ON FLUIDS AS CONDUCTORS OF HEAT". l5^ 



and ralfed a thermometer placed at the bottom of the liqufd : 

 to avoid communication by the fides of the vefTel, a bad con- 

 du<5ting fubflance was made choice of, and he afcertained, 

 hy means of a thermometer placed in the fame liquid near 

 the fide of the velFel, that no current was cftabliflied which 

 differed in the temperature : finally, the motion of the bubbles 

 which were difengaged, and the other appearances of the 

 liquid, convinced him that currents were not formed. 



In thefe experiments* it was proved, that liquids were — and that oil 

 (fifFerent in their conducing faculty; the penetration of the ^^j.^g^jf^gj^'""'^ 

 heat from the top to the bottom, was five times flower in oilniercury. 

 than in mercury. 



Rumford fuppofed that the flightefi: changes of fpecific 



gravity were accompanied by a locomotion, which produced 



a current, and he endeavoured to render it vifible, by ex- 



pofing an alkaline liquor, in which were fufpended very fmall 



fragments of amber, which he found had the fame fpecific 



gravity as the liquid, to a change of temperature : but Thorn- Thomfon found 



fon has Qiown +, that the motions obferved in thefe moleculiE ^^f^^h^ motions 



- . „ of 'olids do 



were illufory, and that, in thefe variations of temperature, not prove any 



which are gradual, they appear to be owing mily to the dif- '^"'i''^"'^'' '" ^^« 



ference of fpecific gravity which they acquire, and to the ad- * 



herence of air-bubbles, fo that fome ot thele moleculae move 



in contrary diredions, and run againfi: each other without 



following the direflicMi of the currents, he has alfo (liown that 



thefe floating corpulcules might receive different motions while 



the flrala of the liquid maintained a perfect tranquillity: he 



put water, tinged blue by juice of red cabbage into a glafs vef- the floating 



fel; he afterwards poured clear water on it with great precau- ^°^'^'^^ ^°^^ ^^^ 



lion, by means of a tube with a capillary extremity; thus he n^uiefcent fiTulds 



kept the two liquids feparate and dJltiii6l; he then heated the ^f difierent 



veffel gently at the bottom : it is manifeft that if a current had °""^** 



been C'ftabliflied, it would have been marked by the coloured 



liquid, but the feparation of the two liquids was preferved un- 



confufed ; moreover the corpufcules put into the firfi: liquid 



moved upwards and downwards, and croffed the line of fepa- 



* Bibl. Brit. Tom. XVIII. or Philofophic Journal, Quarto fories. 

 V. 197. 



f Nicholfon's Journal, 06tavo, for Feb. 1802. See alfo a me- 

 moir by this philofopher, in the Journal for March, 180J, contain- 

 ing the earliell experimental examination of the Count's doctrine. 



ration 



