' On the. ConduBing Potoif of Fluids v/lth Regard tt Heat. 197 



X. 



Experiments on the ConduEling Power of Fluids nvith Regard to Heat.—'W. N. 



A, 



^MONG the papers prefented to the philofophical world fmcethc commencement of 

 the prefent Journal, none occupy a higher rank than the experiments and dedudlions of 

 Count Rumford on heat ; whether we attend to their extenfive and important confequences, 

 or the powers of philofophical inveftigation they exhibit. One of the moft Cngular fa£ls 

 he has noticed is the flownefs with which heat is condufled through fluids } a fa£l long ago 

 pointed out and ftrikingly imprefled by him, and latterly rendered more remarkable by his 

 inference, that bodies in the Hate of fluidity have abfolutely no power of conducing heat 

 from particle to particle, but convey. It from one folid to another merely by their motions 

 or currents. Whether this inference taken in the extreme of ftri£tnefs could be juftified 

 by his own, or indeed by any experiment, was doubted by myfelf as well as others } but 

 without treating the fubjeft in that precife manner, it becomes a queftion of fome intereft 

 and curiofity, to decide whether the direft condu£ling power of fluids be too minute to be- 

 afcertained by careful experiments more or lefs varied from thofe of the Count. Do£lor 

 Thomfon, of Edinburgh, is, I believe, the firft who undertook and conduced a procefs of 

 this kind, an account of which is given in his able paper in our laft volume, p. 529. I 

 need not here advert to the particulars of that memoir, farther than to remark, that in the 

 difcudion of this fubje£t in converfation by fome philofophical friends who meet weekly at 

 my houfe, our confideration was more particularly diredled to the argument which is drawn 

 at p.- 534, in favour of the condenfing power of fluids from the Count's own experiments. 

 It is there obfeived. that when ice was flowly melted by boiling hot water {landing over it, 

 with the interpoGtion of a thin ftratum of ice-cold water, there were undoubtedly currents, 

 produced through this laft flratum, becaufe water becomes denfer either by receiving or 

 lofing heat till it arrives at 40" ; but it is contended, that the heat which pafl'ed to the cold 

 water in this procefs muft have been condufted from particle to particle, and not conveyed 

 by currents of the fuperior water ; and farther, that the regular diminution of the numbers- 

 expreffrng the temperatures of the ftrata of water from the furface downwards, is incon- 

 fiftent with the fuppofuion of fuch currents, which it Ihould feem ought to produce a 

 mixture of the fluid. 



It appeared to us, that the principal queftion in this cafe was, whether or not the whole 

 conveyance of the heat were efFefted by the mediation of the vefliel or folid ; which it ought 

 to be if the folid be the only proper and perfefl conduftor prefent ? That is to fay, if heat 

 be applied to the furface of a fluid, and the efi^eft of that heat be to produce rarefaftion, it 

 muft inevitably follow, in this fimple ftatement of the cafe, that no heat would pafs below 

 the range of particles at the very furface where the heat was applied, unlefs the fluid itfelf 

 ■were properly and ftridtly a cbnduftor. 



But 



