242 Of the Propagcdion of Heat 



is to say, that, although the particles of any Fluid, indi- 

 vidually^ can receive Heat from other bodies or commu- 

 nicate it to them, yet among these particles themselves 

 all interchange and communication of Heat is absolutely 

 impossible. 



It may, perhaps, be thought not altogether uninterest- 

 ing to be acquainted with the various steps by which I 

 was led to an experimental investigation of this curious 

 subject of enquiry. 



When dining, I had often observed that some particu- 

 lar dishes retained their Heat much longer than others, 

 and that apple-pies, and apples and almonds mixed 

 (a dish in great repute in England), remained hot a sur- 

 prising length of time. 



Much struck with this extraordinary quality of retain- 

 ing Heat which apples appeared to possess, it frequently 

 occurred to my recollection ; and I never burnt my 

 mouth with them, or saw others meet with the same mis- 

 fortune, without endeavouring, but in vain, to find out 

 some way of accounting in a satisfactory manner for this 

 surprising phaenomenon. 



About four years ago, a similar accident awakened my 

 attention, and excited my curiosity still more : being en- 

 gaged in an experiment which I could not leave, in a 

 room heated by an iron stove, my dinner, which con- 

 sisted of a bowl of thick rice-soup, was brought into the 

 room, and as I happened to be too much engaged at the 

 time to eat it, in order that it might not grow cold, I 

 ordered it to be set down on the top of the stove ; about 

 an hour afterwards, as near as I can remember, beginning 

 to grow hungry, and seeing my dinner standing on the 

 stove, I went up to it and took a spoonful of the soup, 

 which I found almost cold and quite thick. Going, by 



