observed on the Glaciers of Chamouny. 253 



results of which no person to my knowledge has yet 

 explained. 



There is another very curious natural phenomenon 

 which I could wish to see explained in a satisfactory man- 

 ner by those who still refuse their assent to the opinions 

 I have been led to adopt, respecting the manner in which 

 heat is propagated in fluids. The water at the bottoms 

 of all deep lakes is constantly at the same temperature 

 (that of 41 Fahrenheit), summer and winter, with- 

 out any sensible variation. This fact alone appears to 

 me to be quite sufficient to prove that, if there be any 

 immediate communication of heat between neighbouring 

 particles or molecules of water, de proche en proche ^ or 

 from one of them to the other, that communication must 

 be so extremely slow that we may with safety consider 

 it as having no existence ; and it is with this limitation 

 that I beg to be understood when I speak of fluids as 

 being non-conductors of heat. 



In treating of the propagation of heat in fluids, I 

 have hitherto confined myself to the investigation of 

 the simple matter of fact, without venturing to offer 

 any conjectures relative to the causes of the phenomena 

 observed. But the results of recent experiments on the 

 calorific and frigorific radiations of hot and of cold bodies 

 (an account of which I shall have the honour of laying 

 before the Royal Society in a short time) have given 

 me some new light respecting the nature of heat and the 

 mode of its communication; and I have hopes of being 

 able to show why all changes of temperature in trans- 

 parent liquids must necessarily take place at their sur- 

 faces. 



I have seen, with real pleasure, that several ingenious 

 gentlemen in London and in Edinburgh have under- 



