THEORIES OF HEAT. i^g 



to that of the fluid, f j is the whole heat of the folld to that of 

 the fluid. But it is a widely different thing to determine pre- 

 cifcly the capacities of airs, and various other fubflances, ex- 

 periments on which are fubjed to great inaccuracy, and niuft 

 be carefully repealed many times before a philofopher fliould 

 pretend to draw final, and ftill lefs elementary, conclufions. 

 Many of the experiments by which contradictory rcfults have 

 been obtained were made, (as I am told, for I have not yet 

 had an opportunity of examining myfelf) by the calorimeter, 

 an inftrument liable to great and deferved objeflions. Lavoifler, 

 by mixing fulphuric acid and water made the natural zero 

 5803 : my father by a fimilar procefs fomewhere I think be- 

 tween 8 and 900. What will Dr. Thompfon make of this? 

 Surely he will not conclude the theorem falfe, but one expe- 

 menter wrong ; moft likely both inaccurate. 



It is very ftrange indeed that Dr. Thompfon fliould have Dr. Tho;npf:in 

 found it difficult to underftand how thefe 140° enter ice during .h/Y'^=''"°"^'! ?* 



r r -I -r ■ *ii i r " if the capacities 



tulion without railing its temperature. AW he lays amounts of ice were not 

 to this, that a given quantity of l)eat will have more efTecl in <^hanged dunng 

 .- , r ■ I 1 r T. 1 • the experiment- 



raiung the temperature or ice than that or water. But the ice 



mufl: continue ice, and the water wafer, and a change of ca- 

 pacity alters the whole reaforiing. Before he can tell whether 

 140 fliould be 14 or not, he muft tell me the whole heat of ice, 

 and let me examine whether that be to itfelf plus, 140as 9 : 10 



or not. He is exactly in the fame error witii regard to fleam. _ , . 



, ,. ,-' 1- 1 • • ,• ■ I r^^' Irvine's 



As to a mode of nndmg the capacities or ice and water, of method of afcer- 

 ' which my father was the undoubted difcoverer, as well as of t^^'n'ngthecapa- 

 the general fad that all bodies change their capacity and form wa't"r"warby" 

 together, one of Irvine's modes was this: he mixed fine river afcertaining how 

 fand waflied, or fine pounded glafs of a given temperature '"^"^l]^^^^^^*"'^ 

 with each, fo as to raife or reduce each an equal number of equal change of 

 degrees. Then the capacities were as the quantities of glafs temperature m 

 added to produce the fame efTe6t. 



Dr. Thmnpfon fays, that there is no proof that the capaci- f^;^ J'j^JPj'jJ 

 ties of bodies are as their abfolute heats. The capacity of iron, capacities are not 



he continues, is greater than that of water or even that of azotic ^!°''^^^? ^^ ^® 



. .° . . the abfolute 



gas, yet it is improbable that iron contains more heat than heats. 



thefe fubftances. Now where did Dr. Thompfon find that I",fta"« of «ron» 



.the capacity of iron was greater than that of water and azotic greater capaciW 



gas? not in his own table furely. Tbere iron by weight has and contain lefs 



capacit_y 0.1264, water 1.000, azotic gas, 0.7036, or as Dr. J;"/J^!2b«t 



Crawford miftakcnly. 



