256 Of the Propagation of Heat 



of certain substances, on being mixed with water, tend "very 

 powerfully to impair the conducting power of that Fluid in 

 regard to Heat. 



In the experiments No. i and No. 2, which were both 

 made on the same day, and in the order in which they 

 are numbered, the Heat was considerably more obstructed 

 in its passage through the mass of stewed apples which 

 surrounded the thermometer than in the experiments No. 

 3 and No. 4, which were made on the following day. It 

 is probable that this was occasioned by some change in 

 the consistency of this soft mass of the stewed apples 

 which had taken place while the instrument was left to 

 repose in the interval between the experiments ; but in- 

 stead of stopping to show how this might be explained, 

 I shall proceed to give an account of some experiments 

 from the results of which we shall derive information 

 that will be much more satisfactory than any speculations 

 I could offer on that subject. 



Supposing Heat to be propagated in water in the same 

 manner as it is propagated in air and other elastic Fluids, 

 namely, that it is transported by its particles, these parti- 

 cles being put in motion by the change which is pro- 

 duced in their specific gravity by the change of temper- 

 ature, and that there is no communication whatever, or 

 interchange of their Heat, among the particles of the same 

 .Fluid; in that case it is evident that the propagation of 

 Heat in a Fluid may be obstructed in two ways, namely, 

 by diminishing its Fluidity (which may be done by dis- 

 solving in it any mucilaginous substance); or, more simply, 

 by merely embarrassing and obstructing the motion of 

 its particles in the operation of transporting the Heat, 

 which may be effected by mixing with the Fluid any solid 

 substance (it must be a non-conductor of Heat, how- 



