Of WATER by HE AT. 397 



Experiment IV. 



I took the fame tall jar, and flopping the tubulature with a 

 cork, I filled it with water of temperature 40 °, and placed it in 

 a pan. After fufpending two thermometers, as in experiment 

 firft and fecond, I poured a mixture of ice and fait into the pan, 

 to the depth of 4.2 inches, the air of the room being 40 °, as in 

 the laft experiment. 



Bottom. Top. Air. 



Eleven o'clock, 40 ° 40 ° 40 



In 10 minutes, 38+ 38-f- 



— 20 38— 38— 



— 3° 37— 37— 



— 40 36 36 



__ 60 35 . s 35 . 5 



— 80 35 35 



— 100 34.5 3S 



-120 34— 34 



— 8 hours, 34— 34 



e 



A crust of ice began to form on the infide of the glafs 

 when the water in the axis of the bottom and of the top was at 

 36 . In the courfe of the experiment, it became at leaft an inch 

 thick. 



We learn from this experiment, that cold applied to the lower 

 part of a cylinder of water, nearly 18 inches long, and having 

 the temperature of 40 % is actually as fpeedily perceived at the 

 fummit as in the axis of that part, on the external furface of 

 which it immediately acts. As fluids conduct heat fo very tar- 

 dily, this can only arife from currents of cooled water afcend- 



ing 



