1821.] Mr. Herapath's Reply to Mr. Tredgold. 305 



In a letter from Sir H. Davy, dated Jan. 13, 1821, he says : 

 " I have read th* parts of your paper, which are intelligible 

 without profound mathematical study, with attention ; and highly 

 ingenious as I find your views, 1 must say I am not impressed 

 with a conviction of their truth. 



" The pressure of your gravific fluid, for instance, taking away 

 weight, must depend upon the motion of its particles ; and yet 

 you counteract this pressure by heat which you consider as 

 motion." 



On this passage I beg leave to observe, that a paper such as 

 this, which is strictly mathematical, cannot be judged by general 

 views. The President himself was aware of this ; and in a 

 conversation I had the honour to have with him at one of his 

 Wednesday evening meetings, intimated that he laid no stress 

 at all on his objection. 



In the same letter, SirH. says, 



" There is so much ingenuity, and so minute an acquaintance 

 with the progress of discovery, displayed in your paper, that I 

 cannot help wishing that its views and objects had been directed 

 to a matter of pure experimental inquiry. For instance, the 

 doctrine of heat and the investigation of its laws, supposing it 

 to be motioiii Such a preliminary paper, if satisfactory, would 

 prepare the philosophical world for greater and more abst-use 

 researches." 



In a note of Jan. 30, Mr. Gilbert, speaking of the reason of 

 his having first objected to present the paper to the Royal 

 Society, says, 



" On your account, as well as on my own, I did not like to 

 present a paper of so much importance, and embracing so very 

 wide afield, without consulting two or three members," &c. 



The only other passage I shall quote is from a note of Sir H. 

 Davy, dated March 6. 



' Having considered a good deal the subject of the supposed 

 real zero," says Sir H. Davy, " I have never been satisfied with 

 any conclusions respecting it. 1 cannot see any necessary con- 

 nexion between the capacity of bodies for heat and the absolute 

 quantity they contain ; and temperature does not measure 

 a quantity, but merely a property of heat." 



In my reply to this part, dated March 8, I observed : 

 " You are aware that I conceive heat to consist in motion ; 

 and that the temperature of a body is the intensity of the intes- 

 tine motion of its particles estimated, when you compare the 

 temperatures of different bodies, not by their velocity, but their 

 momentum. The degree, therefore, of absolute cold is where 

 the particles have no motion ; and my object has been to ascer- 

 tain this by determining the ratio of the intestine motions at two 

 fixed points, as those of ice melting, and water boiling. What 

 is called the " capacity of bodies for caloric," I have demon- 

 New Series, vol. n. x 



