal temperatures, with a thin partition of glass and from the last we may conclude, that the thermometer imparted to the air 40 times more heat in half a minute, when its temperature was 30° above the air, than when it was only 1° above it. We shall now advért a little to Count Rumford's expe riments.—It will easily appear, that arguing fairly upon his own hypothesis he can never account for the pheno-. mena observed: for, hot water being poured upon ice, an internal motion would take place near the surface of the ice, by which a stratum of water of a certain thickness would be reduced to 32°, and then all further reduction of the ice must cease; because all the superincumbent water, being above 53°, would be lighter, and could not descend to the ice. But this is quite contrary to what took place. The facts, however, will admit of a satisfactory explanation upon established principles. By experiments X. and XI. it appears, that the quantity of heat given out by a body, during any small given portion of time, is nearly as the excess of the temperature of the body above the cooling medium. Hence, then, we may conclude, that the effect of hot water upon ice, arising from the proper conducting power of water, will be nearly as, the heat of the water. What effect the other cause may produce, it will be difficult to determine from theory experience will be the best guide. One thing, however, appears pretty certain, that its effect must be a maximum, when the temperature of the water at large is 42°; because then there can never want a determination of the particles downward, to supply the place of the lighter water of 32° degrees ascending. If the temperature of the water exceed 42°, then the effect of the internal internal notion will be less, diminishing by some unknown ratio. As far as I can judge from Count, Rum-* ford's experiments, the joint effects of these two causes should be nearly the same with water of 42o and water of · • 190°. Taking this, therefore, for granted, we shall be enabled to sketch a table of the values of those two causes for every 10° of temperature. The numbers expressing the effect of the proper conducting power, are de rived from the tenth experiment, and consequently are not purely hypothetical: those expressing the other effect, except 42° and 1920, are put down hypothetically, because the law of decrease has not been ascertained. . It is to be supposed, that a given quantity of water, of the several temperatures mentioned, is carefully poured upon a cake of ice, at the bottom of a cylindrical glass jar, and stands without agitation for a given time, as half an hour; then the proportionate quantity of ice supposed to be melted by the two causes separately are stated in numbers, and then the sums are taken to express the joint effects. Temperature |