in Fluids. 343 



As mercury, which is a metal in fusion, is different in 

 many respects from all other Fluids, I was very impa- 

 tient to know if it agreed with them in that essential 

 property, from which they have been denominated non- 

 conductors of Heat, and this I found to be actually the 

 case, by the result of the following decisive experiment. 



Experiment No. 56. 



Having emptied and cleaned out the cylindrical glass 

 jar used in the last-mentioned experiment, and replen- 

 ished it with a fresh cake of ice, with a conical projection 

 in the middle of its upper side, I placed the jar, sur- 

 rounded by pounded ice and water, on the table, in the 

 cold room, where the foregoing experiment had been 

 made ; and poured over the cake of ice as much ice-cold 

 mercury as covered it to the height of about an inch. 

 Having cleaned the surface of the mercury in the jar 

 with blotting-paper, I suffered the whole to remain quiet 

 about an hour; and then very gently introduced the end 

 of the hot cylinder of iron (inclosed in its paper sheath) 

 into the mercury, and fixed it immoveably in such a po- 

 sition, that its flat end, which was naked, was immedi- 

 ately over the point of the conical projection of ice, and 

 distant from it about ^ of an inch ; where I suffered it 

 to remain several minutes. 



It is necessary that I should mention, that, in order 

 to prevent the internal motions in the mass of mercury, 

 which would otherwise have been occasioned by the rising 

 and spreading out on its surface of those particles of that 

 fluid, which, having touched the flat end of the hot iron, 

 became specifically lighter in consequence of their in- 

 crease of temperature, the end of the hollow cylindrical 

 sheath, in which the solid cylinder of iron was placed, 



