S4» DALTON ON THE ZERO O* HEAT! 



into the ground. If wood is rotten, the fcrew cannot act. I a(Tur£ 

 you, that when I go abroad, I conftantly fee great quantities of 

 roots in a rotten ftate, about almoft every farm-houfe, which 

 would not be the cafe if the utility of the inftrument were made 

 public. I am, 



Your much-obliged friend, and humble fervant, 

 Wijvfair, March 26, 1802. J.LLOYD. 



VII. 



Letter from Mr. Dal ton, containing Observations Concerning 

 the Determination of the Zero of Heat, the thermometrical 

 Gradation, and the Law by which denfe or non-elajlic Fluids 

 expand jby Heat. 



Manchefter, April 20th, 1803. 



To Mr. NICHOLSON. 

 SIR, 



Remarks on a IN your laft Number, page 221, a correfpondent has ad- 



letter in our lad verted to an hypothefis which I fuggefted in my account of 



eernine'the real experiments on the expanfion of elaflic fluids. It was, that 



zero of heat. " the repulfive force of each particle [of gas] is exactly pro- 



** portional to the whole quantity of heat combined with it, 



when fubject to a given preilure. Having previoufly found 



that 1000 parts of any elafb'c fluid, at temperature 55°, were 



expanded to 1325 at 212°, it followed from the hypothefis, 



that the quantity of heat in air, of 55°, is to the quantity in 



air of 212 & , as -y/1000 : ^1325, or as 10 : 10.9834- : from 

 which the real zero is deduced at 1573° below the freezing 

 point of water. I had moreover noted, that for 78-|° (as the 

 abovementioned writer has juftly corrected it) the expanfior* 

 of air was 16*7 parts, and for the other 7$j°, only 158. — • 

 From thefe data, calculating, as he fays, upon my hypothefis, 

 lie has deduced two other points for the real zero ; namely, 

 $714°, and 1486° : thefe inconfiftent refults, he thinks, tend 

 to difcredit, either the hypothefis, or the accuracy of the ex-* 

 periments. Now he mull give me leave to obferve, that the 

 two lafl deductions are not derived from my hypothefis, but 

 from another totally inconfiftent with it ; namely that the? 

 mercurial thermometer is an accurate meafure of heat. For,, 

 upon the hypothefis that the real temperature is as the cube- 

 root 



