ill Fluids. 275 



of being permitted to swim on water, it were confined at 

 the bottom of it or at any given distance below its sur- 

 face, could in any way affect the temperature of the su- 

 perincumbent water, or prevent its receiving Heat from 

 other bodies. 



Were water a conductor of Heat, there is no doubt 

 but that the influence of the presence of the ice would 

 be propagated in the water in all directions. 

 • The metals are all conductors of Heat, and Professor 

 Pictet found, by an ingenious and decisive experiment,* 

 that in a bar of copper ^i^ inches in length, placed in a 

 vertical position. Heat passed downwards as well as up- 

 wards, and nearly with the same facility in both these 

 directions ; and if it can be shown that Heat cannot de- 

 scend in water, that alone will, I imagine, be thought 

 quite sufficient to prove that water is not a conductor of 

 Heat. 



When we meditate profoundly on the nature of Flu- 

 idity, it seems to me that we can perceive some faint 

 lights which might lead us to suspect that the cause, and 

 I may say the very essence, of fluidity, is that property 

 which the particles of bodies acquire when they become 

 fluid, by which all farther interchange or communication 

 of Heat among them is prevented. But however this 

 may be, the result of the following experiments will cer- 

 tainly be considered as affording indisputable evidence 

 of one important fact respecting the manner in which 

 Heat is propagated in water. 



Experiment No. 15. 



Into a cylindrical glass jar 4.7 inches in diameter and 

 14 inches high, I fitted a circular cake of ice nearly as 



* Essais de Physique, Tome I. Geneve. 1790. 



