HEAT. 



ches above the surface of ice,surrounding 

 the under part of the jar with pounded 

 ice, and water. A solid cylinder of iron, 

 l inch in diameter, and 12 inches long, 

 to which a sheath of thick paper to pre- 

 serve its heat was adapted, being heated 

 to 210 by immersion in water, it was 

 introduced into the sheath, and sus- 

 pended in the jar in such a manner, that 

 the middle of its lower extremity was 

 directly above the pointed projection of 

 ice, and distant from it only t^ths of an 

 inch. If any heat had descended through 

 the thin stratum of oil, interposed be- 

 tween the hot iron and the projection of 

 ice under it, it must have been apparent, 

 by the melting of the ice. But this was 

 not the case ; the ice did not appear to 

 be diminished, or otherwise affected by 

 the hot iron. When mercury was sub- 

 stituted instead of oil, the hot iron 

 was placed at the distance of $-inch 

 from the ice without affecting it. 



Dr. Murray remarks, that all the ar- 

 rangements in this experiment are such 

 as to occasion waste of heat, and to 

 prevent the conducting power of the 

 fluid, if it had any, from being apparent. 

 Instead of using a little oil only, the ice 

 was covered to the height of three in- 

 ches, and this oil was kept as nearly as 

 possible at 32 during the whole of the 

 experiment. The heated cylinder being 

 suspended in the oil, the portions of oil 

 nearest to its surfaces would be heated, 

 and expanded, and would therefore as- 

 cend ; other portions would successively 

 come in contact with the iron, and simi- 

 lar effects would be produced upon 

 them ; and this circulation would con- 

 tinue as long as the iron continued to 

 impart caloric to the oil ; the ascending 

 current being in the middle of the jar, 

 and the descending current keeping near 

 to the sides. By this circulation it is 

 obvious that no caloric could be com- 

 municated to the ice, until the whole of 

 the liquid arrived at a higher tempera- 

 ture than 32. The rise of temperature 

 of the liquid in the jar must have been 

 greatly retarded by its being surrounded 

 with ice and water. In addition to this 

 it has been remarked, that this mode of 

 detecting the communication of caloric, 

 by the melting of ice, is unfavourable ; 

 since in that operation, a large quan- 

 tity of caloric is absorbed, and a por- 

 tion might be actually communicated 

 to the ice, and yet might not be able to 

 melt a sufficient quantity to render its 

 effects apparent. 



The results of experiments by many 



different philosophers, are hostile to the 

 assertion of Count Rumford, that fluids 

 are absolutely non-conductors of caloric. 



Dr. Hope applied heat to the surface 

 of water in a vessel eleven inches in 

 diameter, and at the same time con- 

 trived that a stream of water should cir- 

 culate on the outside, to prevent the con- 

 ducting power of the sides of the vessel 

 from affecting the result ; heat was con- 

 ducted downwards, as appeared by the 

 indications of a thermometer placed at 

 some depth below the surface of the 

 fluid. Dr. Hope also mixed portions of 

 hot and cold water, and, after agitating 

 them, permitted them to remain at rest 

 for a time : no separation took place of 

 the hot from the colder portions, but the 

 whole had attained one uniform tem- 

 perature, which is considered to be in- 

 consistent with the theory of Rumford. 

 Similar facts were ascertained by 

 Thomson, Nicholson, and Dalton ; but 

 the most satisfactory and conclusive 

 experiment was made by Dr. Murray 

 of Edinburgh, the original account of 

 which was published in Nicholson's 

 Journal, Svo. Vol. I. page 241. It ap- 

 peared to him that all the precautions 

 which had previously been taken to 

 obviate errors, arising from the con- 

 ducting powers of the vessels in which 

 the experiments were performed, were 

 insufficient for that purpose ; and a 

 more effectual method was invented by 

 him. Since ice cannot have its tem- 

 perature raised above 32, it occurred to 

 him that a vessel of that substance 

 would answer well for holding fluids, 

 the conducting power of which is in- 

 tended to be tried ; for whatever degree of 

 heat may be applied to it above, it can- 

 not conduct the heat downwards, the 

 melting of a part of the ice being the 

 only effect which it would be capable 

 of producing. Heat being applied to 

 the surface of a fluid, under such cir- 

 cumstances, if that fluid, should have its 

 temperature increased below, it may be 

 with certainty inferred that such increase 

 is owing to the conducting power of the 

 fluid itself, and not to that of the vessel 

 in which it is contained. 



Mr. Murray gives the following ac- 

 count of this experiment in his System 

 of Chemistry, third edition, Vol. I. page 

 305. "In a hollow cylinder of ice, a 

 thermometer was placed horizontally, 

 at the depth of one inch, its bulb 

 being in the axis of the cylinder, and 

 the part of the stem to which the scale 

 was attached, entirely without. As 



