*5 
observed on the Glaciers of Cbamouny, &c. 
There is another very curious natural phenomenon, which I 
could wish to see explained in a satisfactory manner, 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 0 Fahrenheit,) summer and winter, 
without any sensible variation. This fact alone appears to me to 
be quite sufficient to prove, that if there be any immediate com- 
munication 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 commu- 
nication ; and I have hopes of being able to show why all changes 
of temperature, in transparent liquids, must necessarily take 
place at their surfaces. 
I have seen with real pleasure, that several ingenious gen- 
tlemen, in London, and in Edinburgh, have undertaken the 
investigation of the phenomena of the propagation of heat in 
fluids; and that they have made a number of new and inge- 
nious experiments, with a view to the farther elucidation of that 
E 
MDCCCIV. 
