394 On the CONTRACTION 



that the temperature fliould by that have been reduced*. I 

 fuppofe that the caloric did pafs from the lower ftrata upwards, 



but 



* This experiment may perhaps be thought to give countenance to the opinion 

 of the very ingenious Count Rum ford, that fluids cannot conduft heat, and that 

 no interchange of heat can take place between the particles of bodies iu a fluid, 

 ftate, feeing that for two days the fluid at the bottom of the veffel never fell De- 

 low 39°, though the furface was at 32°. 



From the circumftances detailed in his feventh effay, the Count concluded, that 

 heat cannot defcend in a fluid. From the prefent, it might with equal juilice be 

 inferred, that heat cannot afcend. 



Had I not the fullefl conviftlon that this celebrated philofopher has puflied his 

 ideas too far, I might be difpofed to confider this experiment as according well 

 with the hypothefis. 



Soon after the interelling fpeculations of the Count appeared, I began to inve- 

 ftigate the fubjeft ; and, by a pretty long train of experiments, which I have an- 

 nually taken an opportunity of detailing in my leftures, fatisfied myfelf that he 

 affigned to fluidity a charatler that does not belong to it. Though fince the date 

 of thefe experiments, the public has become poflTelTed of feveral feries, well de- 

 vifed, and, in my opinion, of ihemfelves concluCve, it may yet be worth while to 

 ftate the tenor and refultof them, by which the value of their teftimony in favour 

 of the conducing power of liquids may be eftimated. 

 The experiments were of two defcriptions. 



The one fet, of the fame nature nearly with thofe of Count RtJMFORD, was de- 

 figned to examine, Whether heat, when applied to the furface, can defcend in a 

 fluid; and the other to difcover. Whether, on the mixture of difierent portions of 

 fluid at different temperatures, an interchange of caloric takes place between the 

 particles ; — Water, oil and mercury, having been the fubjefts of the Count's expe- 

 riments, were employed for the firft fet. 



To explore the conducing power of water and oil, the apparatus which I ufed 

 confided of two veliels of tinned iron, both cylindrical, and the one fomewhat lar- 

 ger than the other, Tlie larger had a diameter of eleven inches, and into it were 

 poured the fubjefts of the trial, to different depths on different occafions. The 

 fmaller was ten and a half inches in diameter. By tliree hooks it was fufpended 

 within the larger pan, in fuch a manner, that the bottom of it exaftly reached and 

 came in contadt with the furface of the fluid. This fmaller veffel became the 

 fource of the heat, by being filled with boiling hot water. The water was chan- 

 ged frequently, care being taken to avoid, by the ufe of a fyphon, all agitation 

 and difturbance. 



In 



