E.vpenmeiitt refpeBliig the Tratifition of Heat through Fluids. 29 ■^ 



»p;-eareil ftatlonarj', when it was taken out, and immediately plunged in melting ice, and 

 the times of its defcent carefully noted. 



As foon as this apparatus was completed, tlic Count was defirous of afcertaining whether 

 apples wliich continue hot fo long in pies nrade of that fruit, do really polTefs a power of 

 retaining heat greater than that of pure water, of wlilch for the mofl part they confiil; but 

 in the hrft place he afcertained the quantity of fibrous matter in apples, by ftewing two 

 ounces troy of the pulp, and wafliing oil" the foluble matter with a large quantity of cold 

 water. The fibrous remainder, when thoroughly dried, weighed only 25 grahis, wliich, by 

 remaining for feveral days in a plate on the top of a heate"!;! German ftovc, was further re- 

 duced to iS/sths, or Icfs than i-5oth part of the whole mafs. 



Therefults obtained by furrounding the bulb of the pafliige thermometer with a quantity 

 of ftewed apples, fo confiftent as not to exhibit figns of fluulity, and then expofing the ap- 

 paratus to the heating and cooling procefles, are tabulated in the original EfTay. The con- 

 duifting power of the ftewed apples proved to be little more than half that of pure water; 

 that is to fay, the heat was nearly twice as long in palBng through the former as tlie 

 latter. 



As the attention of our author was fteadily fixed on the pofition that heat is communi- 

 cated by fluids, only by its being tranfported by virtue of their intefline motion produced by 

 the change of fpecific gravity, he concluded that there may be two ways of obltrucling this 

 propagation of heat ; namely, by diminifliing their fluidity, which may be done by folution 

 of any mucilaginous fubftance; or, more fimply, by impeding the motion of their particles, 

 which may be efFe£led by mixing any folid fubltance with them which is an imperfect 

 eonduftor of heat, and of an enlarged furface by being divided into fmall mafles. 



In the experiments with ftewed apples, the paflage of the heat in the water, which con- 

 ftituted by far the grcatell part of the mafs, was doubtlefs obllrufted in both theie ways. 

 The mucilaginous part of the apples diminiflied very much the fluidity of the water, at the 

 fame time that the fibrous parts ferved to embarrafs its motions. 



In order to difcover the comparative effeifls of thefe two caufes, water was boiled witii 

 about i-i2th part of its weight of ftarch, and examined by the apparatus. The fame weight 

 of cider-down was alfo boiled with a like quantity of water. The intentiort of this lalt 

 boiling was to free the eider-down from water. From the tabulated experiments, it appears 

 that thefe feveral additions impaired the conduifting power of water nearly to a degree of 

 equality with the ftewed apples. 



In the Philofnphical Tranfaftions for 1792, where Count Rumford has afcertained that 

 heat is adlually propagated in air in the fame manner as it is here ftated to be propagated in 

 water, he found that the thicknefs of a ftratum of air, which ferved as a barrier to heat, re- 

 maining the fame, the pafliige of heat through it was fometimes rendered more difficult by 

 increafing the quantity of the light fubftance, which was mixed with it to cbftruil: its in- 

 ternal motion. To fee if fimilar ellcfts would be produced with water, he repeated the 

 experiments with eider-down, reducing the quantity of it mixed with water to one fourth 

 of the quantity ufcd in tlie former experiments. The rcfiftance to the pafiage of heat was 

 confUlcrably diminilhcd. 



'I he rcfults of thefe experiments are extremely intcrefting; they not only make us ac- 

 quainted with a new and vc-y curious facHr, namely, that feathers, and other like fubftanccs, 



whicii 



