32 MEMOIR OF DR. DALTON, ANI) 



1799, he read a paper entitled " Experiments and observations 

 on the power of fluids to conduct heat, with reference to Count 

 Rumford's seventh essay on the same subject."* 



He seems evidently to have made up his mind at once that 

 Count Rumford had drawn a wrong conclusion from his 

 premises, and we see in the reasoning much minute ingenuity 

 and acuteness. As an example of his mode of experimenting 

 and reasoning, the following may be given, p. 381. 



" Exp. 3. Took an ale glass of a conical figure, 2J inches 

 in diameter, and 3 inches deep ; filled it with water that had 

 been standing in the room, and consequently of the temperature 

 of the air nearly. Put the bulb of a thermometer to the 

 bottom of the glass, the scale being out of the water ; then 

 having marked the temperature, I put the red-hot tip of a 

 poker half-an-inch deep into the water, holding it there steadily 

 about half-a-minute ; and as soon as it was withdrawn, I dipped 

 the bulb of a sensible thermometer about ^ inch, when it rose 

 in a few seconds to 180.° 



Temperature. 



Time. At Top. Middle. Bottom. 



Before the poker was immersed ... ... 47^ 



— ... 180° ... — ... 47° 



5min. ... 100° ... 60° ... 47^° 



20 „ ... 70° ... 60° ... 4r 



1 hour ... 55° ... — ... 52°" 



After other experiments he says, p. 385, "We must con- 

 clude, therefore, that the quick circulation of heat in water 

 over a fire, &c., is owing principally to the internal motion 

 excited by an alteration of specific gravity; but not solely 

 to that cause, as Count Rumford has inferred." 



Avery simple and ingenious experiment is related on the same 

 page. He mixed hot and cold water, stirred for half-a-minute, 

 and tried if the upper part became hotter than the lower, it 



* Same vol., p. M73. 



